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Qos For Ipmpls Networks Gallo Mark Zhang Raymond Alvarez Santiago

Qos For Ipmpls Networks Gallo Mark Zhang Raymond Alvarez Santiago Qos For Ipmpls Networks Gallo Mark Zhang Raymond Alvarez Santiago Qos For Ipmpls Networks Gallo Mark Zhang Raymond Alvarez Santiago

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800 East 96th Street Indianapolis, IN 46240 USA Cisco Press QoS for IP/MPLS Networks Santiago Alvarez
ii QoS for IP/MPLS Networks Santiago Alvarez Copyright© 2006 Cisco Systems, Inc. Published by: Cisco Press 800 East 96th Street Indianapolis, IN 46240 USA All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without writ- ten permission from the publisher, except for the inclusion of brief quotations in a review. Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 First Printing June 2006 Library of Congress Cataloging-in-Publication Number: 2004117089 ISBN: 1-58705-233-4 Trademark Acknowledgments All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capital- ized. Cisco Press or Cisco Systems, Inc. cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark. Warning and Disclaimer This book is designed to provide information about quality of service in IP/MPLS networks using Cisco IOS and Cisco IOS XR. Every effort has been made to make this book as complete and as accurate as possible, but no war- ranty or fitness is implied. The information is provided on an “as is” basis. The authors, Cisco Press, and Cisco Systems, Inc. shall have neither liability nor responsibility to any person or entity with respect to any loss or damages arising from the information contained in this book or from the use of the discs or programs that may accompany it. The opinions expressed in this book belong to the author and are not necessarily those of Cisco Systems, Inc. Corporate and Government Sales Cisco Press offers excellent discounts on this book when ordered in quantity for bulk purchases or special sales. For more information please contact: U.S. Corporate and Government Sales 1-800-382-3419 corpsales@pearsontechgroup.com For sales outside the U.S. please contact: International Sales international@pearsoned.com Feedback Information At Cisco Press, our goal is to create in-depth technical books of the highest quality and value. Each book is crafted with care and precision, undergoing rigorous development that involves the unique expertise of members from the professional technical community.
iii Readers’ feedback is a natural continuation of this process. If you have any comments regarding how we could improve the quality of this book, or otherwise alter it to better suit your needs, you can contact us through e-mail at feedback@ciscopress.com. Please make sure to include the book title and ISBN in your message. We greatly appreciate your assistance. Publisher Paul Boger Cisco Representative Anthony Wolfenden Cisco Press Program Manager Jeff Brady Production Manager Patrick Kanouse Development Editor Jill Batistick Senior Project Editor San Dee Phillips Copy Editor Keith Cline Technical Editors Mark Gallo, Raymond Zhang Book and Cover Designer Louisa Adair Composition Mark Shirar Indexer Keith Cline
iv About the Author Santiago Alvarez, CCIE No. 3621, is a technical marketing engineering for Cisco Systems working on MPLS and QoS since 2000. He joined Cisco in the blazing days of 1997. Prior to Cisco, Santiago worked in software development for Lucent Technologies. He has been involved with computer net- working since 1991. Santiago is a frequent speaker at Cisco Networkers and a periodic contributor to Cisco Packet Magazine. He holds a bachelor of science degree in computer science from EAFIT Uni- versity, a master of Science degree in computer science from Colorado State University, and a master of science in telecommunications from the University of Colorado at Boulder. Outside work, he enjoys the outdoors, fine food, and exploring the world as an independent traveler. He can be reached at saalvare@cisco.com.
v About the Technical Reviewers Mark Gallo is a systems engineering manager at Cisco Systems within the channels organization. He has led several engineering groups responsible for positioning and delivering Cisco end-to-end systems, as well as designing and implementing enterprise LANs and international IP networks. He has a B.S. degree in electrical engineering from the University of Pittsburgh and holds Cisco CCNP and CCDP certifications. Mark resides in northern Virginia with his wife, Betsy, and son, Paul. Raymond Zhang is a senior network architect for BT Infonet in the areas of Global IP backbone infra- structure, routing architecture design, planning, and its evolutions. Currently, his main areas of interest include large-scale backbone routing, traffic engineering, performance and traffic statistical analysis, and MPLS-related technologies (including interdomain traffic engineering, GMPLS, metro Ethernet, Diffserve, IPv6, and Multicast). Raymond participates in several IETF drafts relating to MPLS, BGP- based MPLS VPN, Inter-AS TE, and, more recently, PCE-based work.
vi Dedications Thanks for withstanding long, long working hours.
vii Acknowledgments I would like to give special thanks to Bob Olsen and Sandeep Bajaj for sharing their technical expertise through so many years. They have patiently tolerated my constant interruptions and have provided use- ful insight on different topics included in the book. Special thanks to the reviewers, Mark Gallo and Raymond Zhang. I appreciate your detailed comments. I am to blame for any remaining inaccuracies or omissions. Big thanks to Bruce Davie, whose responsiveness at key points encouraged me to persist in my goal. I highly regard his unusual ability to abstract complexity and clearly illustrate the essence of intricate technology concepts. Much of his work has directly and indirectly influenced the content of this book. Similarly, I extend my gratitude to François Le Faucheur and Jean Philippe Vasseur. They have had the patience to discuss with me many aspects of these technologies in numerous occasions. Merci! Thanks to Ramesh Uppili for contributing to the presentation of key topics in multiple ways. I also want to thank Rakesh Gandi, Prashanth Yelandur, Ashish Savla, Bobby Kaligotla, Lawrence Wobker, Ashok Ganesan, Jay Thontakudi, and ScottYow for facilitating the discussion of Cisco IOS XR in this book. Special thanks to the Cisco Press team: John Kane, Chris Cleveland, Jill Batistick, San Dee Phillips, and Elizabeth Peterson. I really appreciate your attention to detail and extraordinary patience with me. I wish John the best in his new endeavors. Finally, if you have read this far in search of your name, this paragraph is for you. I have to acknowledge that numerous individuals contributed through insightful discussions. They unhappily or maybe happily remain anonymous. Thanks!
viii This Book Is Safari Enabled The Safari® Enabled icon on the cover of your favorite technology book means the book is available through Safari Bookshelf. When you buy this book, you get free access to the online edition for 45 days. Safari Bookshelf is an electronic reference library that lets you easily search thousands of technical books, find code samples, download chapters, and access technical information whenever and wherever you need it. To gain 45-day Safari Enabled access to this book: • Go to http://www.ciscopress.com/safarienabled • Complete the brief registration form • Enter the coupon code 2ML4-YT1N-YR8J-D5NQ-DAH4 If you have difficulty registering on Safari Bookshelf or accessing the online edition, please e-mail customer-service@safaribooksonline.com.
ix Contents at a Glance Foreword xv Introduction xvii Chapter 1 QoS Technology Overview 3 Chapter 2 MPLS TE Technology Overview 57 Chapter 3 Cisco QoS 79 Chapter 4 Cisco MPLS Traffic Engineering 143 Chapter 5 Backbone Infrastructure 201 Appendix A Command Reference for Cisco MPLS Traffic Engineering and RSVP 265 Index 282
x Contents Foreword xv Introduction xvii Chapter 1 QoS Technology Overview 3 IP QoS Architectures 3 Integrated Services 4 IntServ Terminology 5 Architecture Principles 5 Service Model 6 Use of RSVP in IntServ 8 Differentiated Services 9 DiffServ Terminology 9 Architecture Principles 10 Differentiated Services Code Point 11 Nodes, Domains, and Regions 13 Traffic Classification and Conditioning 13 Per-Hop Behaviors 15 MPLS Support for IntServ 18 MPLS Support for DiffServ 19 E-LSP 20 L-LSP 22 DiffServ Tunneling Models over MPLS 25 Pipe Model 25 Short-Pipe Model 26 Uniform Model 28 Traffic-Management Mechanisms 31 Traffic Classification 31 Traffic Marking 31 Traffic Policing 32 Traffic Shaping 35 Congestion Management 37 Active Queue Management 40 Link Fragmentation and Interleaving 42 Header Compression 44 QoS Signaling 45 Resource Reservation Protocol 45 Design Principles 46 Protocol Messages 47 Protocol Operation 49 Other QoS Signaling Mechanisms 51
xi Summary 52 References 52 Chapter 2 MPLS TE Technology Overview 57 MPLS TE Introduction 57 Basic Operation of MPLS TE 59 Link Information Distribution 59 Path Computation 60 TE LSP Signaling 63 Traffic Selection 64 DiffServ-Aware Traffic Engineering 64 Class-Types and TE-Classes 66 Bandwidth Constraints 68 Maximum Allocation Model 68 Russian Dolls Model 70 Fast Reroute 71 Link Protection 74 Node Protection 74 Summary 76 References 77 Chapter 3 Cisco QoS 79 Cisco QoS Behavioral Model 79 Classification Component 80 Pre-Queuing Component 80 Queuing Component 81 Enqueuing Subcomponent 81 Dequeuing Subcomponent 82 Post-Queuing Component 84 Modular QoS Command-Line Interface 84 Hardware Support for the MQC 87 Traffic-Management Mechanisms 87 Traffic Classification 88 Traffic Marking 94 Traffic Policing 100 Traffic Shaping 108 Congestion Management 115 Active Queue Management 121 Link Fragmentation and Interleaving 127 Header Compression 128 Hierarchical Configurations 129 Hierarchical Classification 129
xii Hierarchical Policies 130 Percentage-Based Rates 132 Parameter Units 133 Processing of Local Traffic 135 Summary 139 References 140 Chapter 4 Cisco MPLS Traffic Engineering 143 Basic Operation of MPLS TE 143 Enabling MPLS TE 144 Enabling MPLS TE on a Node 144 Enabling MPLS TE on an Interface 145 Defining a TE Tunnel Interface 146 Link Information Distribution 148 Using IS-IS for Link Information Distribution 148 Using OSPF for Link Information Distribution 149 Controlling Flooding 150 Configuring Link Attributes 150 Verifying Link Information Distribution 153 Path Computation 156 Configuring the TE LSP Path 156 Configuring the TE LSP Constraints 157 Path Reoptimization 159 Verifying Path Computation 160 Signaling of TE LSPs 163 Configuring RSVP 163 Verifying RSVP 164 Verifying Signaling of TE LSPs 167 Traffic Selection 172 Traffic-Selection Alternatives 172 Class-Based Tunnel Selection 173 DiffServ-Aware Traffic Engineering (DS-TE) 175 Prestandard DS-TE 175 Class-Types and TE-Class 176 Defining a DS-TE Tunnel Interface 177 Configuring Bandwidth Constraints 179 Verifying DS-TE Link Information Distribution 181 Verifying Signaling of DS-TE LSPs 182 Fast Reroute (FRR) 182 Link and Node Protection 183 Bandwidth Protection 187
xiii Verifying FRR on the Headend 191 Verifying FRR on the PLR 193 Summary 198 References 198 Chapter 5 Backbone Infrastructure 201 Backbone Performance 201 Performance Requirements for Different Applications 202 Segmentation of Performance Targets 204 Factors Affecting Performance Targets 206 Latency Versus Link Utilization 207 Reference Network 210 Edge Nodes 210 QoS Design Alternatives 212 Best-Effort Backbone 213 Best-Effort Backbone with MPLS TE 219 DiffServ Backbone 226 DiffServ Backbone with MPLS TE 233 DiffServ Backbone with DiffServ-Aware Traffic Engineering 240 Adding MPLS TE FRR 251 What Design Should I Use? 260 Summary 261 References 261 Appendix A Command Reference for Cisco MPLS Traffic Engineering and RSVP 265 Index 282
xiv Icons Used in This Book Command Syntax Conventions The conventions used to present command syntax in this book are the same conventions used in the IOS Command Reference. The Command Reference describes these conventions as follows: • Boldface indicates commands and keywords that are entered literally as shown. In actual configuration examples and output (not general command syntax), boldface indicates commands that are manually input by the user (such as a show command). • Italics indicate arguments for which you supply actual values. • Vertical bars (|) separate alternative, mutually exclusive elements. Note, however, that the vertical bar (pipe operand) is also used to filter command-line interface command output; in that scenario, the operand (|) precedes the begin, exclude, or include keywords, which are then followed by a regular expression. • Square brackets [ ] indicate optional elements. • Braces { } indicate a required choice. • Braces within brackets [{ }] indicate a required choice within an optional element. PC PC with Software Sun Workstation Macintosh Terminal File Server Web Server Cisco Works Workstation Printer Laptop IBM Mainframe Front End Processor Cluster Controller Modem DSU/CSU Router Bridge Hub DSU/CSU Catalyst Switch Multilayer Switch ATM Switch ISDN/Frame Relay Switch Communication Server Gateway Access Server Network Cloud Token Ring Token Ring Line: Ethernet FDDI FDDI Line: Serial Line: Switched Serial
xv Foreword The phrase “IP QoS” was for many years considered an oxymoron. Indeed, much of the success of the IP architecture could be traced to its adoption of a "best effort" service model, enabling IP to run over just about any underlying network technology. Best effort service, however, is defined by a lack of assurance that packets will be delivered in a timely manner, or even delivered at all. Such a service model limits the potential of IP networks to support applications that demand timely packet delivery, such as interactive telephony and multimedia applications. As far back as 1979, there were proposals to extend the IP service model to support applications with stronger QoS requirements. However, this remained a research topic until the early 1990s. By that point, the idea of convergence—carrying many applications with diverse QoS needs on a single network—was gaining currency, although the word “convergence” would not become a buzzword for several years. ATM was widely expected to be the packet switching technology that would enable this convergence, but a concerted effort to add QoS to IP was also getting underway. The seminal 1992 paper by Clark, Shenker, and Zhang on support of real-time applications in the Internet put a serious stake in the ground for IP QoS, and work at the IETF to standardize a set of IP QoS mechanisms began shortly thereafter. The Integrated Services architecture and Resource Reservation Protocol resulted, and the Differentiated Services architecture followed. Another technical development with big implications for IP QoS was Multiprotocol Label Switching, which grew out of work on Tag Switching at Cisco begun in 1996. There was considerable confusion about exactly what impact MPLS would have on IP QoS, in part because of the resemblances between MPLS and ATM, which had its own QoS model. In reality, the biggest single effect MPLS had on QoS was to add another tool to the QoS toolbox, in the form of traffic engineering with constraint-based rout- ing. It is for this reason more than any other that MPLS and QoS deserve to be covered in a single book. Which brings us to the current volume. IP QoS can now be considered a mature technology, not just something for the bleeding edge. It is also notoriously complex to understand and to configure cor- rectly. Some of this complexity is intrinsic; some is an accident of history. On the intrinsic side, under- standing QoS is hard because it requires the ability to operate at many different levels of abstraction. One needs to understand the high level QoS architectures, to have a behavioral model of QoS features inside a router, to know how those features map onto a particular piece of hardware, and to understand the CLI that is used to control those features. This is where this book sets itself apart from the pack of QoS books. Some cover QoS architecture and IETF standards. Some provide information on CLI com- mands. But this is the only book I've found that walks the reader through the levels of abstraction from high level architecture to low level CLI, with a clear explanation of the abstract QoS behavior model that all routers support providing the bridge between the levels. By reading this book, you will under- stand both the big picture of QoS and the details necessary to deploy it in a real network. Another factor that made QoS difficult to manage in the past was a somewhat ad hoc approach to its implementation. Combinations of features were sometimes implemented in a monolithic way, and inconsistency across platforms was the norm. This situation has improved massively in recent years, notably with the adoption of the Modular QoS CLI across most of the Cisco product line. Thus, QoS deployment is much more straightfoward than it once was, and this book's timely coverage of the MQC and its underlying behavioral model will make it even easier.
xvi Many readers may be tempted to jump straight to the last chapter's guidance on how to design and deploy a QoS strategy in a backbone network. Santiago's extensive real-world deployment experience certainly makes this chapter especially valuable. However, the preceding four chapters are the ones that will provide you with a fundamental understanding of QoS. Thus, rather than blindly following a QoS "recipe," you'll be able to make the right design decisions to meet the needs of your own applications and customers. If you really want to understand QoS fully, this is the book to read, from start to finish. Bruce Davie Cisco Fellow .
xvii Introduction The motivation behind this book is the continued interest in the implementation of quality of service (QoS) in IP/MPLS networks. QoS arises as a key requirement for these networks, which have become the preferred technology platform for building converged networks that support multiple services. The topic can be one of the most complex aspects of the network design, implementation, and operation. Despite the importance of and interest in this topic, no other Cisco Press title provides a detailed discus- sion of this subject. A significant amount of the content of this book also applies to pure IP networks that do not have immediate plans to migrate to a full IP/MPLS network. This material covers both QoS and Multiprotocol Label Switching Traffic Engineering (MPLS TE). In particular, it covers MPLS TE as a technology that complements traditional QoS technologies. MPLS TE can be an instrumental tool to improve the QoS guarantees that an IP/MPLS network offers. As such, it can contribute to improving both network performance and availability. However, this book pro- vides a concise discussion of MPLS TE. Those readers interested in further information should consult the Cisco Press title Traffic Engineering with MPLS. The book takes the point of view of those individuals responsible for the IP/MPLS network. Other Cisco Press titles describe the details of the QoS implementation for those devices receiving the services that the network offers. You should have a basic understanding of both IP and MPLS to obtain the most benefit from this book. That understanding should include basic IP addressing and routing, along with the basics of MPLS for- warding. However, the book provides a technology overview of QoS and MPLS TE to help those with less exposure to these technologies or to serve as a review/reference to those more familiar with those topics. This book touches a broad topic and does not pretend to address all QoS aspects of interest. You can expect future Cisco Press books to cover important areas, including the following: • Implementation of QoS for specific services (for instance, IP, Ethernet, ATM) • QoS management (including monitoring and provisioning) • Interprovider QoS Visit this book’s website, http://www.ciscopress.com/title/1587052334, for further information.
xviii Who Should Read This Book? This book’s primary audience is the technical staff of those organizations building IP/MPLS networks as an infrastructure to provide multiple services. The material includes technology, configuration, and operational details to help in the design, implementation, and operation of QoS in IP/MPLS networks. Service providers are a prime example of the organizations that this book targets. However, government agencies, educational institutions, and large enterprises pursuing IP/MPLS will find the material equally useful. A secondary audience for this book is those individuals in charge of service definition or those individu- als subscribing to network services. Both types can benefit from a better understanding of the differenti- ation capabilities that IP/MPLS networks can offer. How This Book Is Organized Although this book could be read cover to cover, it is designed to be flexible and allow you to easily move between chapters and sections of chapters to cover just the material that you need more work with. The content is roughly divided into three parts: • Chapters 1 and 2 provide a technology overview. • Chapters 3 and 4 discuss Cisco implemenation. • Chapter 5 covers different backbone design options. Here is a brief synopsis of each chapter: Chapter 1, “QoS Technology Overview”—This chapter provides a review of QoS technology for IP and IP/MPLS networks. The chapter initially discusses the IP QoS architectures and how they apply to MPLS. Multiple sections elaborate on MPLS support for Differentiated Services (DiffServ), including a detailed discussion on EXP-inferred-class link switched path (E-LSP), Label-inferred-class LSP (L- LSP), and DiffServ tunneling models (pipe, short pipe, and uniform). This dicussion leads into a sum- mary of traffic-management mechanisms with a detailed look at traffic policing, traffic shaping, traffic scheduling, active queue manangemt, and so on. The chapter also discusses QoS signaling with a focus on the Resource Reservation Protocol (RSVP). Chapter 2, “MPLS TE Technology Overview”—This chapter reviews the basic operation of this tech- nology with its DiffServ extensions and applicability as a traffic-protection alternative. This review elaborates on the concepts of contraint-based routing, DiffServ-aware Traffic Engineering (DS-TE) and fast reroute (FRR) (including link, shared-risk link group, and node protection). Chapter 3, “Cisco QoS”—This chapter covers the Cisco QoS behavioral model and the modular QoS command-line interface (MCQ). The chapter abstracts the platform specifics to facilitate the under- standing of Cisco QoS and provides a complete reference of the configuration commands. In addition, the chapter includes numerous examples to illustrate the configuration and verification of different traf- fic-management mechanisms in Cisco IOS and Cisco IOS XR. This material is equially relevant to IP and IP/MPLS networks.
xix Chapter 4, “Cisco MPLS Traffic Engineering”—This chapter presents Cisco implementation of MPLS Traffic Engineering in both Cisco IOS and Cisco IOS XR. It includes multiple configuration and verification examples illustrating the implementation of basic MPLS TE, DS-TE, and FRR. Chapter 5, “Backbone Infrastructure”—This chapter discusses the backbone performance require- ments and the different design options. The chapter reviews different designs, ranging from a best-effort backbone to the most elaborate scenarios combining DiffServ, DS-TE, and FRR. Numerous configura- tion examples illustrate their implementation using Cisco IOS and Cisco IOS XR.
C H A P T E R 1 QoS Technology Overview In this chapter, you review the following topics: • IP QoS Architectures • MPLS Support for IntServ • MPLS Support for DiffServ • Traffic-Management Mechanisms • QoS Signaling This chapter provides a review of the key technology components of quality of service (QoS) in IP/MPLS networks. This review discusses the IntServ and DiffServ architectures including their relationship with MPLS. The chapter covers the traffic management mechanisms that enable QoS implementation and reviews different QoS signaling alternatives in IP/MPLS with a special focus on RSVP protocol. This book assumes that you are already familiar with the basic concepts behind these topics. You should also be familiar with the basics of Multiprotocol Label Switching (MPLS) in general. This chapter and Chapter 2, “MPLS TE Technology Overview,” serve as a technology review and quick reference for later content. Chapter 3, “Cisco QoS,” covers the specifics on Cisco implementation of QoS technology. The “References” section at the end of this chapter lists sources of additional information on the topics that this chapter covers. IP QoS Architectures Originally, IP was specified a best-effort protocol. One of the implications of this service definition was that the network would attempt to deliver the traffic to its destination in the shortest time possible. However, the network would provide no guarantee of achieving it. This service definition proved successful during the early Internet years, when data applications constituted the bulk of Internet traffic. Generally, these applications used TCP and therefore adapted gracefully to variations in bandwidth, latency, jitter, and loss. The amount of interactive traffic was minimal, and other applications requiring stricter guarantees were at an experimental stage.
