The document discusses the link layer and provides an overview of its goals and services including error detection, multiple access protocols, and local area networks. It outlines the topics that will be covered in the chapter including error detection and correction, multiple access protocols like CSMA/CD, addressing in LANs, Ethernet, switches, and VLANs. The slides are being made freely available for educational use provided proper attribution is given.
The document describes Cisco's three-tier network model consisting of core, distribution, and access layers. The core layer contains the largest, fastest routers and acts as the backbone. The distribution layer is located between the core and access layers and defines network policy. The access layer includes switches connected to end devices like computers and printers. The three-tier model provides benefits like improved performance, management, scalability, and redundancy.
IEEE802.1x authentication is an open standard that provides port-based network access control. It defines encapsulation of the Extensible Authentication Protocol (EAP) over IEEE 802 networks to authenticate devices wishing to connect to a LAN or WLAN. Typical authentication involves initialization, initiation via EAP-Request/Response frames, and negotiation of an EAP Method between the supplicant and authentication server until authentication is successful or failed. For devices that do not support 802.1x, MAC bypass can be used to authenticate using the device's MAC address instead.
This document provides an overview of UTP installation, including rough-in procedures and specifications. It discusses items needed for rough-in like plans, materials lists, and tools. Installation specifications cover standards, placement of raceways and cables, labeling, and testing. Diagrams show outlet types, rack layouts, and bends and clearances. Performance parameters like attenuation, crosstalk, and length are also summarized.
Open Shortest Path First (OSPF) is an interior gateway protocol that uses link state routing and the Dijkstra algorithm to calculate the shortest path to destinations within an autonomous system. It elects a Designated Router to generate network link advertisements and assist in database synchronization between routers. Routers run the Shortest Path First algorithm on their link state databases to determine the best routes and populate their routing tables.
The document discusses how the Link Aggregation Control Protocol (LACP) provides a standardized way for systems connected by aggregated links to negotiate the configuration of those links and enable communication. It describes how LACP works, its support on Juniper devices including SRX series firewalls and chassis clusters, and how to configure LACP modes and intervals on both standalone and clustered devices.
PPP is a protocol for point-to-point connections that defines how two devices can establish a link and exchange data. It uses byte stuffing to allow data transparency and defines the format of frames exchanged. PPP uses three protocols - LCP for link establishment and termination, authentication protocols like PAP and CHAP for verifying identities, and NCP like IPCP to encapsulate network layer data for transmission.
The document describes Cisco's three-tier network model consisting of core, distribution, and access layers. The core layer contains the largest, fastest routers and acts as the backbone. The distribution layer is located between the core and access layers and defines network policy. The access layer includes switches connected to end devices like computers and printers. The three-tier model provides benefits like improved performance, management, scalability, and redundancy.
IEEE802.1x authentication is an open standard that provides port-based network access control. It defines encapsulation of the Extensible Authentication Protocol (EAP) over IEEE 802 networks to authenticate devices wishing to connect to a LAN or WLAN. Typical authentication involves initialization, initiation via EAP-Request/Response frames, and negotiation of an EAP Method between the supplicant and authentication server until authentication is successful or failed. For devices that do not support 802.1x, MAC bypass can be used to authenticate using the device's MAC address instead.
This document provides an overview of UTP installation, including rough-in procedures and specifications. It discusses items needed for rough-in like plans, materials lists, and tools. Installation specifications cover standards, placement of raceways and cables, labeling, and testing. Diagrams show outlet types, rack layouts, and bends and clearances. Performance parameters like attenuation, crosstalk, and length are also summarized.
Open Shortest Path First (OSPF) is an interior gateway protocol that uses link state routing and the Dijkstra algorithm to calculate the shortest path to destinations within an autonomous system. It elects a Designated Router to generate network link advertisements and assist in database synchronization between routers. Routers run the Shortest Path First algorithm on their link state databases to determine the best routes and populate their routing tables.
The document discusses how the Link Aggregation Control Protocol (LACP) provides a standardized way for systems connected by aggregated links to negotiate the configuration of those links and enable communication. It describes how LACP works, its support on Juniper devices including SRX series firewalls and chassis clusters, and how to configure LACP modes and intervals on both standalone and clustered devices.
PPP is a protocol for point-to-point connections that defines how two devices can establish a link and exchange data. It uses byte stuffing to allow data transparency and defines the format of frames exchanged. PPP uses three protocols - LCP for link establishment and termination, authentication protocols like PAP and CHAP for verifying identities, and NCP like IPCP to encapsulate network layer data for transmission.