4 Chapter 1: QoS Technology Overview However, a new generation of applications with new service requirements emerged as the Internet grew in success. The increasing reach and capacity of the Internet made it an attractive infrastructure to support an increasing number of applications. In addition, corporations, governments, and educational institutions, among others, found the IP protocol an appealing option to build their private data networks. Many of the new IP applications (for example, voice and video) had a real-time nature and limited tolerance to variations in bandwidth, latency, jitter, and loss. The service expectations of network users and their application requirements made the best-effort service definition insufficient. The definition of a QoS architecture started in the middle of the 1990s. Since then, the Internet Engineering Task Force (IETF) has defined two QoS architectures for IP: Integrated Services (IntServ) and Differentiated Services (DiffServ). The IntServ architecture was the initial proposed solution. Subsequently, the DiffServ architecture came to life. MPLS later incorporated support for the DiffServ architecture, which the IETF had defined exclusively for IP. These two architectures use different assumptions and take different approaches to bringing QoS to IP.Although sometimes considered opposite and competing architectures, they tend to complement each other. Moreover, the QoS mechanisms used ultimately to manipulate traffic are essentially the same in both architectures. Integrated Services The IntServ working group was responsible for developing the specifications of this architecture at the IETF. The group met for the first time during the twenty-ninth IETF in 1994. The architecture specifications have a close relationship with the work of the IntServ over Specific Link Layers (ISSLL) and the Resource Reservation Protocol (RSVP) working groups. The ISSLL working group defined the implementation of IntServ over different link-layer protocols (for example, Ethernet and ATM). The RSVP working group defined the RSVP protocol that the IntServ group selected as the signaling protocol. The three working groups collectively produced 32 RFCs, of which 24 are in the IETF standards track. The working groups eventually closed between the years 2000 and 2002. The IETF decided to modify the original Internet architecture to support real-time applications. The IETF considered simpler alternatives, but they offered less-complete solutions. For instance • Fair-queuing algorithms solved the unfairness between data and real-time applications, but they could not guarantee the delay and jitter. • The use of separate networks for separate services was less efficient due to the lower levels of statistical multiplexing. • Bandwidth overprovisioning was not a realistic solution when bandwidth was offered as a service.
IP QoS Architectures 5 • A simple priority mechanism could not prevent a growing number of real-time flows from causing degradation of all flows. • The rate and delay adaptation of real-time applications had limits, especially when no admission control was used. IntServ Terminology This section lists several important terms that IntServ introduces. The next two sections provide more detail about these abstractions: • Flow—An identifiable stream of packets that a network node associates with the same request for QoS. A flow may span a single or multiple application sessions. • Traffic specification (TSpec)—Characterization of the traffic pattern of a flow over time. • Service request specification (RSpec)—Characterization of the QoS a flow desires. • Flow specification (flowspec)—Combination of a TSpec and an RSpec. Network nodes use the flowspec as input for admission-control decisions. Architecture Principles A crucial principle of the IntServ architecture is the requirement for resource reservation. This requirement implies admission control to manage finite resources. IntServ nodes need to avoid accepting unauthorized requests or requests that can affect existing reservations with service commitments. Different types of users are expected to have different rights to reserve network resources. In addition, the network load has to be controlled to meet the quantitative specification of the service-quality commitments of existing flows. IntServ leaves the selection of the QoS to the application rather than the network. The architecture defines a flow as the basic service unit. This abstraction represents a distinguishable stream of packets that requires the same QoS. Flows are unidirectional. They have a single source and one or many destinations. IntServ requires the use of per- flow state in network nodes. This requirement results from the flow granularity and the use of resource reservation with admission control. Having network nodes maintaining per- flow state represents a significant change to the original IP architecture that left per-flow state to end systems. The architecture recommends the use of a signaling protocol to set up and refresh the state to preserve the robustness of the IP protocol. RFC 1633 introduces the architecture. Figure 1-1 shows a simple example of an IntServ network.
6 Chapter 1: QoS Technology Overview Figure 1-1 Overview of a Network Implementing IntServ Service Model The IntServ architecture defines an extensible service model with a common framework. An important component of the definition of a service is the information that the receiver, which requests the service, must specify to the network.A service request includes a TSpec and, possibly, an RSpec. When a service request is accepted, the network nodes must guarantee the service as long as the TSpec continues to describe the flow. The combination of a TSpec and an RSpec receives the name of flowspec. The architecture service model uses a common TSpec definition. Four parameters characterize the traffic: • A token bucket (r, b)—The token bucket includes a token rate (r) and a token bucket size (b). • A peak rate (p)—Flow traffic may not arrive at a rate higher than the peak rate. • A minimum policed unit (m)—Network nodes treat packets of a size smaller than the minimum policed unit as packets of size m. This term facilitates the estimation of the actual bandwidth that a flow requires (including the Layer 2 header overhead). • A maximum packet size (M)—A node considers packets with a size larger than M as packets that do not conform to the traffic specification. Those nonconforming packets might not receive the same service as conforming packets. RSVP Endpoint RSVP Endpoint Flow Signaling Message RSVP State RSVP State RSVP State Signaling Message
IP QoS Architectures 7 Table 1-1 summarizes the TSpec parameters. NOTE The token bucket is an important concept in traffic management. The sections “Traffic Policing” and “Traffic Shaping” describe it in more detail later in this chapter. The architecture defined two services: Guaranteed Service (GS) and Controlled Load Service (CLS). They complement the best-effort service that is part of the definition of the IP protocol. IntServ does not introduce any changes to the operation of the best-effort service. In addition, the IntServ service model does not mandate a particular implemen- tation for the traffic-management mechanisms that implement a service. The next two sections explain the GS and CLS services, focusing on their end-to-end behavior and their flow specifications. NOTE RFC 2997 later defined a Null Service type. Applications can use this service to let the network determine the appropriate service parameters for the flow. This service type has special applicability for the integration of IntServ and DiffServ architectures. Guaranteed Service GS provides flows with a delay and bandwidth guarantee. GS ensures a firm bound on the maximum end-to-end queuing delay for packets that conform to the flowspec. Furthermore, a properly policed flow should not experience queuing drops in the absence of network failures or routing changes. The service does not consider fixed-delay components that are a property of the flow path (for example, propagation delay or serialization delay). A flow receives guaranteed service if all nodes along the path support the service. GS does not guarantee an average or minimum delay, just a maximum bound. Therefore, this service does not provide any jitter guarantees. RFC 2212 defines GS. Table 1-1 TSpec Parameters Parameter Description r Token rate b Token bucket size p Peak rate m Minimum policed unit M Maximum packet size
8 Chapter 1: QoS Technology Overview A receiver provides a TSpec and an RSpec when requesting GS. The RSpec contains a service rate (R) and a time slack (S). Network nodes must approximate the service that a dedicated line at that rate would provide to the flow. Nodes make available the margin of error of their approximation. Applications can use this information to compute the maximum end-to-end delay that the flow will experience. The slack term in the RSpec specifies the incremental end-to-end delay that the sender can tolerate if a node modifies the flow resource allocation. Applications can adjust the flowspec if the delay bound is not acceptable. Table 1-2 summarizes the RSpec parameters. Control Load Service CLS approximates the behavior of best-effort service during unloaded conditions. Network nodes satisfy this behavior even in the presence of congestion.Applications can assume that the network will deliver a high percentage of all packets to their final destination. In addition, applications can assume that a high percentage of the delivered packets will experience a delay that will not greatly exceed the minimum delay of any packet. Applications do not receive any target values for packet delay or loss. This service supports those applications that operate satisfactorily with a best-effort service but are highly sensitive to congestion conditions. Applications do not require an RSpec to request CLS, only the flow TSpec. RFC 2211 introduces CLS. Use of RSVP in IntServ IntServ can use RSVP as the reservation setup protocol. One of the principles of this architecture is that applications communicate QoS requirements for individual flows to the network. These requirements are used for resource reservation and admission control. RSVP can perform this function. However, RSVP is frequently but inaccurately equated to IntServ. RSVP and IntServ share a common history, but they are ultimately independent. Two separate working groups at the IETF developed their specifications. RSVP has applicability as a signaling protocol outside IntServ. Similarly, IntServ could use other signaling mechanisms. The section “Resource Reservation Protocol” explains the protocol details later in this chapter. RFC 2210 describes how IntServ uses RSVP and defines the RSVP objects to implement the IntServ service model. Table 1-2 RSpec Parameters Parameter Description R Service rate S Time slack
IP QoS Architectures 9 Differentiated Services The DiffServ working group was responsible for the definition of this architecture at the IETF. The group met for the first time during the forty-first IETF in 1998. The working group was created with a charter to produce an architecture with a simple and coarse QoS approach that applied to both IPv4 and IPv6. The charter explicitly excluded microflow identification and signaling mechanisms (marking an explicit departure from the approach taken by IntServ). The working group produced 12 RFCs, with five of them being in the standards track and the rest being informational. The group eventually closed after its last meeting in 2001. NOTE An IP traffic stream with a unique combination of source address, destination address, protocol, source port, and destination port defines a microflow. DiffServ Terminology The DiffServ architecture introduces many new terms. This section presents a simplified definition of a selected few of them. The upcoming sections explain the terms in more detail. RFC 2475 and 3260 introduce the complete list of terms: • Domain—A network with a common DiffServ implementation (usually under the same administrative control). • Region—A group of contiguous DiffServ domains. • Egress node—Last node traversed by a packet before leaving a DiffServ domain. • Ingress node—First node traversed by a packet when entering a DiffServ domain. • Interior node—Node in a DiffServ domain that is not an egress or ingress node. • DiffServ field—Header field where packets carry their DiffServ marking. This field corresponds to the six most significant bits of the second byte in the IP header (formerly, IPv4 TOS [Type-of-Service] octet and IPv6 Traffic Class octet). • Differentiated Services Code Point (DSCP)—A specific value assigned to the DiffServ field. • Behavior aggregate (BA)—Collection of packets traversing a DiffServ node with the same DSCP. • Ordered aggregate (OA)—A set of BAs for which a DiffServ node must guarantee not to reorder packets. • BA classifier—Classifier that selects packets based on DSCP. • Multifield (MF) classifier—Classifier that selects a packet based on multiple fields in the packet header (for example, source address, destination address, protocol, and protocol port).
10 Chapter 1: QoS Technology Overview • Per-hop behavior (PHB)—Forwarding behavior or service that a BA receives at a node. • Per-hop behavior group—One or more PHBs that are implemented simultaneously and define a set of related forwarding behaviors. • PHB scheduling class (PSC)—A set of PHBs for which a DiffServ node must guarantee not to reorder packets. • Traffic profile—Description of a traffic pattern over time. Generally, in terms of a token bucket (rate and burst). • Marking—Setting the DSCP in a packet. • Metering—Measuring of a traffic profile over time. • Policing—Discarding of packet to enforce conformance to a traffic profile. • Shaping—Buffering of packets to enforce conformance to a traffic profile. • Service level agreement (SLA)—Parameters that describe a service contract between a DiffServ domain and a domain customer. • Traffic-conditioning specification—Parameters that implement a service level specification. • Traffic conditioning—The process of enforcing a traffic conditioning specification through control functions such as marking, metering, policing, and shaping. NOTE This DiffServ section is consistent with the original architecture terms. Note, however, that Cisco documentation considers metering an implicit component of traffic shaping and policing. Furthermore, it regards dropping as just one of three possible actions (transmit, drop, mark) of a policer. The remainder of the book follows the policing and shaping definitions used in Cisco documentation. Architecture Principles The DiffServ architecture relies on the definition of classes of traffic with different service requirements. A marking in the packet header captures the traffic classification. Further network nodes inspect this marking to identify the packet class and allocate network resources according to locally defined service policies. The service characteristics are unidirectional with a qualitative description in terms of latency, jitter, and loss. DiffServ nodes are stateless from a QoS point of view and have no knowledge of individual flows. Relatively few packet markings are possible with respect to the number of microflows that a node may be switching at a given point in time. However, the concept of grouping or aggregating traffic into a small number of classes is inherent to DiffServ. The architecture intentionally makes a tradeoff between granularity and scalability. RFC 2475 introduces the architecture.
IP QoS Architectures 11 Providing different levels of service using aggregate classification and marking is not a novel concept. As an analogy, consider a transoceanic commercial flight with multiple classes of service. During the check-in process, the passenger needs to provide some identification information (classification criteria). Based on this information, the agent identifies the passenger class (for instance, first, business, or tourist) and provides a boarding pass that reflects the assigned class (marking). The customer class influences the service the passenger receives during the duration of the flight (including access to airline lounge, boarding priority, in-flight service, and deboarding priority). The reduced number of classes allows the airline to provide some differentiation to customers without having to provide a totally individualized service to each passenger. As you can probably recognize, this is not the only instance of aggregate classification and marking used in real life. Differentiated Services Code Point Previous specifications of the IP protocol had already reserved header bits for QoS purposes. The IP version 4 specifications in RFC 791 defined the second header octet as the TOS octet. Also, the IP version 6 specifications in RFC 2460 defined the second header octet as the Traffic Class octet but with an undefined structure. In the original TOS octet in IP version 4, the three most significant bits specified the packet precedence (an indication of the relative importance or priority). The next 3 bits in the TOS octet indicated the delay, throughput, and reliability requirements. The final two (least significant) bits were undefined and set to zero. RFC 1349 introduced a small change in the TOS octet by defining a field that included a cost bit plus the existing delay, throughput, and reliability bits. Similarly, the IP version 6 specifications in RFC 2460 define the second header octet as the Traffic Class octet but with an undefined structure. Figure 1-2 illustrates these now-obsolete definitions. The DiffServ architecture redefines the IPv4 TOS octet and the IPv6 Traffic Class octet. RFC 2474 and RFC 3260 name the DiffServ field as the six most significant bits in the previous IPv4 TOS and IPv6 Traffic Class octets. A particular value of the DiffServ field represents a DSCP. A DiffServ node services packets according to this code point. A group of packets sharing the same DSCP and traversing a link in a specific direction constitutes a BA. A class of traffic may include one or more BAs. The architecture defines three code point pools for the DiffServ field. Two pools, representing 32 out of the 64 possible values, are reserved for experimental or local use. The existing DiffServ specifications provide recommendations for 21 out of the 32 code points available in the third pool. The section “Per-Hop Behaviors” in this chapter introduces these values and their service definitions. Eight (class selector) code points provide backward compatibility with the previous Precedence field in the TOS octet. The DiffServ field does not provide any backward compatibility with the TOS field (delay, throughput, and reliability bits) previously defined in the TOS octet. Figure 1-3 shows the structure of the new DiffServ field, the code point pools, and the class selector code points.
12 Chapter 1: QoS Technology Overview Figure 1-2 Previous Definitions of the TOS Octet for IPv4 and IPv6 That DiffServ Makes Obsolete Figure 1-3 DiffServ Field, Code Point Pools, and Class Selector Code Points Precedence D 0 1 2 3 4 5 6 7 T R 0 0 RFC 791 Precedence 111 – Network Control 110 – Internetwork Control 101 – CRITIC / ECP 100 – Flash Override 011 – Flash 010 – Immediate 001 – Priority 000 – Routine Delay (D) 0 – Normal 1 – Low Throughput (T) 0 – Normal 1 – High Reliability (R) 0 – Normal 1 – High T r a f f i c c l a s s 0 1 2 3 4 5 6 7 RFC 2460 Precedence 0 1 2 3 4 5 6 7 T O S 0 RFC 1349 Precedence 111 – Network Control 110 – Internetwork Control 101 – CRITIC / ECP 100 – Flash Override 011 – Flash 010 – Immediate 001 – Priority 000 – Routine TOS Field 1000 – minimize delay 0100 – maximize throughput 0010 – maximize reliability 0001 – minimize monetary cost 0000 – normal service D i f f S e r v F i e l d 0 1 2 3 4 5 6 7 RFC 2474 RFC 3260 DiffServ Field Codepoint Pools xxxxx0 – Standard xxxx11 – Experimental or local use xxxx01 – Future standard, experimental or local use DiffServ Codepoints 111000 – Class Selector 7 110000 – Class Selector 6 101000 – Class Selector 5 100000 – Class Selector 4 011000 – Class Selector 3 010000 – Class Selector 2 001000 – Class Selector 1 000000 – Class Selector 0
IP QoS Architectures 13 Nodes, Domains, and Regions The DiffServ architecture defines a hierarchy that goes from a single device, to a network, to a group of networks. A set of nodes with a common DiffServ implementation forms a domain. The nodes inside a domain perform similar service definitions and policies. A domain is typically under a single administrative control. A set of contiguous domains defines a DiffServ region. The domains within the region must be able to provide DiffServ to traffic traversing the different domains in the region. Individual domains may use different service definitions, policies, and packet markings. In those cases, the domains must have peering agreements that specify how traffic is handled when crossing domains. Boundary nodes and interior nodes constitute the two main types of nodes that reside in a DiffServ domain. Boundary nodes interface with the outside of the domain and ensure that any traffic is properly classified, marked, and within the agreed amounts. DiffServ defines these operations as traffic classification and conditioning. Boundary and interior nodes implement local service policies according to the packet marking. These local policies provide different levels of service to each BA that DiffServ calls PHBs. The section “Per- Hop Behaviors” discusses this concept in detail. A domain may have some nodes that do not support DiffServ. The service impact of these nodes depends on their number and their location within a domain. Figure 1-4 illustrates a DiffServ region with two domains. Traffic enters a domain at an ingress boundary node and leaves the domain at an egress boundary node. The ingress boundary node typically performs the traffic-classification and conditioning function according to a specification or contract. Boundary nodes generally act as both ingress and egress nodes because traffic differentiation is desirable for the traffic that flows in both directions. Traffic Classification and Conditioning Traffic classification and conditioning identifies the traffic that will receive a differentiated service and ensures that it conforms to a service contract. Outside nodes connecting to the DiffServ domain have agreed to some service terms that the architecture defines as an SLA. The boundary node enforces this SLA, or contract, using traffic classification and conditioning. This enforcement uses a combination of packet classification, marking, metering, shaping, and policing to ensure that the traffic conforms to the contract terms.
14 Chapter 1: QoS Technology Overview Figure 1-4 Functional View of Nodes and Domains in a DiffServ Region NOTE RFC 3260 refined the initial DiffServ definition of SLA and introduced a new term, service level specification (SLS). Even though the term clarification is useful, this book uses the term SLA (which is more commonly used). Traffic classification is the first action that a boundary node performs on traffic entering the domain. The boundary node examines the packet and, according to the SLA terms, implements an appropriate action (for example, marking, metering, policing). The architecture describes two types of classifiers: BA classifier and MF classifier. The BA classifier classifies packets using the DSCP in the packet. The MF classifier classifies packets using one or more fields of the packet header (for example, source IP address, destination IP address, protocol, source port, destination port) and other packet information (for example, input interface). The final result of packet classification is the local association of each packet with a class. NOTE The DiffServ architecture did not consider packet payload as input for packet classification. Actual implementations support packet classification using payload inspection and other classification criteria.You can consider those classifiers as an extension of the MF classifiers. Region Direction of Traffic Flow Ingress Boundary Node Egress Boundary Node Interior Node Upstream Domain Downstream Domain Ingress Boundary Node Egress Boundary Node Interior Node
IP QoS Architectures 15 The boundary node conditions packets according to the SLA after classification. Traffic conditioning involves a combination of one or more of the following mechanisms: metering, marking, policing, or shaping. This conditioning process uses the result of the packet classification as input. Conditioning may vary from class to class. SLAs typically define a limit on the amount of traffic that the boundary node will take for each class. In those cases, the boundary node measures the traffic and makes a marking, dropping, or buffering decision on the packet. Conditioning must set the DSCP of each packet to an appropriate value. Downstream nodes typically rely on this DSCP for fast packet classification. The sections “Traffic Policing” and “Traffic Shaping” provide more details on conditioning mechanisms. Traffic classification and conditioning may happen at different points of a packet path. In general, boundary nodes perform these tasks. However, the architecture does not preclude interior nodes from doing complex classification and conditioning if needed (for example, on international links). Figure 1-5 shows an example in which the ingress boundary node of the upstream domain uses MF classifiers and conditions separately the traffic that A and B generate. Marking packets close to the source facilitates application differentiation and simplifies classification on downstream nodes. In this example, the ingress boundary node of the downstream domain conditions the aggregate traffic that it receives. The ingress node relies on the classification and marking that the upstream domain performed. The egress boundary nodes may also perform traffic conditioning. Figure 1-5 Illustration of SLA Enforcement Across Two DiffServ Domains Per-Hop Behaviors The DiffServ architecture defines a PHB as the forwarding behavior that a node applies to a BA. It represents a qualitative description of the latency, jitter, or loss characteristics that a BA will experience while traversing a DiffServ node. The PHB definition does not BA classification and aggregate conditioning enforce SLA between domains MF classification and conditioning enforce a separate SLA for each source. A B Ingress Boundary Node Egress Boundary Node Upstream Domain Downstream Domain Ingress Boundary Node Egress Boundary Node IP
16 Chapter 1: QoS Technology Overview quantify these characteristics. A PHB group contains one or more related PHBs that are implemented simultaneously. DiffServ nodes map packets to PHBs according to their DSCP. Table 1-3 shows the mappings that the architecture specifications recommend. DiffServ does not mandate these DSCP-to-PHB mappings. It provides the flexibility to confiugure arbitrary mappings if desired. Class selectors are the only exception, because the architecture defines them for backward compatibility with the use of the Precedence field in the IPv4 TOS octet. DiffServ domains not using the recommended mappings are more likely to have to re-mark traffic when interfacing with other DiffServ domains and experience greater operational complexity. Table 1-3 IETF-Recommended Mapping Between PHBs and DSCPs PHB DSCP (Decimal) DSCP (Binary) EF 46 101110 AF43 38 100110 AF42 36 100100 AF41 34 100010 AF33 30 011110 AF32 28 011100 AF31 26 011010 AF23 22 010110 AF22 20 010100 AF21 18 010010 AF13 14 001110 AF12 12 001100 AF11 10 001010 CS7 56 111000 CS6 48 110000 CS5 40 101000 CS4 32 100000 CS3 24 011000 CS2 16 010000 CS1 8 001000 Default 0 000000
IP QoS Architectures 17 A number of PHB or PHB groups are part of the current DiffServ specifications: Expedited Forwarding (EF), Assured Forwarding (AF1, AF2, AF3, and AF4), Class Selector (CS), and Default. A node may support multiple PHB groups simultaneously. Nodes implement these PHBs using packet-buffering and scheduling mechanisms that the section “Traffic- Management Mechanisms” discusses. Expedited Forwarding The EF PHB defines a low-latency, low-jitter, and low-loss behavior that a DiffServ node may implement. This PHB acts as a building block for the transport of real-time traffic over a DiffServ domain. To support this behavior, a DiffServ node must serve EF traffic at a rate that is higher than its arrival rate, independently of the amount of non-EF traffic. This difference between the EF arrival and service rate helps ensure that EF traffic encounters empty or near-empty queues, which minimizes the queuing latency. This type of latency is generally the main contributor to packet latency and jitter during normal node operation. Minimization of queuing latency results in not only low latency and low jitter but also in low loss, because it prevents exhaustion of packet buffers. A DiffServ node should not cause any packet reordering within EF microflows. RFC 3246 and RFC 3247 define and discuss this PHB in detail. Assured Forwarding The AF family of PHB groups defines four different levels of forwarding guarantee that a DiffServ node may support. In simpler terms, these groups define how a DiffServ node may support different packet-loss guarantees. TheAF PHB groups receive the names:AF1,AF2, AF3, and AF4. Each of these groups supports three drop-precedence levels. The higher the drop precedence, the more likely a DiffServ node will drop the packet if the group exhausts its allocated resources (bandwidth and buffers). A total of 12 PHBs are associated with AF. Table 1-4 lists these PHBs with their respective drop precedence. RFC 2597 provides the detailed specifications for this set of PHB groups. The AF PHB groups operate independently of each other. No implied ordering of forwarding guarantee exists between them. Furthermore,AF groups do not have an implicit latency or jitter characterization. The actual guarantees provided by each group depend on the forwarding resources that the node allocated, the amount of traffic of that group arriving Table 1-4 AF PHBs and Their Respective Drop Precedence Drop Precedence AF1 AF2 AF3 AF4 Low AF11 AF21 AF31 AF41 Medium AF12 AF22 AF32 AF42 High AF13 AF23 AF33 AF43
18 Chapter 1: QoS Technology Overview at the node, and the relative drop precedence of the packet. The resources the node allocates are bandwidth and buffering space. The specifications mandate that nodes forward with higher probability those packets within an AF group that have lower drop precedence. A DiffServ node must not reorder packets of the same microflow within an AF group. Class Selectors DiffServ defines CS PHBs to offer backward compatibility with the use of IP precedence in the IPv4 TOS octet. Class selectors maintain the same relative ordering of IP precedence (a higher value implies a higher relative order). A node should provide a higher probability of forwarding to higher CSs. There is no latency, jitter, or loss characterization. Table 1-5 shows the mapping between CSs and IP precedence. Default PHB A DiffServ domain must provide a Default PHB that offers best-effort service. More precisely, the architecture defines the Default PHB as the existing best-effort service that RFC 1812 specifies. That is, the DiffServ domain will forward as many packets as possible, as soon as possible. There is no latency, jitter, and loss characterization. The implementation of other PHBs should preclude the operation of applications that rely on best-effort service. MPLS Support for IntServ MPLS support for IntServ remains undefined. The fact that RSVP can perform MPLS label distribution does not imply support for IntServ. As mentioned previously, the IntServ architecture makes use of RSVP, but the protocol signaling capabilities go beyond the IntServ requirements. However, you can find current efforts at the IETF to specify the Table 1-5 Relationship Between IP Precedence Values and DiffServ CSs PHB DSCP (Decimal) DSCP (Binary) Precedence Name Precedence (Binary) Precedence (Decimal) CS7 56 111000 Network Control 111 7 CS6 48 110000 Internetwork Control 110 6 CS5 40 101000 Critic/ECP 101 5 CS4 32 100000 Flash Override 100 4 CS3 24 011000 Flash 011 3 CS2 16 010000 Immediate 010 2 CS1 8 001000 Priority 001 1 CS0 0 000000 Routine 000 0
MPLS Support for DiffServ 19 interaction of aggregate IntServ reservations with MPLS networks. This proposal allows aggregate reservations to take advantage of the capabilities of MPLS networks without forcing those networks to provide full IntServ support. The “References” section at the end of this chapter lists reading material on the subject that currently constitutes work in progress. MPLS Support for DiffServ MPLS supports DiffServ with minimal adjustments to the MPLS and DiffServ architectures. MPLS does not introduce any modifications to the traffic-conditioning and PHB concepts defined in DiffServ. A label switching router (LSR) uses the same traffic-management mechanisms (metering, marking, shaping, policing, queuing, and so on) to condition and implement the different PHBs for MPLS traffic. An MPLS network may use traffic engineering to complement its DiffServ implementation. RFC 3270 defines MPLS support for the DiffServ architecture. An MPLS network may implement DiffServ to support a diverse range of QoS requirements and services in a scalable manner. MPLS DiffServ is not specific to the transport of IP traffic over an MPLS network. An MPLS network may be carrying other types of traffic for which DiffServ does not apply (for example, ATM or Frame Relay). An MPLS DiffServ implementation is concerned only with supporting the PHBs that can satisfy the QoS requirements of all the types of traffic it carries. In addition, an MPLS network can grow without having to introduce major changes to its DiffServ design as the number of label switched paths (LSPs) in the network increases. These characteristics play an important role in the implementation of large MPLS networks that can transport a wide spectrum of traffic. MPLS support for DiffServ introduces two types of LSPs with different service characteristics and operation. The first type, EXP-inferred-class LSP (E-LSP), can transport simultaneously multiple classes of traffic. The second type, Label-inferred-class LSP (L-LSP), transports a single class. They rely on different mechanisms to encode the DiffServ marking of the packet. In general, MPLS uses a label stack encoding based on shim headers that RFC 3032 defines. Figure 1-6 illustrates the fields contained in the shim header. The specifications for MPLS DiffServ define two encodings for the DiffServ code point. In addition, these LSP types impose different LSP signaling requirements. The changes in the encoding of DiffServ marking and the use of signaling are the two important areas where MPLS DiffServ differs from the original specification. NOTE RFC 3270 formally defines E-LSPs as EXP-inferred-PSC LSPs and L-LSP as Label-only- inferred-PSC LSPs. The section “DiffServ Terminology” provided a formal definition of a PSC earlier in this chapter. You can simply equate the term to a class of traffic.
20 Chapter 1: QoS Technology Overview Figure 1-6 MPLS Shim Header NOTE ATM LSRs, Frame Relay LSRs, and LSRs with label switching controlled ATM (LC-ATM) interfaces use a native encoding for the top label rather than the shim header. This has important implications for the implementation of DiffServ on those devices. Given their decreasing use, this book does not focus on their details. E-LSP MPLS support for DiffServ defines E-LSP as a type of LSP that can carry simultaneously multiple classes of traffic. LSRs use the EXP field in the shim header to infer the PHB that a packet requires. As Figure 1-6 shows, the EXP contains three bits that can take eight possible values. The size of this field implies that an E-LSP can transport up to eight classes of service. An E-LSP carries fewer classes if some of those classes consume multiple markings (for example, AF1 which may use two or three markings). The specifications do not define recommended EXP values for the existing DiffServ PHBs (EF, AFn, CSn, Default). Furthermore, they do not define any structure on the three-bit field. LSRs may set up E-LSPs with bandwidth reservation (generally for the purpose of admission control). Figure 1-7 illustrates a network using E-LSPs. In this case, there are two E-LSPs between node A and D. The network supports three classes: EF, AF1, and AF2. From top to bottom, the first E-LSP carries EF traffic; the second LSP multiplexes traffic of the three classes. Even though E-LSPs may carry multiple classes, the first E-LSP transports only EF traffic in this scenario.According to the E-LSP rules, all nodes perform PHB determination based on the EXP value of the packet. Notice that some EF traffic follows one E-LSP, whereas the rest follows the other E-LSP. Node A can split EF traffic if the node does not split EF microflows. Node C serves EF traffic without consideration of what LSP carries the EF traffic. Label EXP TTL S 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 MPLS Shim Header Label: MPLS Label Value EXP: Experimental Use S: Bottom of Stack TTL: Time to Live RFC 3032
MPLS Support for DiffServ 21 Figure 1-7 MPLS Network Using an E-LSP MPLS support for DiffServ defines mechanisms for E-LSPs to signal mappings between EXP values and PHBs. An LSR associates EXP-to-PHB mappings for input labels and PHB-to-EXP mappings for output labels. Signaling is optional and takes place during LSP setup. RFC 3270 defines extensions to LDP (DiffServ TLV [Type, Length, Value] for Label Request, Label Mapping, Label Release, and Notification messages) and RSVP (DiffServ object for Path messages) and their appropriate processing. The signaling identifies the LSP as an E-LSP and specifies the mappings between EXP values and PHBs that it will use. LSRs can use static but configurable mappings to avoid these signaling extensions for E-LSPs. An LSR should map all EXP values to the Default PHB if the LSP signaling did not specify a mapping and no preconfigured mapping exists. NOTE ATM LSRs, Frame Relay LSRs, and LSRs with LC-ATM interfaces do not forward packets using an MPLS shim header encapsulation. The absence of a shim header implies the absence of the EXP field. Therefore, those devices cannot support E-LSPs. This restriction also applies to nonpacket networks that use generalized MPLS (GMPLS). IP/MPLS C B D A EF Packet AF1 Packet AF2 Packet
22 Chapter 1: QoS Technology Overview L-LSP MPLS support for DiffServ defines L-LSP as a type of LSP that can only transport of a single class of traffic. LSRs infer the class associated with the a packet from the label and determine the exact PHB using the label in combination with the EXP field. Table 1-6 illustrates the mandatory mapping between <classes, EXP> and PHBs. LSRs learn the association between L-LSP labels and classes during LSP setup. L-LSPs require the use of DiffServ signaling extensions. In this case, LSRs use a different format of the LDP DiffServ TLV and RSVP DiffServ object. The signaling identifies the LSP as an L-LSP and specifies the class that the L-LSP will transport. As with E-LSPs, LSRs may set up L-LSPs with bandwidth reservation. Table 1-6 Mandatory PHB Mappings for L-LSPs Class EXP (Decimal) EXP (Binary) PHB EF 0 000 EF AF4 3 011 AF43 AF4 2 010 AF42 AF4 1 001 AF41 AF3 3 011 AF33 AF3 1 010 AF32 AF3 3 001 AF31 AF2 2 011 AF23 AF2 1 010 AF22 AF2 3 001 AF21 AF1 2 011 AF13 AF1 1 010 AF12 AF1 1 001 AF11 CS7 0 000 CS7 CS6 0 000 CS6 CS5 0 000 CS5 CS4 0 000 CS4
MPLS Support for DiffServ 23 Figure 1-8 illustrates an MPLS network using L-LSPs. In this case, there are four L-LSPs between node A and D. The network supports three classes: EF, AF1, and AF2. From top to bottom, the first L-LSP carries AF2, the second and third ones carry EF, and the fourth and last L-LSP carries AF1 traffic. Notice that node A splits EF traffic over two L-LSPs. Node A can divide EF traffic if the node does not split EF microflows. Even though Node C identifies EF traffic using the labels, that node serves EF traffic without consideration of what L-LSP is carrying the traffic (that is, the node does not provide a PHB per L-LSP, but per class). Figure 1-8 MPLS Network Using L-LSPs The use of E-LSPs and L-LSPs on an MPLS network is not mutually exclusive. LSRs maintain a DiffServ label context. This context indicates the LSP type (E-LSP or L-LSP), the PHBs that the LSP supports, and a mapping between the packet encapsulation and a PHB. For input labels, that mapping defines how the LSR can infer the PHB from the packet encapsulation. For output labels, that mapping defines how the LSR encodes the PHB. This Class EXP (Decimal) EXP PHB CS3 0 000 CS3 CS2 0 000 CS2 CS1 0 000 CS1 Default 0 000 Default Table 1-6 Mandatory PHB Mappings for L-LSPs (Continued) IP/MPLS C B D A EF Packet AF1 Packet AF2 Packet
24 Chapter 1: QoS Technology Overview context is populated with preconfigured mappings or through DiffServ information learned during LSP setup. Table 1-7 compares E-LSPs and L-LSPs. Figure 1-9 shows an MPLS network using L-LSPs and E-LSPs simultaneously. In this example, there are two E-LSPs between node E and node D and two L-LSPs between node A and D. The network supports three classes: EF, AF1, and AF2. In this example, node C transports both E-LSPs and L-LSPs. This node uses the DiffServ label context to determine the LSP type and the exact mapping that it should use to infer the PHB from the packet encapsulation. LSRs serve the packets according to their PHB regardless of the LSP and its type. The LSP details influence the PHB determination, but the PHB ultimately determines the packet treatment. In this example, nodes A and E use one type of LSPs exclusively. However, each of them could alternatively use a combination of E-LSPs and L-LSPs to reach node D. Figure 1-9 MPLS Network Combining L-LSPs and E-LSPs Table 1-7 Comparing E-LSPs and L-LSPs E-LSP L-LSP One or more classes per LSP One class per LSP PHB inferred from EXP field PHB inferred from Label and EXP field Signaling optional Signaling required IP/MPLS C B D A E EF Packet AF1 Packet AF2 Packet E-LSP L-LSP
MPLS Support for DiffServ 25 NOTE ATM LSRs, Frame Relays LSRs, and LSRs with LC-ATM interfaces do not forward packets using an MPLS shim header encapsulation. The absence of a shim header implies the absence of the EXP field. However, those devices can still support DiffServ using their native encapsulation to implement L-LSPs.ATM LSRs and LSRs with LC-ATM interfaces use the native label encoding and the ATM CLP (Cell Loss Priority) bit for PHB determination. Frame Relay LSRs use their native label encoding and the Frame Relay DE bit for PHB determination. RFC 3270 describes in detail the procedures that apply in those cases. DiffServ Tunneling Models over MPLS MPLS LSPs support for DiffServ defines three models of interaction between DiffServ markings in different layers of encapsulation. A simple example is an IP packet that has received the MPLS encapsulation. There is one PHB marking in the MPLS encapsulation and a PHB marking in the DiffServ field of the IP packet. There are three models to handle the interaction between multiple markings: the pipe, short-pipe, and uniform models. The models define the procedures that an LSR can apply when a packet (either IP or MPLS) with an existing PHB marking enters and exits an LSP. The three models do not introduce any changes to the normal label swapping behavior of an LSR or any signaling requirements. These models apply equally to E-LSPs and L-LSPs. NOTE The MPLS DiffServ tunneling models extend the concepts introduced in RFC 2983. That RFC defines the operation of DiffServ over IP tunnels. In many aspects, LSPs resemble IP tunnels. NOTE RFC 3270 defines the MPLS DiffServ tunneling models for the transport of IP and MPLS traffic. However, the underlying concepts can apply to the transport of other types of traffic (for example, Ethernet) over an MPLS network. Pipe Model The pipe model conceals the tunneled PHB marking between the LSP ingress and egress nodes. This model guarantees that there are no changes to the tunneled PHB marking through the LSP; even if an LSR along the path performs traffic conditioning and re-marks the traffic. All LSRs that the LSP traverses use the LSP PHB marking and ignore the tunneled PHB marking. This model proves useful when an MPLS network connects other DiffServ domains. The MPLS network can implement DiffServ and still be transparent for the connected domains. RFC 3270 defines this model as mandatory for MPLS networks supporting DiffServ.
26 Chapter 1: QoS Technology Overview Figure 1-10 illustrates the operation of the pipe model. The LSP ingress determines the LSP PHB marking it will encode in the pushed encapsulation. It may consider the existing PHB marking of the packet for this purpose. It preserves the tunneled PHB marking when pushing the new label encapsulation. Be aware that the packet entering the LSP may be an IP or an MPLS packet. The LSP egress serves the packet according to the LSP PHB marking. This action implies that this node infers the packet PHB before the pop operation. Moreover, the LSP egress does not modify the tunneled PHB marking that the pop operation exposes. An LSP using the pipe model cannot use penultimate hop popping (PHP) because the LSP egress will not have access to the LSP PHB marking. Figure 1-10 Pipe Tunneling Model Short-Pipe Model The short-pipe model represents a small variation of the pipe model. It also guarantees that there are no changes to the tunneled PHB marking, even if an LSR re-marks the LSP PHB marking. The short-pipe model shares the same ability of the pipe model to allow an MPLS network to be transparent from the DiffServ point of view. The short-pipe model differs, however, on how the LSP egress infers the packet PHB. The LSP egress uses the tunneled PHB marking to infer the packet PHB and serve the packet consequently. Given this difference with the pipe model, an MPLS network may implement LSPs using the short- pipe model regardless of whether LSRs perform PHP. Label Label IP/MPLS LSP Ingress LSP Egress LSP PHB Marking IP or MPLS Packet Tunneled PHB Marking Push Pop LSP PHB Marking Defines Packet PHB
MPLS Support for DiffServ 27 Figure 1-11 demonstrates the details of the operation of the short-pipe model with PHP. The LSP ingress must determine the LSP PHB marking it will encode in the pushed encapsulation. It may consider the existing PHB marking of the packet. The LSP ingress also preserves tunneled PHB marking when pushing the new label encapsulation. The short-pipe and pipe models share the same procedure for the LSP ingress. It infers the packet PHB from the LSP PHB marking before performing the pop operation. The penultimate hop does not modify the tunneled PHB marking that the pop operation exposes. The LSP egress infers the packet PHB from the tunneled PHB marking in the header used for packet forwarding. Figure 1-11 Short-Pipe Tunneling Model with PHP Figure 1-12 shows the details of the short-pipe model for LSPs that do not experience PHP. The operation of the LSP ingress remains the same as before. The penultimate hop performs the label swapping operation and serves the packet according to the corresponding E-LSP or L-LSP procedures. The LSP egress infers the packet PHB from the tunneled PHB marking in the header used for packet forwarding. This action implies that the LSP egress infers the packet PHB after the label pop. As with all previous models, this node forwards the tunneled PHB marking unmodified. The short-pipe model offers the external behavior regardless of whether PHP happens. Label Label IP/MPLS LSP Ingress LSP Egress Penultimate Hop LSP PHB Marking IP or MPLS Packet Tunneled PHB Marking Push Pop LSP PHB Marking Defines Packet PHB Tunnel PHB Marking Defines Packet PHB
28 Chapter 1: QoS Technology Overview Figure 1-12 Short-Pipe Tunneling Model Without PHB Uniform Model The uniform model makes the LSP an extension of the DiffServ domain of the encapsulated packet. In this model, a packet only has a single meaningful PHB marking (which resides in the most recent encapsulation). LSRs propagate the packet PHB to the exposed encap- sulation when they perform a pop operation. This propagation implies that any packet re-marking is reflected on the packet marking when it leaves the LSP. The LSP becomes an integral part of the DiffServ domain of the packet as opposed to the transparent transport that the pipe and short-pipe models provided. This model proves useful when an MPLS network connects other DiffServ domain and all networks (including the MPLS network) need to behave as a single DiffServ domain. Label Label IP/MPLS LSP Ingress LSP Egress LSP PHB Marking IP or MPLS Packet Tunneled PHB Marking Push Pop Tunneled PHB Marking Defines Packet PHB
MPLS Support for DiffServ 29 Figure 1-13 illustrates the operation of the uniform model with PHP. The LSP ingress encodes the existing packet PHB marking in the pushed encapsulation. When the packet receives the new encapsulation, the encapsulated PHB marking becomes irrelevant. The penultimate hop infers the packet PHB before the pop operation and encodes it in the exposed encapsulation. Figure 1-13 Uniform Tunneling Model with PHP Figure 1-14 shows the details of the uniform model for LSPs without PHP. The operation of the LSP ingress remains the same. The penultimate hop performs a regular label swapping operation. The LSP egress always infers the PHB before the pop operation and propagates the PHB marking to the exposed encapsulation. The uniform model offers the same external behavior regardless of whether the LSP uses PHP. Tables 1-8 and 1-9 summarize the operation of the three tunneling modes with PHP and without PHP, respectively. Label Label IP/MPLS LSP Ingress LSP Egress Penultimate Hop LSP PHB Marking IP or MPLS Packet Push Pop LSP PHB Marking Defines Packet PHB (Propagated Down)
30 Chapter 1: QoS Technology Overview Figure 1-14 Uniform Tunneling Model Without PHP Table 1-8 DiffServ Tunneling Models over MPLS with PHP Model LSP Ingress Penultimate Hop LSP Egress Pipe Not possible. Not possible. Not possible. Short-pipe Preserve tunneled PHB and set PHB in pushed encapsulation. Determine PHB before pop. Determine PHB using forwarding header. Uniform Copy existing packet PHB to pushed encapsulation. Determine PHB before pop and propagate it down. Determine PHB using received header. Table 1-9 Tunneling Models over MPLS Without PHP Model LSP Ingress LSP Egress Pipe Preserve tunneled PHB and set PHB in pushed encapsulation. Determine PHB before pop operations. Short-pipe Preserve tunneled PHB and set PHB in pushed encapsulation. Determine PHB after pop using forwarding header. Uniform Copy existing packet PHB to pushed encapsulation. Determine PHB before pop and propagate it down. Label Label IP/MPLS LSP Ingress LSP Egress LSP PHB Marking IP or MPLS Packet Push Pop LSP PHB Marking Defines Packet PHB (Propagated Down)
Traffic-Management Mechanisms 31 Traffic-Management Mechanisms The implementation of QoS ultimately relies on a collection of traffic-management mechanisms. The evolution of packet switched networks introduced the need for the development of suitable traffic-management mechanisms. These mechanisms help network nodes avoid and manage congestion. Frame Relay and, especially,ATM networks make use of some of these or similar techniques. This section summarizes the key concepts behind traffic management within the context of IP and MPLS networks. These mechanisms represent the building blocks that network nodes use to implement QoS using both the DiffServ and IntServ architectures. Traffic Classification Network nodes generally perform traffic classification before applying traffic-management mechanisms. The aggregate traffic that traverses a node typically combines traffic with different QoS requirements. In those cases, network nodes need to classify the traffic to provide the expected level of differentiation. Traffic classification can be in the form of an MF or BA classifier in the context of DiffServ. Classification can also be in the form of filter specification in IntServ. Traffic classification typically involves stateless inspection of packet headers. In some cases, nodes perform packet payload inspection or even stateful inspection of packets. However, the complexity and processing impact of those two types of classification limits its applicability to particular devices in the network. Traffic Marking Packet marking involves assigning a new value to a QoS-related field in the header of a packet. This marking typically associates the packet with a class or a drop precedence. As discussed earlier, the DiffServ architecture relies on packet marking to indicate the PHB for each packet. Several Layer 2 technologies also make use of packet marking for QoS purposes, as follows: • Ethernet uses a 3-bit priority field in the VLAN header. • ATM uses a 1-bit field to indicate the drop precedence of a cell (cell loss priority or CLP). • Frame Relay uses an equivalent 1-bit field to capture the drop precedence of a frame (Discard Eligible or DE).