SIP (Session Initiation Protocol) trunking connects a company's PBX to the existing telephone network infrastructure via the internet using VoIP. It was originally designed in 1996 and standardized in 2000. SIP trunking provides benefits like virtual phone numbers, reduced equipment needs, business continuity, and flexible trunk quantities. However, considerations must include system compatibility, additional bandwidth requirements, and challenges like supporting fax/modem traffic and 911 calls. The document discusses ideal environments for SIP trunking like companies with multiple locations, seasonal needs, or those seeking increased functionality. It also reviews cost components and provides an overview of SIP trunking.
This document provides an overview of the TCP/IP protocol stack. It discusses the four layers of TCP/IP - network interface, internet, transport and application layer - and how they relate to the seven-layer OSI model. Key protocols of each TCP/IP layer like IP, TCP, UDP, HTTP, FTP, SMTP are explained along with their functions. Other topics covered include ports, port scanning, and Windows sockets API.
The document provides an overview of IEEE 802.11 standards for wireless local area networks. It discusses the creation of 802.11 by IEEE, the physical layer, frame formats, and various 802.11 protocols including 802.11b, 802.11a, 802.11g, 802.11n, and 802.11ac. It also describes the media access control including CSMA/CA and security features like authentication and WEP encryption.
This document outlines 107 labs for networking fundamentals, including configuration, verification, and troubleshooting of topics like IP addressing, routing protocols, switching, VLANs, ACLs, NAT, DHCP, SNMP, device security, wireless access points, and more. Each lab has a section for configuration and verification. The document provides a table of contents to help navigate the various sections and labs.
The document discusses the protocol layers and architecture of IEEE 802.11 wireless LAN standards. It describes the functions of the physical, medium access control (MAC), and logical link control (LLC) layers. The MAC frame format and access control methods using interframe spaces are also summarized. Additionally, it outlines services provided within IEEE 802.11 wireless distributions systems including distribution, integration, and mobility-related services.
Design, Deployment and Management of Unified WLANCisco Canada
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1) 1st and 2nd generation WLAN architectures placed client traffic on local VLANs on the access point, while 3rd generation architectures use a controller to bridge client traffic centrally.
2) CAPWAP is used between access points and WLAN controllers to carry both control and data traffic, with the control plane encrypted using DTLS and data encryption being optional.
3) CAPWAP supports two operation modes - split MAC which centralizes processing on the controller, and local MAC (FlexConnect) which bridges traffic locally on the access point. Cisco recommends deterministic redundancy over dynamic for better control and fallback options.
IP addresses are a unique identifier for devices connected to a network. They allow for the delivery of data packets across networks. The structure of IP addresses includes a network prefix that identifies the network and a host number that identifies the specific device. Techniques like subnetting, CIDR, and IPv6 were developed to address the limited available IPv4 address space and allow for more efficient allocation and routing of IP addresses.
Design and Deployment of Enterprise Wirlesss NetworksCisco Mobility
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This document discusses Cisco's controller-based wireless LAN architecture and mobility features. It covers:
1) The controller-based architecture uses wireless LAN controllers and access points to centralize management and control of wireless clients. Controllers handle client authentication, security, mobility, and network access across multiple access points.
2) Mobility is enabled through mobility groups, which allow controllers to peer with each other and exchange information to support seamless roaming across controller boundaries.
3) Cisco's technologies like CAPWAP, split MAC, and static IP mobility aim to make wireless roaming fast and seamless while maintaining security as clients move between access points and across subnets.
This document provides an overview of Deep Packet Inspection (DPI) technology and Sandvine's DPI solution. It describes key components of Sandvine's solution including the Policy Traffic Switch (PTS) for real-time traffic policy enforcement, the Policy Broker (SPB) for subscriber and policy configuration, and the Service Delivery Engine (SDE) for control plane policy enforcement. It also provides examples of configuration for the PTS and SPB. Finally, it introduces Sand Script, the language used for policy rule configuration in Sandvine's solution.
VLANs logically segment LANs into broadcast domains by using switches to assign ports and their attached devices to VLAN groups based on their MAC address, IP subnet, or switch port. This allows devices that are physically located on different floors or buildings to belong to the same logical LAN segment while preventing Layer 2 broadcasts from crossing VLAN boundaries. VLAN trunk links between switches allow multiple VLANs to be transmitted over the same physical link.