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yellow. S. anemonæflòra is of various colours, and very similar to Anemòne. Tritònia, a genus of about twenty-five species. Few of them deserve culture in regard to their beauty. T. crocàta is in our collections, as I. crocàta, which is amongst the finest, and T. zanthospìla has white flowers curiously spotted with yellow. Watsònia, a genus containing several species of showy flowers, several of which are in our collections, under the genus Gladíolus, but the most of the species may easily be distinguished from it by their flat shell formed bulbs. W. iridifòlia is the largest of the genus, and has flowers of a flesh colour. W. ròsea is large growing, the flowers are pink, and on the stem in a pyramid form. W. humilis is a pretty red flowering species. W. fúlgida, once Antholyza fúlgens, has fine bright scarlet flowers. W. rùbens is an esteemed red flowering species, but scarce. These six genera are in general cultivation. There are several of others of merit that our limits will not admit of inserting. We have no doubt there are some splendid species that have not come under our observation, and others which may be obtained from the Cape of Good Hope not known in any collection. Many hundreds of superb bulbs indigenous to that country, and of the same nature and habit of the above, have not been seen in collections. The flowers of those which we have specified are from one to four inches in diameter, ringent, tubular, or campanulate. Pots from four to seven inches diameter, according to the size of the roots, will be large enough. Give them very little water until they begin to grow; then supply moderately, and keep them near the light. Of the Holland or Dutch bulbs, the Hyacinth is the favourite to bloom in the Green-house. A few of the Tulip, Narcissus, Iris, and Crocus, may for variety be also planted with any other that curiosity may dictate. When these are grown in pots, the soil should be four-eighths loam, two-eighths leaf mould, one-eighth decomposed manure, one-eighth sand, well compounded; plant in pots from four to seven inches, keep the crown of the bulb above the surface of the soil, except of the Tulip,
which should be covered two inches. When these roots are potted, plunge them in the garden about three inches under ground; mark out a space sufficient to contain them; throw out the earth about four inches deep, place the pots therein, covering them with earth to the above depth, making it in the form of a bed. Leave a trench all round to carry off the rain. By so doing, the bulbs will root strong, the soil will be kept in a congenial state about them, and they will prove far superior than if done in the common method. Lift them from this bed on the approach of frost, or not later than the second week of December, wash the pots and take them to the Green- house. OF REPOTTING. Vibúrnum. This is a good period to repot all the flowering plants of this genus. For a full description of them, see Green-house, March. The repotting is only intended for young plants that are wanted to grow freely. When the V. tìnus is much encouraged, it does not flower profusely. Lìlium, Lily. There are four species of this splendid genus kept in the Green-house. It has always been our practice to repot them when they begin to grow, though it is said by some that, when removed at that time, they will not flower perfectly. They will not do to be kept above a few weeks out of the ground, and we think they ought never to be kept out any period. We place them here, that a choice may be made by the cultivator of either of the periods, which is not material; observing in either case, that excess of moisture is injurious while they are dormant. L. longiflòrum grows about one foot high, with one or more flowers. L. longiflòrum suavèolens, is sweet-scented, and has only one flower. L. japònicum is the most magnificent, grows about two feet high, with three or more flowers on one stem. L. lancifòlium; we incline to class this with L. speciòsum, there being no apparent distinction in any character. The flowers are all of the purest white. They require from five to seven inch pots.
Flower Garden. SEPTEMBER. OF DAHLIAS. See that all these plants are supported with proper stakes, rods, &c., that the wind may have no effect in breaking down or otherwise destroying the flower stems. Strictly observe their respective heights and colours, that they may be duly disposed and interspersed next year, if not done so this. If the early part of the month is dry, give them liberal supplies of water. GENERAL CARE OF PLANTS IN POTS. All the flowers that are in pots, and intended to be kept in frames during winter, should have a top-dressing, and a general preparation for their winter quarters, by tieing up, &c. The carnation and pink layers that were lifted and potted last month must be brought from the shade as soon as they begin to grow; and those that are not lifted, have them done forthwith, that they may be rooted afresh before the frost sets in. All Wall-flowers and Stocks should be lifted this month, and planted in five to seven inch pots, and treated as directed for carnation layers last month, until they begin to grow, when they must be fully exposed. PREPARE BEDS AND BORDERS FOR BULBOUS ROOTS. Bulbous roots of every character delight in deep free soil; consequently, wherever they are desired to be planted, due attention must be paid to put the soil in proper order, to have them in
perfection. Where there are a quantity intended to be planted, to have them in beds is the general and preferable method. These ought to be dug from eighteen inches to two feet deep, at the bottom of which place three or four inches of decayed manure. Where the soil is poor it should be enriched with well decomposed manure and earth from the woods, incorporating both well with the soil, breaking it all fine. This being done, allow it to stand until the middle of next month, which see for farther directions. GENERAL OBSERVATIONS. Tie up carefully all the Chrysánthemums, Tuberoses, &c. Clear away the stems or haulm of any decayed annuals or herbaceous plants, that nothing unsightly may appear. Be attentive to the collecting of all kinds of seeds.
Rooms. SEPTEMBER. Where there is a quantity of plants to be kept in these apartments, they should be disposed to the best effect, and at the same time in such a manner as will be most effectual to their preservation. A stage of some description is certainly the best, and, of whatever shape or form, it ought to be on castors, that it may, in severe nights of frost, be drawn to the centre of the room. The shape may be either concave, a half circle, or one square side. The bottom step or table should be six inches apart, keeping each successive step one inch farther apart, to the desired height, which may be about six feet. Allowing the first step to be about two feet from the floor, there will be five or six steps, which will hold about fifty pots of a common size. A stage in the form of half a circle will hold more, look the handsomest, and be most convenient. We have seen them circular, and when filled appeared like a pyramid. These do very well, but they must be turned every day, or the plants will not grow regularly. With this attention it is decidedly the best. Green is the most suitable colour to paint them. GENERAL OBSERVATIONS. The directions given for the Green-house this month are equally applicable here. The Tasseled White Chrysanthemum, and a few other late blooming sorts, are particularly adapted for rooms. If there is no convenience to plunge the pots with Dutch bulbs in the garden, as described in the Green-house of this month, give them very little water until they begin to grow.
Hot-House. OCTOBER. Very few directions remain to be given to the department of the Hot-house. The supplies of water for this and the two preceding months are, according to the state and nature of tropical plants, more limited than at any other period of the year. This is the first month of what may be called their dormant state. Observe the herbaceous plants, that they are, as soon as their foliage decays, set aside, in case of being too liberally supplied with water. Airing is highly essential about this period, that the plants may be gradually hardened; but guard against injuring them. The temperature should not be under fifty degrees; when the days are cool, and the wind chilling, airing is not necessary; and when air is admitted, always close up early in the afternoon, whilst the atmosphere is warm, to supersede the necessity of fire as long as possible. If at any time you have recourse to it in this month, use it with great caution. Examine all the shutters and fastenings, and see that they are in good substantial order, and where deficient repair them instantly, that they may be in readiness. Remove all leaves, and give syringings twice a week. Clear off, sweep out, and wash clean, that every part may be in the neatest order.
Green-House. OCTOBER. OF TAKING IN AND ARRANGING THE PLANTS. As observed in the previous month, let the housing of Green- house plants now be attended to. Have all in before the eighth of the month, except a few of the half hardy sorts, which may stand until convenient. Begin by taking in all the tallest first, such as Oranges, Lemons, Myrtles, Oleanders, &c. Limes ought to be kept in the warmest part of the house, otherwise they will throw their foliage. In arrangement, order is necessary to have a good effect; and in small houses it ought to be neat and regular, placing the tallest behind, and according to their size graduating the others down to the lowest in front. Dispose the different sorts in varied order over the house, making the contrast as striking as possible. Having the surface of the whole as even as practicable, with a few of the most conspicuous for shape and beauty protruding above the mass, which will much improve the general appearance, and greatly add to the effect. All succulents should be put together. They will do in a dark part of the house, where other plants would not grow, studying to have the most tender kinds in the warmest part, and giving gentle waterings every three or four weeks. When all are arranged, give them a proper syringing, after which wipe clean all the stages, benches, &c. sweeping out all litter, and wash clean the pavement, which will give to all a neat and becoming appearance. Let the waterings now be done in the mornings, as often and in such quantities as will supply their respective wants, examining the plants every day.
During the continuance of mild weather, the circulation of air must be as free as possible, opening the doors and front and top sashes regularly over the house. But observe in frosty nights, and wet, cloudy weather, to keep all close shut. Be attentive in clearing off decayed leaves and insects. Any plants of Lagerstræmia, Stercùlia, Hydrángea, Pomegranate, and others equally hardy, that are deciduous, may be kept perfectly in a dry, light, airy cellar, giving frequent admissions of air. OF REPOTTING. Anemònes. Where A. nemoròsa flòre plèno and A. thalictròides flòre plèno are kept in pots in the Green-house, they should be turned out of the old earth, and planted in fresh soil. They are both pretty, low growing, double white flowering plants, and require a shaded situation. The latter is now called Thalíctrum anemonoídes. Dáphne, is a genus of diminutive shrubs, mostly evergreens, of great beauty and fragrance. Very few species of them are in our collections. D. odòra, frequently called D. índica, is an esteemed plant for the delightful odour of its flowers, and valuable for the period of its flowering, being from December to March, according to the situation; leaves scattered, oblong, lanceolate, smooth; flowers small, white, in many-flowered terminale heads. D. hybrida is a species in high estimation at present in Europe, but little known here, being only in a few collections; flowers rose-coloured, in terminale heads, and lateral bunches in great profusion, and very similar to the former in habit and shape of flower; blooms from January to May, and is of a peculiar fragrance. D. oleoídes is what may be termed "ever-blooming;" flowers of a lilac colour; leaves elliptic, lanceolate, smooth. D. laurèola, Spurge laurel; D. póntica, D. alpìna, and D. Cneòrum, are all fine species, and in Europe are esteemed ornaments in the shrubbery, but we are not certain if they will prove hardy in our vicinity.
Prímula. There are a few fine species and varieties in this genus, adapted either for the Green-house or Rooms. All the species and varieties will keep perfectly well in a frame, except the China sorts. Having previously observed a few of the other species and varieties, we will observe the treatment of these. P. sinénsis, now prænitens, known commonly as China Primrose; flowers pink, and in large proliferous umbels, flowering almost through the whole year, but most profusely from January to May. Keep them in the shade, and be careful that they are not over-watered during summer. As the stems of the plant become naked, at this repotting a few inches should be taken off the bottom of the ball, and placing them in a larger pot will allow the stems to be covered up to the leaves. P. p. albiflòra, colour pure white and beautiful. P. p. dentiflòra. There is also a white variety of this, both similar to the two former, only the flower indented. All these require the same treatment. As they only live a few years, many individuals, to propagate them, divide the stems, which in most cases will utterly destroy them. The best, and we may say the only method to increase them, is from seed, which they produce in abundance every year. Pæonia, is a magnificent genus. There are four varieties of them, half hardy and half shrubby. They will bear the winter if well protected, but are better in the Green-house. These are P. moután, Tree Pæony; the flower is about four inches in diameter, of a blush colour, and semi-double; P. M. Bànksii is the common Tree Pæony, and called in our collection P. Moutàn; it has a very large double blush flower, and is much admired. P. M. papaveràcea is a most magnificent variety; has large double white flowers, with pink centres; P. M. ròsea is a splendid rose-coloured double variety, and is scarce. These plants ought not to be exposed to the sun while in flower, as the colours become degenerated, and premature decay follows. If the Dutch bulbs intended for flowering during winter are not potted, have them all done as soon as possible, according to directions given last month.
CAMELLIAS. These plants ought to have a thorough examination, and those that were omitted in repotting before they commenced growing, may be done in the early part of this month; but it is not adviseable, except the roots are matted round the ball of earth, which should be turned out entire. Examine all the pots, stir up the surface of the earth, and take it out to the roots, supplying its place with fresh soil. Destroy any worms that may be in the pots, as they are very destructive to the fibres. Look over the foliage and with a sponge and water clear it of all dust, &c. Frequently the buds are too crowded on these plants, especially the Double white and Variegated. In such case pick off the weakest, and where there are two together, be careful in cutting, so that the remaining bud may not be injured. This is the best period of the year to make selections of these, as they now can be transported hundreds of miles without any material injury, if they are judiciously packed in close boxes. In making a choice of these, keep in view to have distinctly marked varieties, including a few of those that are esteemed as stocks for producing new kinds, which are undoubtedly indispensable; and will reward the cultivator in a few years with new sorts. Besides, it will afford unbounded gratification to behold any of these universally admired ornaments of the Green-house improving by our assistance and under our immediate observation. There is nothing to prevent any individual from producing splendid varieties in a few years. Mr. Hogg correctly observes, "It is very probable in a few years we shall have as great a variety of Camellias, as there are of Tulips, Hyacinths, Carnations, Auriculas, &c." It has been often said that these plants are difficult of cultivation. This is unfounded, indeed they are the reverse if put in a soil congenial to their nature. When highly manured soils are given, which are poisonous to the plants, sickness or death will inevitably ensue; but this cannot be attributed to the delicacy of their nature. We can unhesitatingly say there is no Green-house plant more hardy
or easier of cultivation, and they are equally so in the parlour, if not kept confined in a room where there is a continuance of drying fire heat, their constitution not agreeing with an arid atmosphere.
Flower-Garden. OCTOBER. OF PLANTING VARIOUS BULBOUS FLOWER ROOTS. From the middle of October to the beginning of November is the best period for a general planting of Dutch bulbs. Cròcuses are the earliest in flower, and may be planted about six inches off the edgings, about four inches apart and two deep, or in beds four feet wide; the varieties selected and planted across the bed in rows of distinct colours, they flowering so early, and in that manner have a grand effect. There are above sixty varieties to be had. Hyacinths. The ground that was prepared for these last month, should be all divided into beds four feet wide, leaving between each alleys of twenty inches. Skim off three inches of the surface of the former into the latter, level the bed smoothly with the rake, and mark it off in rows eight inches apart. Plant the roots in the row eight inches asunder. Thus they will be squares of eight inches, and by planting the different colours alternately the bed will be beautifully diversified. Press each root gently down with the hand, that in covering up they may not be displaced. Put about four inches of earth over the crowns, which will make the beds from two to three inches higher than the alleys. The beds before and after planting should be gently rounded from the middle to each side to let the rain pass off. Finish all by raking evenly, straighten the edgings with the line, and clear out the alleys or pathways. Tulips like a lighter and richer earth than Hyacinths. Prepare the beds in the same manner, and so as the roots will stand nine inches
apart each way; cover them five inches deep, as the new bulbs are produced above the old. If it is intended to screen either of these while in flower, the beds should be made wider. Where two beds are to be shaded under one awning, make the alleys alternately two or three feet wide; the one two feet wide to be under the awning. Polyanthus and Italian Narcissus, may be planted in every respect as Hyacinths, only they require a lighter and richer soil. Jonquils. Plant these in the same soil as Tulips, six inches apart, and cover three inches deep. They do not flower so well the first year as in the second and third, therefore should only be lifted every third year. Anemones and Ranunculuses. These roots like a fresh rich, well pulverized, loamy soil. In light sandy soils they will languish in early droughts, and sometimes do not show their flowers fully. Cow manure is the best to use for enriching the soil. The whole should be well mixed and incorporated to the depth of eighteen or twenty inches. The roots may be planted in four-foot beds, or in such a manner as a low frame of boards can be placed over them, when the winter sets in very severe. If intended to be shaded while in flower, leave a sufficiency of space in the alleys as directed for Tulips and Hyacinths. Do not raise the beds above one inch higher than the alleys, and form the surface level, in order to detain rather than throw off moisture. Then draw drills exactly two inches deep and six inches apart across the bed. In these place the roots, claws down, about four inches distant from each other. The roots of the Anemones are flat, and the side on which there are small protuberances, is that from which the stems proceed. Press each root a little down with the hand, and cover all carefully so as not to displace them. Smooth the surface with the rake, leaving the bed quite level. Many other bulbous flowers might be added to the above; but as their culture is so similar, it would be superfluous to say more of
them. They should be allowed space and depth according to the size of the bulb; a covering of two inches for the smallest, and five for the largest, will generally answer, and the intermediate roots in proportion. We will enumerate a few of the different kinds, Starch and Musk Hyacinths; of Narcissus, the Paper, Grand Monarque, and Nodding, with the two previously mentioned, are the most profuse in flower. Some of them will have above twelve flowers on one stem. Of Lilies, all the varieties of Mártagon, Tigrìnum and Chalcedónicum, with our native species and varieties. Of Iris, Lusitánica, two varieties, yellow and blue; Xiphioídes, or Ziphioídes; and Pérsica, are the finest of the bulbous sorts. Snow-drop with several other minor bulbs. All of these flowering bulbs may be advantageously planted in patches through the garden by taking out about one square foot of earth. Break it well, and if poor enrich it. Plant four bulbs in each of the same colour, and the clumps that are contiguous to contain different colours. PLANTING AND TRANSPLANTING. This is a very proper period to plant the beautiful and early flowering Pyrus japónica, now called Cydónia japónica. The blossoms are of a rich scarlet colour. It is the earliest flowering shrub of the garden, and deciduous, though said by some to be "an evergreen." The plant is bushy, and well adapted for single plants in grass plats, or forming low ornamental hedges. There is likewise C. j. álba, a fine white variety of the same habit, and both are of the hardiest nature —also for the various species of Anemònes and all the herbaceous Pæonias. Of the latter there are above nineteen species and twenty-two varieties, a few of which are particularly esteemed, and exceedingly handsome. P. èdulis whitlíji is a splendid large double P èdulis white; P. Hùmei is a beautiful large double dark blush; P. èdulis fràgrans is a fine large double scarlet, rose-scented variety. These three plants
ought to be in every garden. The flowers are full in the centre, and frequently above six inches in diameter; P. álba chinènsis is said to be the largest and finest of the herbaceous sorts; colour pure white, with pink at the bottom of the petals—it is a scarce variety; P. paradóxa fimbàtria, fringed double red, and esteemed; P. officinális rúbra is the common double red. There are several other very fine single species and varieties, the flowers of which are principally red or blush, but none so magnificent as the above mentioned. This is perhaps a more favourable period to plant Dodecátheon than March; for its character see that month of this department. Asclèpias tuberòsa should now be planted. Double Primroses, Polyanthus, Daisies, &c. Any of these that were planted in shaded situations in spring, and have been preserved through the summer, should have for their farther protection a bed well sheltered from the north west, in which they should be planted four inches apart. Give them a few sprinklings of water in the morning, and have a temporary frame of rough boards put together to place over them during the severity of winter. The frame may be covered with the same in place of glass, which must be kept over them while they are in a frozen state. Any other plants that are in the ground, which are intended to be protected with frames through the winter, ought to be immediately lifted and potted; and treated as directed for all new potted plants. GRASS AND GRAVEL WALKS. The former should be trimly cut and well rolled this month, that they may appear neat all winter. Never allow decayed leaves to lay any time upon them, as they are apt to rot out the grass. The latter should be divested of every weed, and receive a firm rolling. Clear them at all times of leaves and other litter. These, if on a declivity, and have not a firm substantial bottom, will be subject to be cut up with every heavy rain. A break should be put in every twenty, forty,
or eighty feet, to throw off the water. A strong plank will answer perfectly well, but in such situations we would prefer grass-walks. PLANTING EVERGREENS. This month is the best period in autumn to plant these shrubs, and where there is a great extent to be planted it would be advisable to do a part of it now; but we give the preference to April, which see for directions. GENERAL OBSERVATIONS. When the plantings of bulbs, &c. are finished, every part of the garden should have a thorough cleaning. All annual flowers will have passed the season of their beauty; therefore, remove the decayed flower stems or haulm, and trim off the borders. Dig all vacant ground, especially that intended to be planted with shrubs in the ensuing spring, which ought to be dug from one to two feet deep. Roses delight in a deep light soil.
Rooms. OCTOBER. Have a stage or stages, as described last month, in the situations where they are intended to remain all winter; place the plants on them from the first to the eighth of this month, beginning with the tallest on the top, graduating to the bottom. It is desirable to place flats or saucers under each, to prevent the water from falling to the floor, and the water should be emptied from the flats of all except those of Cálla and Hydrángea. The latter while dormant should be kept only a little moist. Previous to taking in the plants, they should be divested of every decayed leaf, insects, and all contracted dust, having their shoots neatly tied up, and every one in correct order. Every leaf of the Caméllias ought to be sponged, and the plants placed in a cool airy exposure, shaded from the direct rays of the sun. If the flower buds are too crowded, picking off the weakest will preserve the remainder in greater perfection, and prevent them in part from falling off. Do not on any occasion keep them in a room where there is much fire heat, as the flower buds will not expand in an arid atmosphere. See Green-house this month more largely on this subject. OF BULBOUS ROOTS. Those that are intended to flower in glasses, should be placed therein this month and kept in a cool room. After the fibres begin to push a few shoots, the glasses may be taken to the warmest apartments to cause them to flower early. Bring a few from the coldest to the warmest every two weeks, and thus a succession of bloom may be kept up from January to March. Where the roots
intended for pots are still out of the ground, the sooner they are planted the better. (See last month for directions.) Cape Bulbs. All that are unplanted and offering to grow, should be put in pots forthwith. Ample directions are given for the planting of these in the two preceding months. Repot Rùbus rosæfòlius, or Bramble-rose. They should have pots one size larger than those they are now in. To make them flower profusely, when done blooming in May, divide them and put only a few stems in one pot, and repot them in this month, as above directed. GENERAL OBSERVATIONS. Any herbaceous plants in the collection ought to be set aside, and the water in part withheld. When the stems and foliage are decayed, the plants may be put in a cool cellar, where they will not be in danger of frost, and be permitted to remain there until they begin to grow; then bring them to the light, and treat as directed for these kinds of plants. Deciduous plants may be treated in a similar manner.
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Qos For Ipmpls Networks Gallo Mark Zhang Raymond Alvarez Santiago

  • 1.
    Qos For IpmplsNetworks Gallo Mark Zhang Raymond Alvarez Santiago download https://ebookbell.com/product/qos-for-ipmpls-networks-gallo-mark- zhang-raymond-alvarez-santiago-22009004 Explore and download more ebooks at ebookbell.com
  • 3.
    800 East 96thStreet Indianapolis, IN 46240 USA Cisco Press QoS for IP/MPLS Networks Santiago Alvarez
  • 4.
    ii QoS for IP/MPLSNetworks Santiago Alvarez Copyright© 2006 Cisco Systems, Inc. Published by: Cisco Press 800 East 96th Street Indianapolis, IN 46240 USA All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage and retrieval system, without writ- ten permission from the publisher, except for the inclusion of brief quotations in a review. Printed in the United States of America 1 2 3 4 5 6 7 8 9 0 First Printing June 2006 Library of Congress Cataloging-in-Publication Number: 2004117089 ISBN: 1-58705-233-4 Trademark Acknowledgments All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capital- ized. Cisco Press or Cisco Systems, Inc. cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of any trademark or service mark. Warning and Disclaimer This book is designed to provide information about quality of service in IP/MPLS networks using Cisco IOS and Cisco IOS XR. Every effort has been made to make this book as complete and as accurate as possible, but no war- ranty or fitness is implied. The information is provided on an “as is” basis. The authors, Cisco Press, and Cisco Systems, Inc. shall have neither liability nor responsibility to any person or entity with respect to any loss or damages arising from the information contained in this book or from the use of the discs or programs that may accompany it. The opinions expressed in this book belong to the author and are not necessarily those of Cisco Systems, Inc. Corporate and Government Sales Cisco Press offers excellent discounts on this book when ordered in quantity for bulk purchases or special sales. For more information please contact: U.S. Corporate and Government Sales 1-800-382-3419 corpsales@pearsontechgroup.com For sales outside the U.S. please contact: International Sales international@pearsoned.com Feedback Information At Cisco Press, our goal is to create in-depth technical books of the highest quality and value. Each book is crafted with care and precision, undergoing rigorous development that involves the unique expertise of members from the professional technical community.
  • 5.
    iii Readers’ feedback isa natural continuation of this process. If you have any comments regarding how we could improve the quality of this book, or otherwise alter it to better suit your needs, you can contact us through e-mail at feedback@ciscopress.com. Please make sure to include the book title and ISBN in your message. We greatly appreciate your assistance. Publisher Paul Boger Cisco Representative Anthony Wolfenden Cisco Press Program Manager Jeff Brady Production Manager Patrick Kanouse Development Editor Jill Batistick Senior Project Editor San Dee Phillips Copy Editor Keith Cline Technical Editors Mark Gallo, Raymond Zhang Book and Cover Designer Louisa Adair Composition Mark Shirar Indexer Keith Cline
  • 6.
    iv About the Author SantiagoAlvarez, CCIE No. 3621, is a technical marketing engineering for Cisco Systems working on MPLS and QoS since 2000. He joined Cisco in the blazing days of 1997. Prior to Cisco, Santiago worked in software development for Lucent Technologies. He has been involved with computer net- working since 1991. Santiago is a frequent speaker at Cisco Networkers and a periodic contributor to Cisco Packet Magazine. He holds a bachelor of science degree in computer science from EAFIT Uni- versity, a master of Science degree in computer science from Colorado State University, and a master of science in telecommunications from the University of Colorado at Boulder. Outside work, he enjoys the outdoors, fine food, and exploring the world as an independent traveler. He can be reached at saalvare@cisco.com.
  • 7.
    v About the TechnicalReviewers Mark Gallo is a systems engineering manager at Cisco Systems within the channels organization. He has led several engineering groups responsible for positioning and delivering Cisco end-to-end systems, as well as designing and implementing enterprise LANs and international IP networks. He has a B.S. degree in electrical engineering from the University of Pittsburgh and holds Cisco CCNP and CCDP certifications. Mark resides in northern Virginia with his wife, Betsy, and son, Paul. Raymond Zhang is a senior network architect for BT Infonet in the areas of Global IP backbone infra- structure, routing architecture design, planning, and its evolutions. Currently, his main areas of interest include large-scale backbone routing, traffic engineering, performance and traffic statistical analysis, and MPLS-related technologies (including interdomain traffic engineering, GMPLS, metro Ethernet, Diffserve, IPv6, and Multicast). Raymond participates in several IETF drafts relating to MPLS, BGP- based MPLS VPN, Inter-AS TE, and, more recently, PCE-based work.
  • 8.
    vi Dedications Thanks for withstandinglong, long working hours.
  • 9.
    vii Acknowledgments I would liketo give special thanks to Bob Olsen and Sandeep Bajaj for sharing their technical expertise through so many years. They have patiently tolerated my constant interruptions and have provided use- ful insight on different topics included in the book. Special thanks to the reviewers, Mark Gallo and Raymond Zhang. I appreciate your detailed comments. I am to blame for any remaining inaccuracies or omissions. Big thanks to Bruce Davie, whose responsiveness at key points encouraged me to persist in my goal. I highly regard his unusual ability to abstract complexity and clearly illustrate the essence of intricate technology concepts. Much of his work has directly and indirectly influenced the content of this book. Similarly, I extend my gratitude to François Le Faucheur and Jean Philippe Vasseur. They have had the patience to discuss with me many aspects of these technologies in numerous occasions. Merci! Thanks to Ramesh Uppili for contributing to the presentation of key topics in multiple ways. I also want to thank Rakesh Gandi, Prashanth Yelandur, Ashish Savla, Bobby Kaligotla, Lawrence Wobker, Ashok Ganesan, Jay Thontakudi, and ScottYow for facilitating the discussion of Cisco IOS XR in this book. Special thanks to the Cisco Press team: John Kane, Chris Cleveland, Jill Batistick, San Dee Phillips, and Elizabeth Peterson. I really appreciate your attention to detail and extraordinary patience with me. I wish John the best in his new endeavors. Finally, if you have read this far in search of your name, this paragraph is for you. I have to acknowledge that numerous individuals contributed through insightful discussions. They unhappily or maybe happily remain anonymous. Thanks!
  • 10.
    viii This Book IsSafari Enabled The Safari® Enabled icon on the cover of your favorite technology book means the book is available through Safari Bookshelf. When you buy this book, you get free access to the online edition for 45 days. Safari Bookshelf is an electronic reference library that lets you easily search thousands of technical books, find code samples, download chapters, and access technical information whenever and wherever you need it. To gain 45-day Safari Enabled access to this book: • Go to http://www.ciscopress.com/safarienabled • Complete the brief registration form • Enter the coupon code 2ML4-YT1N-YR8J-D5NQ-DAH4 If you have difficulty registering on Safari Bookshelf or accessing the online edition, please e-mail customer-service@safaribooksonline.com.
  • 11.
    ix Contents at aGlance Foreword xv Introduction xvii Chapter 1 QoS Technology Overview 3 Chapter 2 MPLS TE Technology Overview 57 Chapter 3 Cisco QoS 79 Chapter 4 Cisco MPLS Traffic Engineering 143 Chapter 5 Backbone Infrastructure 201 Appendix A Command Reference for Cisco MPLS Traffic Engineering and RSVP 265 Index 282
  • 12.
    x Contents Foreword xv Introduction xvii Chapter1 QoS Technology Overview 3 IP QoS Architectures 3 Integrated Services 4 IntServ Terminology 5 Architecture Principles 5 Service Model 6 Use of RSVP in IntServ 8 Differentiated Services 9 DiffServ Terminology 9 Architecture Principles 10 Differentiated Services Code Point 11 Nodes, Domains, and Regions 13 Traffic Classification and Conditioning 13 Per-Hop Behaviors 15 MPLS Support for IntServ 18 MPLS Support for DiffServ 19 E-LSP 20 L-LSP 22 DiffServ Tunneling Models over MPLS 25 Pipe Model 25 Short-Pipe Model 26 Uniform Model 28 Traffic-Management Mechanisms 31 Traffic Classification 31 Traffic Marking 31 Traffic Policing 32 Traffic Shaping 35 Congestion Management 37 Active Queue Management 40 Link Fragmentation and Interleaving 42 Header Compression 44 QoS Signaling 45 Resource Reservation Protocol 45 Design Principles 46 Protocol Messages 47 Protocol Operation 49 Other QoS Signaling Mechanisms 51
  • 13.
    xi Summary 52 References 52 Chapter2 MPLS TE Technology Overview 57 MPLS TE Introduction 57 Basic Operation of MPLS TE 59 Link Information Distribution 59 Path Computation 60 TE LSP Signaling 63 Traffic Selection 64 DiffServ-Aware Traffic Engineering 64 Class-Types and TE-Classes 66 Bandwidth Constraints 68 Maximum Allocation Model 68 Russian Dolls Model 70 Fast Reroute 71 Link Protection 74 Node Protection 74 Summary 76 References 77 Chapter 3 Cisco QoS 79 Cisco QoS Behavioral Model 79 Classification Component 80 Pre-Queuing Component 80 Queuing Component 81 Enqueuing Subcomponent 81 Dequeuing Subcomponent 82 Post-Queuing Component 84 Modular QoS Command-Line Interface 84 Hardware Support for the MQC 87 Traffic-Management Mechanisms 87 Traffic Classification 88 Traffic Marking 94 Traffic Policing 100 Traffic Shaping 108 Congestion Management 115 Active Queue Management 121 Link Fragmentation and Interleaving 127 Header Compression 128 Hierarchical Configurations 129 Hierarchical Classification 129
  • 14.
    xii Hierarchical Policies 130 Percentage-BasedRates 132 Parameter Units 133 Processing of Local Traffic 135 Summary 139 References 140 Chapter 4 Cisco MPLS Traffic Engineering 143 Basic Operation of MPLS TE 143 Enabling MPLS TE 144 Enabling MPLS TE on a Node 144 Enabling MPLS TE on an Interface 145 Defining a TE Tunnel Interface 146 Link Information Distribution 148 Using IS-IS for Link Information Distribution 148 Using OSPF for Link Information Distribution 149 Controlling Flooding 150 Configuring Link Attributes 150 Verifying Link Information Distribution 153 Path Computation 156 Configuring the TE LSP Path 156 Configuring the TE LSP Constraints 157 Path Reoptimization 159 Verifying Path Computation 160 Signaling of TE LSPs 163 Configuring RSVP 163 Verifying RSVP 164 Verifying Signaling of TE LSPs 167 Traffic Selection 172 Traffic-Selection Alternatives 172 Class-Based Tunnel Selection 173 DiffServ-Aware Traffic Engineering (DS-TE) 175 Prestandard DS-TE 175 Class-Types and TE-Class 176 Defining a DS-TE Tunnel Interface 177 Configuring Bandwidth Constraints 179 Verifying DS-TE Link Information Distribution 181 Verifying Signaling of DS-TE LSPs 182 Fast Reroute (FRR) 182 Link and Node Protection 183 Bandwidth Protection 187
  • 15.
    xiii Verifying FRR onthe Headend 191 Verifying FRR on the PLR 193 Summary 198 References 198 Chapter 5 Backbone Infrastructure 201 Backbone Performance 201 Performance Requirements for Different Applications 202 Segmentation of Performance Targets 204 Factors Affecting Performance Targets 206 Latency Versus Link Utilization 207 Reference Network 210 Edge Nodes 210 QoS Design Alternatives 212 Best-Effort Backbone 213 Best-Effort Backbone with MPLS TE 219 DiffServ Backbone 226 DiffServ Backbone with MPLS TE 233 DiffServ Backbone with DiffServ-Aware Traffic Engineering 240 Adding MPLS TE FRR 251 What Design Should I Use? 260 Summary 261 References 261 Appendix A Command Reference for Cisco MPLS Traffic Engineering and RSVP 265 Index 282
  • 16.
    xiv Icons Used inThis Book Command Syntax Conventions The conventions used to present command syntax in this book are the same conventions used in the IOS Command Reference. The Command Reference describes these conventions as follows: • Boldface indicates commands and keywords that are entered literally as shown. In actual configuration examples and output (not general command syntax), boldface indicates commands that are manually input by the user (such as a show command). • Italics indicate arguments for which you supply actual values. • Vertical bars (|) separate alternative, mutually exclusive elements. Note, however, that the vertical bar (pipe operand) is also used to filter command-line interface command output; in that scenario, the operand (|) precedes the begin, exclude, or include keywords, which are then followed by a regular expression. • Square brackets [ ] indicate optional elements. • Braces { } indicate a required choice. • Braces within brackets [{ }] indicate a required choice within an optional element. PC PC with Software Sun Workstation Macintosh Terminal File Server Web Server Cisco Works Workstation Printer Laptop IBM Mainframe Front End Processor Cluster Controller Modem DSU/CSU Router Bridge Hub DSU/CSU Catalyst Switch Multilayer Switch ATM Switch ISDN/Frame Relay Switch Communication Server Gateway Access Server Network Cloud Token Ring Token Ring Line: Ethernet FDDI FDDI Line: Serial Line: Switched Serial
  • 17.
    xv Foreword The phrase “IPQoS” was for many years considered an oxymoron. Indeed, much of the success of the IP architecture could be traced to its adoption of a "best effort" service model, enabling IP to run over just about any underlying network technology. Best effort service, however, is defined by a lack of assurance that packets will be delivered in a timely manner, or even delivered at all. Such a service model limits the potential of IP networks to support applications that demand timely packet delivery, such as interactive telephony and multimedia applications. As far back as 1979, there were proposals to extend the IP service model to support applications with stronger QoS requirements. However, this remained a research topic until the early 1990s. By that point, the idea of convergence—carrying many applications with diverse QoS needs on a single network—was gaining currency, although the word “convergence” would not become a buzzword for several years. ATM was widely expected to be the packet switching technology that would enable this convergence, but a concerted effort to add QoS to IP was also getting underway. The seminal 1992 paper by Clark, Shenker, and Zhang on support of real-time applications in the Internet put a serious stake in the ground for IP QoS, and work at the IETF to standardize a set of IP QoS mechanisms began shortly thereafter. The Integrated Services architecture and Resource Reservation Protocol resulted, and the Differentiated Services architecture followed. Another technical development with big implications for IP QoS was Multiprotocol Label Switching, which grew out of work on Tag Switching at Cisco begun in 1996. There was considerable confusion about exactly what impact MPLS would have on IP QoS, in part because of the resemblances between MPLS and ATM, which had its own QoS model. In reality, the biggest single effect MPLS had on QoS was to add another tool to the QoS toolbox, in the form of traffic engineering with constraint-based rout- ing. It is for this reason more than any other that MPLS and QoS deserve to be covered in a single book. Which brings us to the current volume. IP QoS can now be considered a mature technology, not just something for the bleeding edge. It is also notoriously complex to understand and to configure cor- rectly. Some of this complexity is intrinsic; some is an accident of history. On the intrinsic side, under- standing QoS is hard because it requires the ability to operate at many different levels of abstraction. One needs to understand the high level QoS architectures, to have a behavioral model of QoS features inside a router, to know how those features map onto a particular piece of hardware, and to understand the CLI that is used to control those features. This is where this book sets itself apart from the pack of QoS books. Some cover QoS architecture and IETF standards. Some provide information on CLI com- mands. But this is the only book I've found that walks the reader through the levels of abstraction from high level architecture to low level CLI, with a clear explanation of the abstract QoS behavior model that all routers support providing the bridge between the levels. By reading this book, you will under- stand both the big picture of QoS and the details necessary to deploy it in a real network. Another factor that made QoS difficult to manage in the past was a somewhat ad hoc approach to its implementation. Combinations of features were sometimes implemented in a monolithic way, and inconsistency across platforms was the norm. This situation has improved massively in recent years, notably with the adoption of the Modular QoS CLI across most of the Cisco product line. Thus, QoS deployment is much more straightfoward than it once was, and this book's timely coverage of the MQC and its underlying behavioral model will make it even easier.
  • 18.
    xvi Many readers maybe tempted to jump straight to the last chapter's guidance on how to design and deploy a QoS strategy in a backbone network. Santiago's extensive real-world deployment experience certainly makes this chapter especially valuable. However, the preceding four chapters are the ones that will provide you with a fundamental understanding of QoS. Thus, rather than blindly following a QoS "recipe," you'll be able to make the right design decisions to meet the needs of your own applications and customers. If you really want to understand QoS fully, this is the book to read, from start to finish. Bruce Davie Cisco Fellow .
  • 19.
    xvii Introduction The motivation behindthis book is the continued interest in the implementation of quality of service (QoS) in IP/MPLS networks. QoS arises as a key requirement for these networks, which have become the preferred technology platform for building converged networks that support multiple services. The topic can be one of the most complex aspects of the network design, implementation, and operation. Despite the importance of and interest in this topic, no other Cisco Press title provides a detailed discus- sion of this subject. A significant amount of the content of this book also applies to pure IP networks that do not have immediate plans to migrate to a full IP/MPLS network. This material covers both QoS and Multiprotocol Label Switching Traffic Engineering (MPLS TE). In particular, it covers MPLS TE as a technology that complements traditional QoS technologies. MPLS TE can be an instrumental tool to improve the QoS guarantees that an IP/MPLS network offers. As such, it can contribute to improving both network performance and availability. However, this book pro- vides a concise discussion of MPLS TE. Those readers interested in further information should consult the Cisco Press title Traffic Engineering with MPLS. The book takes the point of view of those individuals responsible for the IP/MPLS network. Other Cisco Press titles describe the details of the QoS implementation for those devices receiving the services that the network offers. You should have a basic understanding of both IP and MPLS to obtain the most benefit from this book. That understanding should include basic IP addressing and routing, along with the basics of MPLS for- warding. However, the book provides a technology overview of QoS and MPLS TE to help those with less exposure to these technologies or to serve as a review/reference to those more familiar with those topics. This book touches a broad topic and does not pretend to address all QoS aspects of interest. You can expect future Cisco Press books to cover important areas, including the following: • Implementation of QoS for specific services (for instance, IP, Ethernet, ATM) • QoS management (including monitoring and provisioning) • Interprovider QoS Visit this book’s website, http://www.ciscopress.com/title/1587052334, for further information.
  • 20.
    xviii Who Should ReadThis Book? This book’s primary audience is the technical staff of those organizations building IP/MPLS networks as an infrastructure to provide multiple services. The material includes technology, configuration, and operational details to help in the design, implementation, and operation of QoS in IP/MPLS networks. Service providers are a prime example of the organizations that this book targets. However, government agencies, educational institutions, and large enterprises pursuing IP/MPLS will find the material equally useful. A secondary audience for this book is those individuals in charge of service definition or those individu- als subscribing to network services. Both types can benefit from a better understanding of the differenti- ation capabilities that IP/MPLS networks can offer. How This Book Is Organized Although this book could be read cover to cover, it is designed to be flexible and allow you to easily move between chapters and sections of chapters to cover just the material that you need more work with. The content is roughly divided into three parts: • Chapters 1 and 2 provide a technology overview. • Chapters 3 and 4 discuss Cisco implemenation. • Chapter 5 covers different backbone design options. Here is a brief synopsis of each chapter: Chapter 1, “QoS Technology Overview”—This chapter provides a review of QoS technology for IP and IP/MPLS networks. The chapter initially discusses the IP QoS architectures and how they apply to MPLS. Multiple sections elaborate on MPLS support for Differentiated Services (DiffServ), including a detailed discussion on EXP-inferred-class link switched path (E-LSP), Label-inferred-class LSP (L- LSP), and DiffServ tunneling models (pipe, short pipe, and uniform). This dicussion leads into a sum- mary of traffic-management mechanisms with a detailed look at traffic policing, traffic shaping, traffic scheduling, active queue manangemt, and so on. The chapter also discusses QoS signaling with a focus on the Resource Reservation Protocol (RSVP). Chapter 2, “MPLS TE Technology Overview”—This chapter reviews the basic operation of this tech- nology with its DiffServ extensions and applicability as a traffic-protection alternative. This review elaborates on the concepts of contraint-based routing, DiffServ-aware Traffic Engineering (DS-TE) and fast reroute (FRR) (including link, shared-risk link group, and node protection). Chapter 3, “Cisco QoS”—This chapter covers the Cisco QoS behavioral model and the modular QoS command-line interface (MCQ). The chapter abstracts the platform specifics to facilitate the under- standing of Cisco QoS and provides a complete reference of the configuration commands. In addition, the chapter includes numerous examples to illustrate the configuration and verification of different traf- fic-management mechanisms in Cisco IOS and Cisco IOS XR. This material is equially relevant to IP and IP/MPLS networks.
  • 21.
    xix Chapter 4, “CiscoMPLS Traffic Engineering”—This chapter presents Cisco implementation of MPLS Traffic Engineering in both Cisco IOS and Cisco IOS XR. It includes multiple configuration and verification examples illustrating the implementation of basic MPLS TE, DS-TE, and FRR. Chapter 5, “Backbone Infrastructure”—This chapter discusses the backbone performance require- ments and the different design options. The chapter reviews different designs, ranging from a best-effort backbone to the most elaborate scenarios combining DiffServ, DS-TE, and FRR. Numerous configura- tion examples illustrate their implementation using Cisco IOS and Cisco IOS XR.
  • 23.
    C H AP T E R 1 QoS Technology Overview In this chapter, you review the following topics: • IP QoS Architectures • MPLS Support for IntServ • MPLS Support for DiffServ • Traffic-Management Mechanisms • QoS Signaling This chapter provides a review of the key technology components of quality of service (QoS) in IP/MPLS networks. This review discusses the IntServ and DiffServ architectures including their relationship with MPLS. The chapter covers the traffic management mechanisms that enable QoS implementation and reviews different QoS signaling alternatives in IP/MPLS with a special focus on RSVP protocol. This book assumes that you are already familiar with the basic concepts behind these topics. You should also be familiar with the basics of Multiprotocol Label Switching (MPLS) in general. This chapter and Chapter 2, “MPLS TE Technology Overview,” serve as a technology review and quick reference for later content. Chapter 3, “Cisco QoS,” covers the specifics on Cisco implementation of QoS technology. The “References” section at the end of this chapter lists sources of additional information on the topics that this chapter covers. IP QoS Architectures Originally, IP was specified a best-effort protocol. One of the implications of this service definition was that the network would attempt to deliver the traffic to its destination in the shortest time possible. However, the network would provide no guarantee of achieving it. This service definition proved successful during the early Internet years, when data applications constituted the bulk of Internet traffic. Generally, these applications used TCP and therefore adapted gracefully to variations in bandwidth, latency, jitter, and loss. The amount of interactive traffic was minimal, and other applications requiring stricter guarantees were at an experimental stage.
  • 24.
    4 Chapter 1:QoS Technology Overview However, a new generation of applications with new service requirements emerged as the Internet grew in success. The increasing reach and capacity of the Internet made it an attractive infrastructure to support an increasing number of applications. In addition, corporations, governments, and educational institutions, among others, found the IP protocol an appealing option to build their private data networks. Many of the new IP applications (for example, voice and video) had a real-time nature and limited tolerance to variations in bandwidth, latency, jitter, and loss. The service expectations of network users and their application requirements made the best-effort service definition insufficient. The definition of a QoS architecture started in the middle of the 1990s. Since then, the Internet Engineering Task Force (IETF) has defined two QoS architectures for IP: Integrated Services (IntServ) and Differentiated Services (DiffServ). The IntServ architecture was the initial proposed solution. Subsequently, the DiffServ architecture came to life. MPLS later incorporated support for the DiffServ architecture, which the IETF had defined exclusively for IP. These two architectures use different assumptions and take different approaches to bringing QoS to IP.Although sometimes considered opposite and competing architectures, they tend to complement each other. Moreover, the QoS mechanisms used ultimately to manipulate traffic are essentially the same in both architectures. Integrated Services The IntServ working group was responsible for developing the specifications of this architecture at the IETF. The group met for the first time during the twenty-ninth IETF in 1994. The architecture specifications have a close relationship with the work of the IntServ over Specific Link Layers (ISSLL) and the Resource Reservation Protocol (RSVP) working groups. The ISSLL working group defined the implementation of IntServ over different link-layer protocols (for example, Ethernet and ATM). The RSVP working group defined the RSVP protocol that the IntServ group selected as the signaling protocol. The three working groups collectively produced 32 RFCs, of which 24 are in the IETF standards track. The working groups eventually closed between the years 2000 and 2002. The IETF decided to modify the original Internet architecture to support real-time applications. The IETF considered simpler alternatives, but they offered less-complete solutions. For instance • Fair-queuing algorithms solved the unfairness between data and real-time applications, but they could not guarantee the delay and jitter. • The use of separate networks for separate services was less efficient due to the lower levels of statistical multiplexing. • Bandwidth overprovisioning was not a realistic solution when bandwidth was offered as a service.
  • 25.
    IP QoS Architectures5 • A simple priority mechanism could not prevent a growing number of real-time flows from causing degradation of all flows. • The rate and delay adaptation of real-time applications had limits, especially when no admission control was used. IntServ Terminology This section lists several important terms that IntServ introduces. The next two sections provide more detail about these abstractions: • Flow—An identifiable stream of packets that a network node associates with the same request for QoS. A flow may span a single or multiple application sessions. • Traffic specification (TSpec)—Characterization of the traffic pattern of a flow over time. • Service request specification (RSpec)—Characterization of the QoS a flow desires. • Flow specification (flowspec)—Combination of a TSpec and an RSpec. Network nodes use the flowspec as input for admission-control decisions. Architecture Principles A crucial principle of the IntServ architecture is the requirement for resource reservation. This requirement implies admission control to manage finite resources. IntServ nodes need to avoid accepting unauthorized requests or requests that can affect existing reservations with service commitments. Different types of users are expected to have different rights to reserve network resources. In addition, the network load has to be controlled to meet the quantitative specification of the service-quality commitments of existing flows. IntServ leaves the selection of the QoS to the application rather than the network. The architecture defines a flow as the basic service unit. This abstraction represents a distinguishable stream of packets that requires the same QoS. Flows are unidirectional. They have a single source and one or many destinations. IntServ requires the use of per- flow state in network nodes. This requirement results from the flow granularity and the use of resource reservation with admission control. Having network nodes maintaining per- flow state represents a significant change to the original IP architecture that left per-flow state to end systems. The architecture recommends the use of a signaling protocol to set up and refresh the state to preserve the robustness of the IP protocol. RFC 1633 introduces the architecture. Figure 1-1 shows a simple example of an IntServ network.
  • 26.
    6 Chapter 1:QoS Technology Overview Figure 1-1 Overview of a Network Implementing IntServ Service Model The IntServ architecture defines an extensible service model with a common framework. An important component of the definition of a service is the information that the receiver, which requests the service, must specify to the network.A service request includes a TSpec and, possibly, an RSpec. When a service request is accepted, the network nodes must guarantee the service as long as the TSpec continues to describe the flow. The combination of a TSpec and an RSpec receives the name of flowspec. The architecture service model uses a common TSpec definition. Four parameters characterize the traffic: • A token bucket (r, b)—The token bucket includes a token rate (r) and a token bucket size (b). • A peak rate (p)—Flow traffic may not arrive at a rate higher than the peak rate. • A minimum policed unit (m)—Network nodes treat packets of a size smaller than the minimum policed unit as packets of size m. This term facilitates the estimation of the actual bandwidth that a flow requires (including the Layer 2 header overhead). • A maximum packet size (M)—A node considers packets with a size larger than M as packets that do not conform to the traffic specification. Those nonconforming packets might not receive the same service as conforming packets. RSVP Endpoint RSVP Endpoint Flow Signaling Message RSVP State RSVP State RSVP State Signaling Message
  • 27.
    IP QoS Architectures7 Table 1-1 summarizes the TSpec parameters. NOTE The token bucket is an important concept in traffic management. The sections “Traffic Policing” and “Traffic Shaping” describe it in more detail later in this chapter. The architecture defined two services: Guaranteed Service (GS) and Controlled Load Service (CLS). They complement the best-effort service that is part of the definition of the IP protocol. IntServ does not introduce any changes to the operation of the best-effort service. In addition, the IntServ service model does not mandate a particular implemen- tation for the traffic-management mechanisms that implement a service. The next two sections explain the GS and CLS services, focusing on their end-to-end behavior and their flow specifications. NOTE RFC 2997 later defined a Null Service type. Applications can use this service to let the network determine the appropriate service parameters for the flow. This service type has special applicability for the integration of IntServ and DiffServ architectures. Guaranteed Service GS provides flows with a delay and bandwidth guarantee. GS ensures a firm bound on the maximum end-to-end queuing delay for packets that conform to the flowspec. Furthermore, a properly policed flow should not experience queuing drops in the absence of network failures or routing changes. The service does not consider fixed-delay components that are a property of the flow path (for example, propagation delay or serialization delay). A flow receives guaranteed service if all nodes along the path support the service. GS does not guarantee an average or minimum delay, just a maximum bound. Therefore, this service does not provide any jitter guarantees. RFC 2212 defines GS. Table 1-1 TSpec Parameters Parameter Description r Token rate b Token bucket size p Peak rate m Minimum policed unit M Maximum packet size
  • 28.
    8 Chapter 1:QoS Technology Overview A receiver provides a TSpec and an RSpec when requesting GS. The RSpec contains a service rate (R) and a time slack (S). Network nodes must approximate the service that a dedicated line at that rate would provide to the flow. Nodes make available the margin of error of their approximation. Applications can use this information to compute the maximum end-to-end delay that the flow will experience. The slack term in the RSpec specifies the incremental end-to-end delay that the sender can tolerate if a node modifies the flow resource allocation. Applications can adjust the flowspec if the delay bound is not acceptable. Table 1-2 summarizes the RSpec parameters. Control Load Service CLS approximates the behavior of best-effort service during unloaded conditions. Network nodes satisfy this behavior even in the presence of congestion.Applications can assume that the network will deliver a high percentage of all packets to their final destination. In addition, applications can assume that a high percentage of the delivered packets will experience a delay that will not greatly exceed the minimum delay of any packet. Applications do not receive any target values for packet delay or loss. This service supports those applications that operate satisfactorily with a best-effort service but are highly sensitive to congestion conditions. Applications do not require an RSpec to request CLS, only the flow TSpec. RFC 2211 introduces CLS. Use of RSVP in IntServ IntServ can use RSVP as the reservation setup protocol. One of the principles of this architecture is that applications communicate QoS requirements for individual flows to the network. These requirements are used for resource reservation and admission control. RSVP can perform this function. However, RSVP is frequently but inaccurately equated to IntServ. RSVP and IntServ share a common history, but they are ultimately independent. Two separate working groups at the IETF developed their specifications. RSVP has applicability as a signaling protocol outside IntServ. Similarly, IntServ could use other signaling mechanisms. The section “Resource Reservation Protocol” explains the protocol details later in this chapter. RFC 2210 describes how IntServ uses RSVP and defines the RSVP objects to implement the IntServ service model. Table 1-2 RSpec Parameters Parameter Description R Service rate S Time slack
  • 29.
    IP QoS Architectures9 Differentiated Services The DiffServ working group was responsible for the definition of this architecture at the IETF. The group met for the first time during the forty-first IETF in 1998. The working group was created with a charter to produce an architecture with a simple and coarse QoS approach that applied to both IPv4 and IPv6. The charter explicitly excluded microflow identification and signaling mechanisms (marking an explicit departure from the approach taken by IntServ). The working group produced 12 RFCs, with five of them being in the standards track and the rest being informational. The group eventually closed after its last meeting in 2001. NOTE An IP traffic stream with a unique combination of source address, destination address, protocol, source port, and destination port defines a microflow. DiffServ Terminology The DiffServ architecture introduces many new terms. This section presents a simplified definition of a selected few of them. The upcoming sections explain the terms in more detail. RFC 2475 and 3260 introduce the complete list of terms: • Domain—A network with a common DiffServ implementation (usually under the same administrative control). • Region—A group of contiguous DiffServ domains. • Egress node—Last node traversed by a packet before leaving a DiffServ domain. • Ingress node—First node traversed by a packet when entering a DiffServ domain. • Interior node—Node in a DiffServ domain that is not an egress or ingress node. • DiffServ field—Header field where packets carry their DiffServ marking. This field corresponds to the six most significant bits of the second byte in the IP header (formerly, IPv4 TOS [Type-of-Service] octet and IPv6 Traffic Class octet). • Differentiated Services Code Point (DSCP)—A specific value assigned to the DiffServ field. • Behavior aggregate (BA)—Collection of packets traversing a DiffServ node with the same DSCP. • Ordered aggregate (OA)—A set of BAs for which a DiffServ node must guarantee not to reorder packets. • BA classifier—Classifier that selects packets based on DSCP. • Multifield (MF) classifier—Classifier that selects a packet based on multiple fields in the packet header (for example, source address, destination address, protocol, and protocol port).
  • 30.
    10 Chapter 1:QoS Technology Overview • Per-hop behavior (PHB)—Forwarding behavior or service that a BA receives at a node. • Per-hop behavior group—One or more PHBs that are implemented simultaneously and define a set of related forwarding behaviors. • PHB scheduling class (PSC)—A set of PHBs for which a DiffServ node must guarantee not to reorder packets. • Traffic profile—Description of a traffic pattern over time. Generally, in terms of a token bucket (rate and burst). • Marking—Setting the DSCP in a packet. • Metering—Measuring of a traffic profile over time. • Policing—Discarding of packet to enforce conformance to a traffic profile. • Shaping—Buffering of packets to enforce conformance to a traffic profile. • Service level agreement (SLA)—Parameters that describe a service contract between a DiffServ domain and a domain customer. • Traffic-conditioning specification—Parameters that implement a service level specification. • Traffic conditioning—The process of enforcing a traffic conditioning specification through control functions such as marking, metering, policing, and shaping. NOTE This DiffServ section is consistent with the original architecture terms. Note, however, that Cisco documentation considers metering an implicit component of traffic shaping and policing. Furthermore, it regards dropping as just one of three possible actions (transmit, drop, mark) of a policer. The remainder of the book follows the policing and shaping definitions used in Cisco documentation. Architecture Principles The DiffServ architecture relies on the definition of classes of traffic with different service requirements. A marking in the packet header captures the traffic classification. Further network nodes inspect this marking to identify the packet class and allocate network resources according to locally defined service policies. The service characteristics are unidirectional with a qualitative description in terms of latency, jitter, and loss. DiffServ nodes are stateless from a QoS point of view and have no knowledge of individual flows. Relatively few packet markings are possible with respect to the number of microflows that a node may be switching at a given point in time. However, the concept of grouping or aggregating traffic into a small number of classes is inherent to DiffServ. The architecture intentionally makes a tradeoff between granularity and scalability. RFC 2475 introduces the architecture.
  • 31.
    IP QoS Architectures11 Providing different levels of service using aggregate classification and marking is not a novel concept. As an analogy, consider a transoceanic commercial flight with multiple classes of service. During the check-in process, the passenger needs to provide some identification information (classification criteria). Based on this information, the agent identifies the passenger class (for instance, first, business, or tourist) and provides a boarding pass that reflects the assigned class (marking). The customer class influences the service the passenger receives during the duration of the flight (including access to airline lounge, boarding priority, in-flight service, and deboarding priority). The reduced number of classes allows the airline to provide some differentiation to customers without having to provide a totally individualized service to each passenger. As you can probably recognize, this is not the only instance of aggregate classification and marking used in real life. Differentiated Services Code Point Previous specifications of the IP protocol had already reserved header bits for QoS purposes. The IP version 4 specifications in RFC 791 defined the second header octet as the TOS octet. Also, the IP version 6 specifications in RFC 2460 defined the second header octet as the Traffic Class octet but with an undefined structure. In the original TOS octet in IP version 4, the three most significant bits specified the packet precedence (an indication of the relative importance or priority). The next 3 bits in the TOS octet indicated the delay, throughput, and reliability requirements. The final two (least significant) bits were undefined and set to zero. RFC 1349 introduced a small change in the TOS octet by defining a field that included a cost bit plus the existing delay, throughput, and reliability bits. Similarly, the IP version 6 specifications in RFC 2460 define the second header octet as the Traffic Class octet but with an undefined structure. Figure 1-2 illustrates these now-obsolete definitions. The DiffServ architecture redefines the IPv4 TOS octet and the IPv6 Traffic Class octet. RFC 2474 and RFC 3260 name the DiffServ field as the six most significant bits in the previous IPv4 TOS and IPv6 Traffic Class octets. A particular value of the DiffServ field represents a DSCP. A DiffServ node services packets according to this code point. A group of packets sharing the same DSCP and traversing a link in a specific direction constitutes a BA. A class of traffic may include one or more BAs. The architecture defines three code point pools for the DiffServ field. Two pools, representing 32 out of the 64 possible values, are reserved for experimental or local use. The existing DiffServ specifications provide recommendations for 21 out of the 32 code points available in the third pool. The section “Per-Hop Behaviors” in this chapter introduces these values and their service definitions. Eight (class selector) code points provide backward compatibility with the previous Precedence field in the TOS octet. The DiffServ field does not provide any backward compatibility with the TOS field (delay, throughput, and reliability bits) previously defined in the TOS octet. Figure 1-3 shows the structure of the new DiffServ field, the code point pools, and the class selector code points.
  • 32.
    12 Chapter 1:QoS Technology Overview Figure 1-2 Previous Definitions of the TOS Octet for IPv4 and IPv6 That DiffServ Makes Obsolete Figure 1-3 DiffServ Field, Code Point Pools, and Class Selector Code Points Precedence D 0 1 2 3 4 5 6 7 T R 0 0 RFC 791 Precedence 111 – Network Control 110 – Internetwork Control 101 – CRITIC / ECP 100 – Flash Override 011 – Flash 010 – Immediate 001 – Priority 000 – Routine Delay (D) 0 – Normal 1 – Low Throughput (T) 0 – Normal 1 – High Reliability (R) 0 – Normal 1 – High T r a f f i c c l a s s 0 1 2 3 4 5 6 7 RFC 2460 Precedence 0 1 2 3 4 5 6 7 T O S 0 RFC 1349 Precedence 111 – Network Control 110 – Internetwork Control 101 – CRITIC / ECP 100 – Flash Override 011 – Flash 010 – Immediate 001 – Priority 000 – Routine TOS Field 1000 – minimize delay 0100 – maximize throughput 0010 – maximize reliability 0001 – minimize monetary cost 0000 – normal service D i f f S e r v F i e l d 0 1 2 3 4 5 6 7 RFC 2474 RFC 3260 DiffServ Field Codepoint Pools xxxxx0 – Standard xxxx11 – Experimental or local use xxxx01 – Future standard, experimental or local use DiffServ Codepoints 111000 – Class Selector 7 110000 – Class Selector 6 101000 – Class Selector 5 100000 – Class Selector 4 011000 – Class Selector 3 010000 – Class Selector 2 001000 – Class Selector 1 000000 – Class Selector 0
  • 33.
    IP QoS Architectures13 Nodes, Domains, and Regions The DiffServ architecture defines a hierarchy that goes from a single device, to a network, to a group of networks. A set of nodes with a common DiffServ implementation forms a domain. The nodes inside a domain perform similar service definitions and policies. A domain is typically under a single administrative control. A set of contiguous domains defines a DiffServ region. The domains within the region must be able to provide DiffServ to traffic traversing the different domains in the region. Individual domains may use different service definitions, policies, and packet markings. In those cases, the domains must have peering agreements that specify how traffic is handled when crossing domains. Boundary nodes and interior nodes constitute the two main types of nodes that reside in a DiffServ domain. Boundary nodes interface with the outside of the domain and ensure that any traffic is properly classified, marked, and within the agreed amounts. DiffServ defines these operations as traffic classification and conditioning. Boundary and interior nodes implement local service policies according to the packet marking. These local policies provide different levels of service to each BA that DiffServ calls PHBs. The section “Per- Hop Behaviors” discusses this concept in detail. A domain may have some nodes that do not support DiffServ. The service impact of these nodes depends on their number and their location within a domain. Figure 1-4 illustrates a DiffServ region with two domains. Traffic enters a domain at an ingress boundary node and leaves the domain at an egress boundary node. The ingress boundary node typically performs the traffic-classification and conditioning function according to a specification or contract. Boundary nodes generally act as both ingress and egress nodes because traffic differentiation is desirable for the traffic that flows in both directions. Traffic Classification and Conditioning Traffic classification and conditioning identifies the traffic that will receive a differentiated service and ensures that it conforms to a service contract. Outside nodes connecting to the DiffServ domain have agreed to some service terms that the architecture defines as an SLA. The boundary node enforces this SLA, or contract, using traffic classification and conditioning. This enforcement uses a combination of packet classification, marking, metering, shaping, and policing to ensure that the traffic conforms to the contract terms.
  • 34.
    14 Chapter 1:QoS Technology Overview Figure 1-4 Functional View of Nodes and Domains in a DiffServ Region NOTE RFC 3260 refined the initial DiffServ definition of SLA and introduced a new term, service level specification (SLS). Even though the term clarification is useful, this book uses the term SLA (which is more commonly used). Traffic classification is the first action that a boundary node performs on traffic entering the domain. The boundary node examines the packet and, according to the SLA terms, implements an appropriate action (for example, marking, metering, policing). The architecture describes two types of classifiers: BA classifier and MF classifier. The BA classifier classifies packets using the DSCP in the packet. The MF classifier classifies packets using one or more fields of the packet header (for example, source IP address, destination IP address, protocol, source port, destination port) and other packet information (for example, input interface). The final result of packet classification is the local association of each packet with a class. NOTE The DiffServ architecture did not consider packet payload as input for packet classification. Actual implementations support packet classification using payload inspection and other classification criteria.You can consider those classifiers as an extension of the MF classifiers. Region Direction of Traffic Flow Ingress Boundary Node Egress Boundary Node Interior Node Upstream Domain Downstream Domain Ingress Boundary Node Egress Boundary Node Interior Node
  • 35.
    IP QoS Architectures15 The boundary node conditions packets according to the SLA after classification. Traffic conditioning involves a combination of one or more of the following mechanisms: metering, marking, policing, or shaping. This conditioning process uses the result of the packet classification as input. Conditioning may vary from class to class. SLAs typically define a limit on the amount of traffic that the boundary node will take for each class. In those cases, the boundary node measures the traffic and makes a marking, dropping, or buffering decision on the packet. Conditioning must set the DSCP of each packet to an appropriate value. Downstream nodes typically rely on this DSCP for fast packet classification. The sections “Traffic Policing” and “Traffic Shaping” provide more details on conditioning mechanisms. Traffic classification and conditioning may happen at different points of a packet path. In general, boundary nodes perform these tasks. However, the architecture does not preclude interior nodes from doing complex classification and conditioning if needed (for example, on international links). Figure 1-5 shows an example in which the ingress boundary node of the upstream domain uses MF classifiers and conditions separately the traffic that A and B generate. Marking packets close to the source facilitates application differentiation and simplifies classification on downstream nodes. In this example, the ingress boundary node of the downstream domain conditions the aggregate traffic that it receives. The ingress node relies on the classification and marking that the upstream domain performed. The egress boundary nodes may also perform traffic conditioning. Figure 1-5 Illustration of SLA Enforcement Across Two DiffServ Domains Per-Hop Behaviors The DiffServ architecture defines a PHB as the forwarding behavior that a node applies to a BA. It represents a qualitative description of the latency, jitter, or loss characteristics that a BA will experience while traversing a DiffServ node. The PHB definition does not BA classification and aggregate conditioning enforce SLA between domains MF classification and conditioning enforce a separate SLA for each source. A B Ingress Boundary Node Egress Boundary Node Upstream Domain Downstream Domain Ingress Boundary Node Egress Boundary Node IP
  • 36.
    16 Chapter 1:QoS Technology Overview quantify these characteristics. A PHB group contains one or more related PHBs that are implemented simultaneously. DiffServ nodes map packets to PHBs according to their DSCP. Table 1-3 shows the mappings that the architecture specifications recommend. DiffServ does not mandate these DSCP-to-PHB mappings. It provides the flexibility to confiugure arbitrary mappings if desired. Class selectors are the only exception, because the architecture defines them for backward compatibility with the use of the Precedence field in the IPv4 TOS octet. DiffServ domains not using the recommended mappings are more likely to have to re-mark traffic when interfacing with other DiffServ domains and experience greater operational complexity. Table 1-3 IETF-Recommended Mapping Between PHBs and DSCPs PHB DSCP (Decimal) DSCP (Binary) EF 46 101110 AF43 38 100110 AF42 36 100100 AF41 34 100010 AF33 30 011110 AF32 28 011100 AF31 26 011010 AF23 22 010110 AF22 20 010100 AF21 18 010010 AF13 14 001110 AF12 12 001100 AF11 10 001010 CS7 56 111000 CS6 48 110000 CS5 40 101000 CS4 32 100000 CS3 24 011000 CS2 16 010000 CS1 8 001000 Default 0 000000
  • 37.
    IP QoS Architectures17 A number of PHB or PHB groups are part of the current DiffServ specifications: Expedited Forwarding (EF), Assured Forwarding (AF1, AF2, AF3, and AF4), Class Selector (CS), and Default. A node may support multiple PHB groups simultaneously. Nodes implement these PHBs using packet-buffering and scheduling mechanisms that the section “Traffic- Management Mechanisms” discusses. Expedited Forwarding The EF PHB defines a low-latency, low-jitter, and low-loss behavior that a DiffServ node may implement. This PHB acts as a building block for the transport of real-time traffic over a DiffServ domain. To support this behavior, a DiffServ node must serve EF traffic at a rate that is higher than its arrival rate, independently of the amount of non-EF traffic. This difference between the EF arrival and service rate helps ensure that EF traffic encounters empty or near-empty queues, which minimizes the queuing latency. This type of latency is generally the main contributor to packet latency and jitter during normal node operation. Minimization of queuing latency results in not only low latency and low jitter but also in low loss, because it prevents exhaustion of packet buffers. A DiffServ node should not cause any packet reordering within EF microflows. RFC 3246 and RFC 3247 define and discuss this PHB in detail. Assured Forwarding The AF family of PHB groups defines four different levels of forwarding guarantee that a DiffServ node may support. In simpler terms, these groups define how a DiffServ node may support different packet-loss guarantees. TheAF PHB groups receive the names:AF1,AF2, AF3, and AF4. Each of these groups supports three drop-precedence levels. The higher the drop precedence, the more likely a DiffServ node will drop the packet if the group exhausts its allocated resources (bandwidth and buffers). A total of 12 PHBs are associated with AF. Table 1-4 lists these PHBs with their respective drop precedence. RFC 2597 provides the detailed specifications for this set of PHB groups. The AF PHB groups operate independently of each other. No implied ordering of forwarding guarantee exists between them. Furthermore,AF groups do not have an implicit latency or jitter characterization. The actual guarantees provided by each group depend on the forwarding resources that the node allocated, the amount of traffic of that group arriving Table 1-4 AF PHBs and Their Respective Drop Precedence Drop Precedence AF1 AF2 AF3 AF4 Low AF11 AF21 AF31 AF41 Medium AF12 AF22 AF32 AF42 High AF13 AF23 AF33 AF43
  • 38.
    18 Chapter 1:QoS Technology Overview at the node, and the relative drop precedence of the packet. The resources the node allocates are bandwidth and buffering space. The specifications mandate that nodes forward with higher probability those packets within an AF group that have lower drop precedence. A DiffServ node must not reorder packets of the same microflow within an AF group. Class Selectors DiffServ defines CS PHBs to offer backward compatibility with the use of IP precedence in the IPv4 TOS octet. Class selectors maintain the same relative ordering of IP precedence (a higher value implies a higher relative order). A node should provide a higher probability of forwarding to higher CSs. There is no latency, jitter, or loss characterization. Table 1-5 shows the mapping between CSs and IP precedence. Default PHB A DiffServ domain must provide a Default PHB that offers best-effort service. More precisely, the architecture defines the Default PHB as the existing best-effort service that RFC 1812 specifies. That is, the DiffServ domain will forward as many packets as possible, as soon as possible. There is no latency, jitter, and loss characterization. The implementation of other PHBs should preclude the operation of applications that rely on best-effort service. MPLS Support for IntServ MPLS support for IntServ remains undefined. The fact that RSVP can perform MPLS label distribution does not imply support for IntServ. As mentioned previously, the IntServ architecture makes use of RSVP, but the protocol signaling capabilities go beyond the IntServ requirements. However, you can find current efforts at the IETF to specify the Table 1-5 Relationship Between IP Precedence Values and DiffServ CSs PHB DSCP (Decimal) DSCP (Binary) Precedence Name Precedence (Binary) Precedence (Decimal) CS7 56 111000 Network Control 111 7 CS6 48 110000 Internetwork Control 110 6 CS5 40 101000 Critic/ECP 101 5 CS4 32 100000 Flash Override 100 4 CS3 24 011000 Flash 011 3 CS2 16 010000 Immediate 010 2 CS1 8 001000 Priority 001 1 CS0 0 000000 Routine 000 0
  • 39.
    MPLS Support forDiffServ 19 interaction of aggregate IntServ reservations with MPLS networks. This proposal allows aggregate reservations to take advantage of the capabilities of MPLS networks without forcing those networks to provide full IntServ support. The “References” section at the end of this chapter lists reading material on the subject that currently constitutes work in progress. MPLS Support for DiffServ MPLS supports DiffServ with minimal adjustments to the MPLS and DiffServ architectures. MPLS does not introduce any modifications to the traffic-conditioning and PHB concepts defined in DiffServ. A label switching router (LSR) uses the same traffic-management mechanisms (metering, marking, shaping, policing, queuing, and so on) to condition and implement the different PHBs for MPLS traffic. An MPLS network may use traffic engineering to complement its DiffServ implementation. RFC 3270 defines MPLS support for the DiffServ architecture. An MPLS network may implement DiffServ to support a diverse range of QoS requirements and services in a scalable manner. MPLS DiffServ is not specific to the transport of IP traffic over an MPLS network. An MPLS network may be carrying other types of traffic for which DiffServ does not apply (for example, ATM or Frame Relay). An MPLS DiffServ implementation is concerned only with supporting the PHBs that can satisfy the QoS requirements of all the types of traffic it carries. In addition, an MPLS network can grow without having to introduce major changes to its DiffServ design as the number of label switched paths (LSPs) in the network increases. These characteristics play an important role in the implementation of large MPLS networks that can transport a wide spectrum of traffic. MPLS support for DiffServ introduces two types of LSPs with different service characteristics and operation. The first type, EXP-inferred-class LSP (E-LSP), can transport simultaneously multiple classes of traffic. The second type, Label-inferred-class LSP (L-LSP), transports a single class. They rely on different mechanisms to encode the DiffServ marking of the packet. In general, MPLS uses a label stack encoding based on shim headers that RFC 3032 defines. Figure 1-6 illustrates the fields contained in the shim header. The specifications for MPLS DiffServ define two encodings for the DiffServ code point. In addition, these LSP types impose different LSP signaling requirements. The changes in the encoding of DiffServ marking and the use of signaling are the two important areas where MPLS DiffServ differs from the original specification. NOTE RFC 3270 formally defines E-LSPs as EXP-inferred-PSC LSPs and L-LSP as Label-only- inferred-PSC LSPs. The section “DiffServ Terminology” provided a formal definition of a PSC earlier in this chapter. You can simply equate the term to a class of traffic.
  • 40.
    20 Chapter 1:QoS Technology Overview Figure 1-6 MPLS Shim Header NOTE ATM LSRs, Frame Relay LSRs, and LSRs with label switching controlled ATM (LC-ATM) interfaces use a native encoding for the top label rather than the shim header. This has important implications for the implementation of DiffServ on those devices. Given their decreasing use, this book does not focus on their details. E-LSP MPLS support for DiffServ defines E-LSP as a type of LSP that can carry simultaneously multiple classes of traffic. LSRs use the EXP field in the shim header to infer the PHB that a packet requires. As Figure 1-6 shows, the EXP contains three bits that can take eight possible values. The size of this field implies that an E-LSP can transport up to eight classes of service. An E-LSP carries fewer classes if some of those classes consume multiple markings (for example, AF1 which may use two or three markings). The specifications do not define recommended EXP values for the existing DiffServ PHBs (EF, AFn, CSn, Default). Furthermore, they do not define any structure on the three-bit field. LSRs may set up E-LSPs with bandwidth reservation (generally for the purpose of admission control). Figure 1-7 illustrates a network using E-LSPs. In this case, there are two E-LSPs between node A and D. The network supports three classes: EF, AF1, and AF2. From top to bottom, the first E-LSP carries EF traffic; the second LSP multiplexes traffic of the three classes. Even though E-LSPs may carry multiple classes, the first E-LSP transports only EF traffic in this scenario.According to the E-LSP rules, all nodes perform PHB determination based on the EXP value of the packet. Notice that some EF traffic follows one E-LSP, whereas the rest follows the other E-LSP. Node A can split EF traffic if the node does not split EF microflows. Node C serves EF traffic without consideration of what LSP carries the EF traffic. Label EXP TTL S 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 MPLS Shim Header Label: MPLS Label Value EXP: Experimental Use S: Bottom of Stack TTL: Time to Live RFC 3032
  • 41.
    MPLS Support forDiffServ 21 Figure 1-7 MPLS Network Using an E-LSP MPLS support for DiffServ defines mechanisms for E-LSPs to signal mappings between EXP values and PHBs. An LSR associates EXP-to-PHB mappings for input labels and PHB-to-EXP mappings for output labels. Signaling is optional and takes place during LSP setup. RFC 3270 defines extensions to LDP (DiffServ TLV [Type, Length, Value] for Label Request, Label Mapping, Label Release, and Notification messages) and RSVP (DiffServ object for Path messages) and their appropriate processing. The signaling identifies the LSP as an E-LSP and specifies the mappings between EXP values and PHBs that it will use. LSRs can use static but configurable mappings to avoid these signaling extensions for E-LSPs. An LSR should map all EXP values to the Default PHB if the LSP signaling did not specify a mapping and no preconfigured mapping exists. NOTE ATM LSRs, Frame Relay LSRs, and LSRs with LC-ATM interfaces do not forward packets using an MPLS shim header encapsulation. The absence of a shim header implies the absence of the EXP field. Therefore, those devices cannot support E-LSPs. This restriction also applies to nonpacket networks that use generalized MPLS (GMPLS). IP/MPLS C B D A EF Packet AF1 Packet AF2 Packet
  • 42.
    22 Chapter 1:QoS Technology Overview L-LSP MPLS support for DiffServ defines L-LSP as a type of LSP that can only transport of a single class of traffic. LSRs infer the class associated with the a packet from the label and determine the exact PHB using the label in combination with the EXP field. Table 1-6 illustrates the mandatory mapping between <classes, EXP> and PHBs. LSRs learn the association between L-LSP labels and classes during LSP setup. L-LSPs require the use of DiffServ signaling extensions. In this case, LSRs use a different format of the LDP DiffServ TLV and RSVP DiffServ object. The signaling identifies the LSP as an L-LSP and specifies the class that the L-LSP will transport. As with E-LSPs, LSRs may set up L-LSPs with bandwidth reservation. Table 1-6 Mandatory PHB Mappings for L-LSPs Class EXP (Decimal) EXP (Binary) PHB EF 0 000 EF AF4 3 011 AF43 AF4 2 010 AF42 AF4 1 001 AF41 AF3 3 011 AF33 AF3 1 010 AF32 AF3 3 001 AF31 AF2 2 011 AF23 AF2 1 010 AF22 AF2 3 001 AF21 AF1 2 011 AF13 AF1 1 010 AF12 AF1 1 001 AF11 CS7 0 000 CS7 CS6 0 000 CS6 CS5 0 000 CS5 CS4 0 000 CS4
  • 43.
    MPLS Support forDiffServ 23 Figure 1-8 illustrates an MPLS network using L-LSPs. In this case, there are four L-LSPs between node A and D. The network supports three classes: EF, AF1, and AF2. From top to bottom, the first L-LSP carries AF2, the second and third ones carry EF, and the fourth and last L-LSP carries AF1 traffic. Notice that node A splits EF traffic over two L-LSPs. Node A can divide EF traffic if the node does not split EF microflows. Even though Node C identifies EF traffic using the labels, that node serves EF traffic without consideration of what L-LSP is carrying the traffic (that is, the node does not provide a PHB per L-LSP, but per class). Figure 1-8 MPLS Network Using L-LSPs The use of E-LSPs and L-LSPs on an MPLS network is not mutually exclusive. LSRs maintain a DiffServ label context. This context indicates the LSP type (E-LSP or L-LSP), the PHBs that the LSP supports, and a mapping between the packet encapsulation and a PHB. For input labels, that mapping defines how the LSR can infer the PHB from the packet encapsulation. For output labels, that mapping defines how the LSR encodes the PHB. This Class EXP (Decimal) EXP PHB CS3 0 000 CS3 CS2 0 000 CS2 CS1 0 000 CS1 Default 0 000 Default Table 1-6 Mandatory PHB Mappings for L-LSPs (Continued) IP/MPLS C B D A EF Packet AF1 Packet AF2 Packet
  • 44.
    24 Chapter 1:QoS Technology Overview context is populated with preconfigured mappings or through DiffServ information learned during LSP setup. Table 1-7 compares E-LSPs and L-LSPs. Figure 1-9 shows an MPLS network using L-LSPs and E-LSPs simultaneously. In this example, there are two E-LSPs between node E and node D and two L-LSPs between node A and D. The network supports three classes: EF, AF1, and AF2. In this example, node C transports both E-LSPs and L-LSPs. This node uses the DiffServ label context to determine the LSP type and the exact mapping that it should use to infer the PHB from the packet encapsulation. LSRs serve the packets according to their PHB regardless of the LSP and its type. The LSP details influence the PHB determination, but the PHB ultimately determines the packet treatment. In this example, nodes A and E use one type of LSPs exclusively. However, each of them could alternatively use a combination of E-LSPs and L-LSPs to reach node D. Figure 1-9 MPLS Network Combining L-LSPs and E-LSPs Table 1-7 Comparing E-LSPs and L-LSPs E-LSP L-LSP One or more classes per LSP One class per LSP PHB inferred from EXP field PHB inferred from Label and EXP field Signaling optional Signaling required IP/MPLS C B D A E EF Packet AF1 Packet AF2 Packet E-LSP L-LSP
  • 45.
    MPLS Support forDiffServ 25 NOTE ATM LSRs, Frame Relays LSRs, and LSRs with LC-ATM interfaces do not forward packets using an MPLS shim header encapsulation. The absence of a shim header implies the absence of the EXP field. However, those devices can still support DiffServ using their native encapsulation to implement L-LSPs.ATM LSRs and LSRs with LC-ATM interfaces use the native label encoding and the ATM CLP (Cell Loss Priority) bit for PHB determination. Frame Relay LSRs use their native label encoding and the Frame Relay DE bit for PHB determination. RFC 3270 describes in detail the procedures that apply in those cases. DiffServ Tunneling Models over MPLS MPLS LSPs support for DiffServ defines three models of interaction between DiffServ markings in different layers of encapsulation. A simple example is an IP packet that has received the MPLS encapsulation. There is one PHB marking in the MPLS encapsulation and a PHB marking in the DiffServ field of the IP packet. There are three models to handle the interaction between multiple markings: the pipe, short-pipe, and uniform models. The models define the procedures that an LSR can apply when a packet (either IP or MPLS) with an existing PHB marking enters and exits an LSP. The three models do not introduce any changes to the normal label swapping behavior of an LSR or any signaling requirements. These models apply equally to E-LSPs and L-LSPs. NOTE The MPLS DiffServ tunneling models extend the concepts introduced in RFC 2983. That RFC defines the operation of DiffServ over IP tunnels. In many aspects, LSPs resemble IP tunnels. NOTE RFC 3270 defines the MPLS DiffServ tunneling models for the transport of IP and MPLS traffic. However, the underlying concepts can apply to the transport of other types of traffic (for example, Ethernet) over an MPLS network. Pipe Model The pipe model conceals the tunneled PHB marking between the LSP ingress and egress nodes. This model guarantees that there are no changes to the tunneled PHB marking through the LSP; even if an LSR along the path performs traffic conditioning and re-marks the traffic. All LSRs that the LSP traverses use the LSP PHB marking and ignore the tunneled PHB marking. This model proves useful when an MPLS network connects other DiffServ domains. The MPLS network can implement DiffServ and still be transparent for the connected domains. RFC 3270 defines this model as mandatory for MPLS networks supporting DiffServ.
  • 46.
    26 Chapter 1:QoS Technology Overview Figure 1-10 illustrates the operation of the pipe model. The LSP ingress determines the LSP PHB marking it will encode in the pushed encapsulation. It may consider the existing PHB marking of the packet for this purpose. It preserves the tunneled PHB marking when pushing the new label encapsulation. Be aware that the packet entering the LSP may be an IP or an MPLS packet. The LSP egress serves the packet according to the LSP PHB marking. This action implies that this node infers the packet PHB before the pop operation. Moreover, the LSP egress does not modify the tunneled PHB marking that the pop operation exposes. An LSP using the pipe model cannot use penultimate hop popping (PHP) because the LSP egress will not have access to the LSP PHB marking. Figure 1-10 Pipe Tunneling Model Short-Pipe Model The short-pipe model represents a small variation of the pipe model. It also guarantees that there are no changes to the tunneled PHB marking, even if an LSR re-marks the LSP PHB marking. The short-pipe model shares the same ability of the pipe model to allow an MPLS network to be transparent from the DiffServ point of view. The short-pipe model differs, however, on how the LSP egress infers the packet PHB. The LSP egress uses the tunneled PHB marking to infer the packet PHB and serve the packet consequently. Given this difference with the pipe model, an MPLS network may implement LSPs using the short- pipe model regardless of whether LSRs perform PHP. Label Label IP/MPLS LSP Ingress LSP Egress LSP PHB Marking IP or MPLS Packet Tunneled PHB Marking Push Pop LSP PHB Marking Defines Packet PHB
  • 47.
    MPLS Support forDiffServ 27 Figure 1-11 demonstrates the details of the operation of the short-pipe model with PHP. The LSP ingress must determine the LSP PHB marking it will encode in the pushed encapsulation. It may consider the existing PHB marking of the packet. The LSP ingress also preserves tunneled PHB marking when pushing the new label encapsulation. The short-pipe and pipe models share the same procedure for the LSP ingress. It infers the packet PHB from the LSP PHB marking before performing the pop operation. The penultimate hop does not modify the tunneled PHB marking that the pop operation exposes. The LSP egress infers the packet PHB from the tunneled PHB marking in the header used for packet forwarding. Figure 1-11 Short-Pipe Tunneling Model with PHP Figure 1-12 shows the details of the short-pipe model for LSPs that do not experience PHP. The operation of the LSP ingress remains the same as before. The penultimate hop performs the label swapping operation and serves the packet according to the corresponding E-LSP or L-LSP procedures. The LSP egress infers the packet PHB from the tunneled PHB marking in the header used for packet forwarding. This action implies that the LSP egress infers the packet PHB after the label pop. As with all previous models, this node forwards the tunneled PHB marking unmodified. The short-pipe model offers the external behavior regardless of whether PHP happens. Label Label IP/MPLS LSP Ingress LSP Egress Penultimate Hop LSP PHB Marking IP or MPLS Packet Tunneled PHB Marking Push Pop LSP PHB Marking Defines Packet PHB Tunnel PHB Marking Defines Packet PHB
  • 48.
    28 Chapter 1:QoS Technology Overview Figure 1-12 Short-Pipe Tunneling Model Without PHB Uniform Model The uniform model makes the LSP an extension of the DiffServ domain of the encapsulated packet. In this model, a packet only has a single meaningful PHB marking (which resides in the most recent encapsulation). LSRs propagate the packet PHB to the exposed encap- sulation when they perform a pop operation. This propagation implies that any packet re-marking is reflected on the packet marking when it leaves the LSP. The LSP becomes an integral part of the DiffServ domain of the packet as opposed to the transparent transport that the pipe and short-pipe models provided. This model proves useful when an MPLS network connects other DiffServ domain and all networks (including the MPLS network) need to behave as a single DiffServ domain. Label Label IP/MPLS LSP Ingress LSP Egress LSP PHB Marking IP or MPLS Packet Tunneled PHB Marking Push Pop Tunneled PHB Marking Defines Packet PHB
  • 49.
    MPLS Support forDiffServ 29 Figure 1-13 illustrates the operation of the uniform model with PHP. The LSP ingress encodes the existing packet PHB marking in the pushed encapsulation. When the packet receives the new encapsulation, the encapsulated PHB marking becomes irrelevant. The penultimate hop infers the packet PHB before the pop operation and encodes it in the exposed encapsulation. Figure 1-13 Uniform Tunneling Model with PHP Figure 1-14 shows the details of the uniform model for LSPs without PHP. The operation of the LSP ingress remains the same. The penultimate hop performs a regular label swapping operation. The LSP egress always infers the PHB before the pop operation and propagates the PHB marking to the exposed encapsulation. The uniform model offers the same external behavior regardless of whether the LSP uses PHP. Tables 1-8 and 1-9 summarize the operation of the three tunneling modes with PHP and without PHP, respectively. Label Label IP/MPLS LSP Ingress LSP Egress Penultimate Hop LSP PHB Marking IP or MPLS Packet Push Pop LSP PHB Marking Defines Packet PHB (Propagated Down)
  • 50.
    30 Chapter 1:QoS Technology Overview Figure 1-14 Uniform Tunneling Model Without PHP Table 1-8 DiffServ Tunneling Models over MPLS with PHP Model LSP Ingress Penultimate Hop LSP Egress Pipe Not possible. Not possible. Not possible. Short-pipe Preserve tunneled PHB and set PHB in pushed encapsulation. Determine PHB before pop. Determine PHB using forwarding header. Uniform Copy existing packet PHB to pushed encapsulation. Determine PHB before pop and propagate it down. Determine PHB using received header. Table 1-9 Tunneling Models over MPLS Without PHP Model LSP Ingress LSP Egress Pipe Preserve tunneled PHB and set PHB in pushed encapsulation. Determine PHB before pop operations. Short-pipe Preserve tunneled PHB and set PHB in pushed encapsulation. Determine PHB after pop using forwarding header. Uniform Copy existing packet PHB to pushed encapsulation. Determine PHB before pop and propagate it down. Label Label IP/MPLS LSP Ingress LSP Egress LSP PHB Marking IP or MPLS Packet Push Pop LSP PHB Marking Defines Packet PHB (Propagated Down)
  • 51.
    Traffic-Management Mechanisms 31 Traffic-ManagementMechanisms The implementation of QoS ultimately relies on a collection of traffic-management mechanisms. The evolution of packet switched networks introduced the need for the development of suitable traffic-management mechanisms. These mechanisms help network nodes avoid and manage congestion. Frame Relay and, especially,ATM networks make use of some of these or similar techniques. This section summarizes the key concepts behind traffic management within the context of IP and MPLS networks. These mechanisms represent the building blocks that network nodes use to implement QoS using both the DiffServ and IntServ architectures. Traffic Classification Network nodes generally perform traffic classification before applying traffic-management mechanisms. The aggregate traffic that traverses a node typically combines traffic with different QoS requirements. In those cases, network nodes need to classify the traffic to provide the expected level of differentiation. Traffic classification can be in the form of an MF or BA classifier in the context of DiffServ. Classification can also be in the form of filter specification in IntServ. Traffic classification typically involves stateless inspection of packet headers. In some cases, nodes perform packet payload inspection or even stateful inspection of packets. However, the complexity and processing impact of those two types of classification limits its applicability to particular devices in the network. Traffic Marking Packet marking involves assigning a new value to a QoS-related field in the header of a packet. This marking typically associates the packet with a class or a drop precedence. As discussed earlier, the DiffServ architecture relies on packet marking to indicate the PHB for each packet. Several Layer 2 technologies also make use of packet marking for QoS purposes, as follows: • Ethernet uses a 3-bit priority field in the VLAN header. • ATM uses a 1-bit field to indicate the drop precedence of a cell (cell loss priority or CLP). • Frame Relay uses an equivalent 1-bit field to capture the drop precedence of a frame (Discard Eligible or DE).
  • 52.
    Exploring the Varietyof Random Documents with Different Content
  • 53.
    yellow. S. anemonæflòrais of various colours, and very similar to Anemòne. Tritònia, a genus of about twenty-five species. Few of them deserve culture in regard to their beauty. T. crocàta is in our collections, as I. crocàta, which is amongst the finest, and T. zanthospìla has white flowers curiously spotted with yellow. Watsònia, a genus containing several species of showy flowers, several of which are in our collections, under the genus Gladíolus, but the most of the species may easily be distinguished from it by their flat shell formed bulbs. W. iridifòlia is the largest of the genus, and has flowers of a flesh colour. W. ròsea is large growing, the flowers are pink, and on the stem in a pyramid form. W. humilis is a pretty red flowering species. W. fúlgida, once Antholyza fúlgens, has fine bright scarlet flowers. W. rùbens is an esteemed red flowering species, but scarce. These six genera are in general cultivation. There are several of others of merit that our limits will not admit of inserting. We have no doubt there are some splendid species that have not come under our observation, and others which may be obtained from the Cape of Good Hope not known in any collection. Many hundreds of superb bulbs indigenous to that country, and of the same nature and habit of the above, have not been seen in collections. The flowers of those which we have specified are from one to four inches in diameter, ringent, tubular, or campanulate. Pots from four to seven inches diameter, according to the size of the roots, will be large enough. Give them very little water until they begin to grow; then supply moderately, and keep them near the light. Of the Holland or Dutch bulbs, the Hyacinth is the favourite to bloom in the Green-house. A few of the Tulip, Narcissus, Iris, and Crocus, may for variety be also planted with any other that curiosity may dictate. When these are grown in pots, the soil should be four-eighths loam, two-eighths leaf mould, one-eighth decomposed manure, one-eighth sand, well compounded; plant in pots from four to seven inches, keep the crown of the bulb above the surface of the soil, except of the Tulip,
  • 54.
    which should becovered two inches. When these roots are potted, plunge them in the garden about three inches under ground; mark out a space sufficient to contain them; throw out the earth about four inches deep, place the pots therein, covering them with earth to the above depth, making it in the form of a bed. Leave a trench all round to carry off the rain. By so doing, the bulbs will root strong, the soil will be kept in a congenial state about them, and they will prove far superior than if done in the common method. Lift them from this bed on the approach of frost, or not later than the second week of December, wash the pots and take them to the Green- house. OF REPOTTING. Vibúrnum. This is a good period to repot all the flowering plants of this genus. For a full description of them, see Green-house, March. The repotting is only intended for young plants that are wanted to grow freely. When the V. tìnus is much encouraged, it does not flower profusely. Lìlium, Lily. There are four species of this splendid genus kept in the Green-house. It has always been our practice to repot them when they begin to grow, though it is said by some that, when removed at that time, they will not flower perfectly. They will not do to be kept above a few weeks out of the ground, and we think they ought never to be kept out any period. We place them here, that a choice may be made by the cultivator of either of the periods, which is not material; observing in either case, that excess of moisture is injurious while they are dormant. L. longiflòrum grows about one foot high, with one or more flowers. L. longiflòrum suavèolens, is sweet-scented, and has only one flower. L. japònicum is the most magnificent, grows about two feet high, with three or more flowers on one stem. L. lancifòlium; we incline to class this with L. speciòsum, there being no apparent distinction in any character. The flowers are all of the purest white. They require from five to seven inch pots.
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    Flower Garden. SEPTEMBER. OF DAHLIAS. Seethat all these plants are supported with proper stakes, rods, &c., that the wind may have no effect in breaking down or otherwise destroying the flower stems. Strictly observe their respective heights and colours, that they may be duly disposed and interspersed next year, if not done so this. If the early part of the month is dry, give them liberal supplies of water. GENERAL CARE OF PLANTS IN POTS. All the flowers that are in pots, and intended to be kept in frames during winter, should have a top-dressing, and a general preparation for their winter quarters, by tieing up, &c. The carnation and pink layers that were lifted and potted last month must be brought from the shade as soon as they begin to grow; and those that are not lifted, have them done forthwith, that they may be rooted afresh before the frost sets in. All Wall-flowers and Stocks should be lifted this month, and planted in five to seven inch pots, and treated as directed for carnation layers last month, until they begin to grow, when they must be fully exposed. PREPARE BEDS AND BORDERS FOR BULBOUS ROOTS. Bulbous roots of every character delight in deep free soil; consequently, wherever they are desired to be planted, due attention must be paid to put the soil in proper order, to have them in
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    perfection. Where thereare a quantity intended to be planted, to have them in beds is the general and preferable method. These ought to be dug from eighteen inches to two feet deep, at the bottom of which place three or four inches of decayed manure. Where the soil is poor it should be enriched with well decomposed manure and earth from the woods, incorporating both well with the soil, breaking it all fine. This being done, allow it to stand until the middle of next month, which see for farther directions. GENERAL OBSERVATIONS. Tie up carefully all the Chrysánthemums, Tuberoses, &c. Clear away the stems or haulm of any decayed annuals or herbaceous plants, that nothing unsightly may appear. Be attentive to the collecting of all kinds of seeds.
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    Rooms. SEPTEMBER. Where there isa quantity of plants to be kept in these apartments, they should be disposed to the best effect, and at the same time in such a manner as will be most effectual to their preservation. A stage of some description is certainly the best, and, of whatever shape or form, it ought to be on castors, that it may, in severe nights of frost, be drawn to the centre of the room. The shape may be either concave, a half circle, or one square side. The bottom step or table should be six inches apart, keeping each successive step one inch farther apart, to the desired height, which may be about six feet. Allowing the first step to be about two feet from the floor, there will be five or six steps, which will hold about fifty pots of a common size. A stage in the form of half a circle will hold more, look the handsomest, and be most convenient. We have seen them circular, and when filled appeared like a pyramid. These do very well, but they must be turned every day, or the plants will not grow regularly. With this attention it is decidedly the best. Green is the most suitable colour to paint them. GENERAL OBSERVATIONS. The directions given for the Green-house this month are equally applicable here. The Tasseled White Chrysanthemum, and a few other late blooming sorts, are particularly adapted for rooms. If there is no convenience to plunge the pots with Dutch bulbs in the garden, as described in the Green-house of this month, give them very little water until they begin to grow.
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    Hot-House. OCTOBER. Very few directionsremain to be given to the department of the Hot-house. The supplies of water for this and the two preceding months are, according to the state and nature of tropical plants, more limited than at any other period of the year. This is the first month of what may be called their dormant state. Observe the herbaceous plants, that they are, as soon as their foliage decays, set aside, in case of being too liberally supplied with water. Airing is highly essential about this period, that the plants may be gradually hardened; but guard against injuring them. The temperature should not be under fifty degrees; when the days are cool, and the wind chilling, airing is not necessary; and when air is admitted, always close up early in the afternoon, whilst the atmosphere is warm, to supersede the necessity of fire as long as possible. If at any time you have recourse to it in this month, use it with great caution. Examine all the shutters and fastenings, and see that they are in good substantial order, and where deficient repair them instantly, that they may be in readiness. Remove all leaves, and give syringings twice a week. Clear off, sweep out, and wash clean, that every part may be in the neatest order.
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    Green-House. OCTOBER. OF TAKING INAND ARRANGING THE PLANTS. As observed in the previous month, let the housing of Green- house plants now be attended to. Have all in before the eighth of the month, except a few of the half hardy sorts, which may stand until convenient. Begin by taking in all the tallest first, such as Oranges, Lemons, Myrtles, Oleanders, &c. Limes ought to be kept in the warmest part of the house, otherwise they will throw their foliage. In arrangement, order is necessary to have a good effect; and in small houses it ought to be neat and regular, placing the tallest behind, and according to their size graduating the others down to the lowest in front. Dispose the different sorts in varied order over the house, making the contrast as striking as possible. Having the surface of the whole as even as practicable, with a few of the most conspicuous for shape and beauty protruding above the mass, which will much improve the general appearance, and greatly add to the effect. All succulents should be put together. They will do in a dark part of the house, where other plants would not grow, studying to have the most tender kinds in the warmest part, and giving gentle waterings every three or four weeks. When all are arranged, give them a proper syringing, after which wipe clean all the stages, benches, &c. sweeping out all litter, and wash clean the pavement, which will give to all a neat and becoming appearance. Let the waterings now be done in the mornings, as often and in such quantities as will supply their respective wants, examining the plants every day.
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    During the continuanceof mild weather, the circulation of air must be as free as possible, opening the doors and front and top sashes regularly over the house. But observe in frosty nights, and wet, cloudy weather, to keep all close shut. Be attentive in clearing off decayed leaves and insects. Any plants of Lagerstræmia, Stercùlia, Hydrángea, Pomegranate, and others equally hardy, that are deciduous, may be kept perfectly in a dry, light, airy cellar, giving frequent admissions of air. OF REPOTTING. Anemònes. Where A. nemoròsa flòre plèno and A. thalictròides flòre plèno are kept in pots in the Green-house, they should be turned out of the old earth, and planted in fresh soil. They are both pretty, low growing, double white flowering plants, and require a shaded situation. The latter is now called Thalíctrum anemonoídes. Dáphne, is a genus of diminutive shrubs, mostly evergreens, of great beauty and fragrance. Very few species of them are in our collections. D. odòra, frequently called D. índica, is an esteemed plant for the delightful odour of its flowers, and valuable for the period of its flowering, being from December to March, according to the situation; leaves scattered, oblong, lanceolate, smooth; flowers small, white, in many-flowered terminale heads. D. hybrida is a species in high estimation at present in Europe, but little known here, being only in a few collections; flowers rose-coloured, in terminale heads, and lateral bunches in great profusion, and very similar to the former in habit and shape of flower; blooms from January to May, and is of a peculiar fragrance. D. oleoídes is what may be termed "ever-blooming;" flowers of a lilac colour; leaves elliptic, lanceolate, smooth. D. laurèola, Spurge laurel; D. póntica, D. alpìna, and D. Cneòrum, are all fine species, and in Europe are esteemed ornaments in the shrubbery, but we are not certain if they will prove hardy in our vicinity.
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    Prímula. There area few fine species and varieties in this genus, adapted either for the Green-house or Rooms. All the species and varieties will keep perfectly well in a frame, except the China sorts. Having previously observed a few of the other species and varieties, we will observe the treatment of these. P. sinénsis, now prænitens, known commonly as China Primrose; flowers pink, and in large proliferous umbels, flowering almost through the whole year, but most profusely from January to May. Keep them in the shade, and be careful that they are not over-watered during summer. As the stems of the plant become naked, at this repotting a few inches should be taken off the bottom of the ball, and placing them in a larger pot will allow the stems to be covered up to the leaves. P. p. albiflòra, colour pure white and beautiful. P. p. dentiflòra. There is also a white variety of this, both similar to the two former, only the flower indented. All these require the same treatment. As they only live a few years, many individuals, to propagate them, divide the stems, which in most cases will utterly destroy them. The best, and we may say the only method to increase them, is from seed, which they produce in abundance every year. Pæonia, is a magnificent genus. There are four varieties of them, half hardy and half shrubby. They will bear the winter if well protected, but are better in the Green-house. These are P. moután, Tree Pæony; the flower is about four inches in diameter, of a blush colour, and semi-double; P. M. Bànksii is the common Tree Pæony, and called in our collection P. Moutàn; it has a very large double blush flower, and is much admired. P. M. papaveràcea is a most magnificent variety; has large double white flowers, with pink centres; P. M. ròsea is a splendid rose-coloured double variety, and is scarce. These plants ought not to be exposed to the sun while in flower, as the colours become degenerated, and premature decay follows. If the Dutch bulbs intended for flowering during winter are not potted, have them all done as soon as possible, according to directions given last month.
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    CAMELLIAS. These plants oughtto have a thorough examination, and those that were omitted in repotting before they commenced growing, may be done in the early part of this month; but it is not adviseable, except the roots are matted round the ball of earth, which should be turned out entire. Examine all the pots, stir up the surface of the earth, and take it out to the roots, supplying its place with fresh soil. Destroy any worms that may be in the pots, as they are very destructive to the fibres. Look over the foliage and with a sponge and water clear it of all dust, &c. Frequently the buds are too crowded on these plants, especially the Double white and Variegated. In such case pick off the weakest, and where there are two together, be careful in cutting, so that the remaining bud may not be injured. This is the best period of the year to make selections of these, as they now can be transported hundreds of miles without any material injury, if they are judiciously packed in close boxes. In making a choice of these, keep in view to have distinctly marked varieties, including a few of those that are esteemed as stocks for producing new kinds, which are undoubtedly indispensable; and will reward the cultivator in a few years with new sorts. Besides, it will afford unbounded gratification to behold any of these universally admired ornaments of the Green-house improving by our assistance and under our immediate observation. There is nothing to prevent any individual from producing splendid varieties in a few years. Mr. Hogg correctly observes, "It is very probable in a few years we shall have as great a variety of Camellias, as there are of Tulips, Hyacinths, Carnations, Auriculas, &c." It has been often said that these plants are difficult of cultivation. This is unfounded, indeed they are the reverse if put in a soil congenial to their nature. When highly manured soils are given, which are poisonous to the plants, sickness or death will inevitably ensue; but this cannot be attributed to the delicacy of their nature. We can unhesitatingly say there is no Green-house plant more hardy
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    or easier ofcultivation, and they are equally so in the parlour, if not kept confined in a room where there is a continuance of drying fire heat, their constitution not agreeing with an arid atmosphere.
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    Flower-Garden. OCTOBER. OF PLANTING VARIOUSBULBOUS FLOWER ROOTS. From the middle of October to the beginning of November is the best period for a general planting of Dutch bulbs. Cròcuses are the earliest in flower, and may be planted about six inches off the edgings, about four inches apart and two deep, or in beds four feet wide; the varieties selected and planted across the bed in rows of distinct colours, they flowering so early, and in that manner have a grand effect. There are above sixty varieties to be had. Hyacinths. The ground that was prepared for these last month, should be all divided into beds four feet wide, leaving between each alleys of twenty inches. Skim off three inches of the surface of the former into the latter, level the bed smoothly with the rake, and mark it off in rows eight inches apart. Plant the roots in the row eight inches asunder. Thus they will be squares of eight inches, and by planting the different colours alternately the bed will be beautifully diversified. Press each root gently down with the hand, that in covering up they may not be displaced. Put about four inches of earth over the crowns, which will make the beds from two to three inches higher than the alleys. The beds before and after planting should be gently rounded from the middle to each side to let the rain pass off. Finish all by raking evenly, straighten the edgings with the line, and clear out the alleys or pathways. Tulips like a lighter and richer earth than Hyacinths. Prepare the beds in the same manner, and so as the roots will stand nine inches
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    apart each way;cover them five inches deep, as the new bulbs are produced above the old. If it is intended to screen either of these while in flower, the beds should be made wider. Where two beds are to be shaded under one awning, make the alleys alternately two or three feet wide; the one two feet wide to be under the awning. Polyanthus and Italian Narcissus, may be planted in every respect as Hyacinths, only they require a lighter and richer soil. Jonquils. Plant these in the same soil as Tulips, six inches apart, and cover three inches deep. They do not flower so well the first year as in the second and third, therefore should only be lifted every third year. Anemones and Ranunculuses. These roots like a fresh rich, well pulverized, loamy soil. In light sandy soils they will languish in early droughts, and sometimes do not show their flowers fully. Cow manure is the best to use for enriching the soil. The whole should be well mixed and incorporated to the depth of eighteen or twenty inches. The roots may be planted in four-foot beds, or in such a manner as a low frame of boards can be placed over them, when the winter sets in very severe. If intended to be shaded while in flower, leave a sufficiency of space in the alleys as directed for Tulips and Hyacinths. Do not raise the beds above one inch higher than the alleys, and form the surface level, in order to detain rather than throw off moisture. Then draw drills exactly two inches deep and six inches apart across the bed. In these place the roots, claws down, about four inches distant from each other. The roots of the Anemones are flat, and the side on which there are small protuberances, is that from which the stems proceed. Press each root a little down with the hand, and cover all carefully so as not to displace them. Smooth the surface with the rake, leaving the bed quite level. Many other bulbous flowers might be added to the above; but as their culture is so similar, it would be superfluous to say more of
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    them. They shouldbe allowed space and depth according to the size of the bulb; a covering of two inches for the smallest, and five for the largest, will generally answer, and the intermediate roots in proportion. We will enumerate a few of the different kinds, Starch and Musk Hyacinths; of Narcissus, the Paper, Grand Monarque, and Nodding, with the two previously mentioned, are the most profuse in flower. Some of them will have above twelve flowers on one stem. Of Lilies, all the varieties of Mártagon, Tigrìnum and Chalcedónicum, with our native species and varieties. Of Iris, Lusitánica, two varieties, yellow and blue; Xiphioídes, or Ziphioídes; and Pérsica, are the finest of the bulbous sorts. Snow-drop with several other minor bulbs. All of these flowering bulbs may be advantageously planted in patches through the garden by taking out about one square foot of earth. Break it well, and if poor enrich it. Plant four bulbs in each of the same colour, and the clumps that are contiguous to contain different colours. PLANTING AND TRANSPLANTING. This is a very proper period to plant the beautiful and early flowering Pyrus japónica, now called Cydónia japónica. The blossoms are of a rich scarlet colour. It is the earliest flowering shrub of the garden, and deciduous, though said by some to be "an evergreen." The plant is bushy, and well adapted for single plants in grass plats, or forming low ornamental hedges. There is likewise C. j. álba, a fine white variety of the same habit, and both are of the hardiest nature —also for the various species of Anemònes and all the herbaceous Pæonias. Of the latter there are above nineteen species and twenty-two varieties, a few of which are particularly esteemed, and exceedingly handsome. P. èdulis whitlíji is a splendid large double P èdulis white; P. Hùmei is a beautiful large double dark blush; P. èdulis fràgrans is a fine large double scarlet, rose-scented variety. These three plants
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    ought to bein every garden. The flowers are full in the centre, and frequently above six inches in diameter; P. álba chinènsis is said to be the largest and finest of the herbaceous sorts; colour pure white, with pink at the bottom of the petals—it is a scarce variety; P. paradóxa fimbàtria, fringed double red, and esteemed; P. officinális rúbra is the common double red. There are several other very fine single species and varieties, the flowers of which are principally red or blush, but none so magnificent as the above mentioned. This is perhaps a more favourable period to plant Dodecátheon than March; for its character see that month of this department. Asclèpias tuberòsa should now be planted. Double Primroses, Polyanthus, Daisies, &c. Any of these that were planted in shaded situations in spring, and have been preserved through the summer, should have for their farther protection a bed well sheltered from the north west, in which they should be planted four inches apart. Give them a few sprinklings of water in the morning, and have a temporary frame of rough boards put together to place over them during the severity of winter. The frame may be covered with the same in place of glass, which must be kept over them while they are in a frozen state. Any other plants that are in the ground, which are intended to be protected with frames through the winter, ought to be immediately lifted and potted; and treated as directed for all new potted plants. GRASS AND GRAVEL WALKS. The former should be trimly cut and well rolled this month, that they may appear neat all winter. Never allow decayed leaves to lay any time upon them, as they are apt to rot out the grass. The latter should be divested of every weed, and receive a firm rolling. Clear them at all times of leaves and other litter. These, if on a declivity, and have not a firm substantial bottom, will be subject to be cut up with every heavy rain. A break should be put in every twenty, forty,
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    or eighty feet,to throw off the water. A strong plank will answer perfectly well, but in such situations we would prefer grass-walks. PLANTING EVERGREENS. This month is the best period in autumn to plant these shrubs, and where there is a great extent to be planted it would be advisable to do a part of it now; but we give the preference to April, which see for directions. GENERAL OBSERVATIONS. When the plantings of bulbs, &c. are finished, every part of the garden should have a thorough cleaning. All annual flowers will have passed the season of their beauty; therefore, remove the decayed flower stems or haulm, and trim off the borders. Dig all vacant ground, especially that intended to be planted with shrubs in the ensuing spring, which ought to be dug from one to two feet deep. Roses delight in a deep light soil.
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    Rooms. OCTOBER. Have a stageor stages, as described last month, in the situations where they are intended to remain all winter; place the plants on them from the first to the eighth of this month, beginning with the tallest on the top, graduating to the bottom. It is desirable to place flats or saucers under each, to prevent the water from falling to the floor, and the water should be emptied from the flats of all except those of Cálla and Hydrángea. The latter while dormant should be kept only a little moist. Previous to taking in the plants, they should be divested of every decayed leaf, insects, and all contracted dust, having their shoots neatly tied up, and every one in correct order. Every leaf of the Caméllias ought to be sponged, and the plants placed in a cool airy exposure, shaded from the direct rays of the sun. If the flower buds are too crowded, picking off the weakest will preserve the remainder in greater perfection, and prevent them in part from falling off. Do not on any occasion keep them in a room where there is much fire heat, as the flower buds will not expand in an arid atmosphere. See Green-house this month more largely on this subject. OF BULBOUS ROOTS. Those that are intended to flower in glasses, should be placed therein this month and kept in a cool room. After the fibres begin to push a few shoots, the glasses may be taken to the warmest apartments to cause them to flower early. Bring a few from the coldest to the warmest every two weeks, and thus a succession of bloom may be kept up from January to March. Where the roots
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    intended for potsare still out of the ground, the sooner they are planted the better. (See last month for directions.) Cape Bulbs. All that are unplanted and offering to grow, should be put in pots forthwith. Ample directions are given for the planting of these in the two preceding months. Repot Rùbus rosæfòlius, or Bramble-rose. They should have pots one size larger than those they are now in. To make them flower profusely, when done blooming in May, divide them and put only a few stems in one pot, and repot them in this month, as above directed. GENERAL OBSERVATIONS. Any herbaceous plants in the collection ought to be set aside, and the water in part withheld. When the stems and foliage are decayed, the plants may be put in a cool cellar, where they will not be in danger of frost, and be permitted to remain there until they begin to grow; then bring them to the light, and treat as directed for these kinds of plants. Deciduous plants may be treated in a similar manner.
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