Repeaters are electronic devices that regenerate signals to extend the range of a local area network (LAN) by connecting two segments. They work at the physical layer of the OSI model by receiving signals, regenerating the original bit pattern, and forwarding the refreshed signal without any filtering or intelligent functions. Repeaters must be placed between segments before the signal becomes too weak or corrupted to extend the physical length and increase the range of a LAN.
This document discusses OSPF packet types used for communication between routers to discover network routes, add link state entries to maintain routing information using LSA sequence numbers which can be viewed using the show IP OSPF database command, and debugged in more detail using the debug ip OSPF packets command.
in the slide we discuss - VLAN overview, effectiveness, benefits, how VLAN work, memberships mode, operations, creation Guidelines, add VLAN, accessing,managing and verifying .
This document provides an overview of local area networks (LANs) and their components. It discusses the different types of computer networks and LAN topologies. It also describes some key LAN devices like hubs, switches, routers, wireless access points, and network interface cards. It provides an introduction to the TCP/IP networking protocols and the IEEE 802.11 wireless networking standards.
The document discusses IPv6 addressing and summarizes:
- IPv6 addresses are 128-bit hexadecimal addresses consisting of 8 sections separated by colons, with the first 3 sections making up the prefix or network portion and the last 4 sections being the interface ID.
- Addressing hierarchies are defined, with the first bits identifying the registry and subsequent bits identifying the ISP and site.
- Methods for compressing zeros, representing loopback addresses, and defining link-local and multicast addresses are covered.
- IPv6 enhances IPv4 by allowing larger addresses and more efficient routing while introducing features like built-in encryption.
VLAN Trunking Protocol (VTP) is a Cisco proprietary protocol that propagates the definition of Virtual
Local Area Networks (VLAN) on the whole local area network.[1] To do this, VTP carries VLAN
information to all the switches in a VTP domain. VTP advertisements can be sent over ISL, 802.1Q, IEEE
802.10 and LANE trunks. VTP is available on most of the Cisco Catalyst Family products.
BGP is the exterior gateway protocol that connects different autonomous systems on the internet. It allows for the exchange of routing and reachability information between these systems. BGP operates using a finite state machine to manage the states of connections between peers. It establishes TCP connections between routers to exchange routing updates and keep connections alive through regular keepalive messages. BGP version 4, defined in RFC 4271, is the current standard implementation which supports features like classless inter-domain routing and route aggregation.
The document discusses the link layer and provides an overview of its services and functions. It describes multiple access protocols for shared mediums including ALOHA, slotted ALOHA, CSMA, CSMA/CD. CSMA/CD is used in Ethernet and detects collisions to reduce wasted bandwidth. The document outlines error detection methods like parity checking, cyclic redundancy checks, and discusses how the link layer is implemented in network interface cards.
This document discusses the link layer and provides an overview of its services and context. It describes how the link layer is implemented in network interface cards and how these cards encapsulate datagrams into frames. It also outlines the topics to be covered, including error detection and correction, multiple access protocols, local area networks, and link virtualization.
SIP (Session Initiation Protocol) trunking connects a company's PBX to the existing telephone network infrastructure via the internet using VoIP. It was originally designed in 1996 and standardized in 2000. SIP trunking provides benefits like virtual phone numbers, reduced equipment needs, business continuity, and flexible trunk quantities. However, considerations must include system compatibility, additional bandwidth requirements, and challenges like supporting fax/modem traffic and 911 calls. The document discusses ideal environments for SIP trunking like companies with multiple locations, seasonal needs, or those seeking increased functionality. It also reviews cost components and provides an overview of SIP trunking.
This document provides an overview of the TCP/IP protocol stack. It discusses the four layers of TCP/IP - network interface, internet, transport and application layer - and how they relate to the seven-layer OSI model. Key protocols of each TCP/IP layer like IP, TCP, UDP, HTTP, FTP, SMTP are explained along with their functions. Other topics covered include ports, port scanning, and Windows sockets API.
The document provides an overview of IEEE 802.11 standards for wireless local area networks. It discusses the creation of 802.11 by IEEE, the physical layer, frame formats, and various 802.11 protocols including 802.11b, 802.11a, 802.11g, 802.11n, and 802.11ac. It also describes the media access control including CSMA/CA and security features like authentication and WEP encryption.
This document outlines 107 labs for networking fundamentals, including configuration, verification, and troubleshooting of topics like IP addressing, routing protocols, switching, VLANs, ACLs, NAT, DHCP, SNMP, device security, wireless access points, and more. Each lab has a section for configuration and verification. The document provides a table of contents to help navigate the various sections and labs.
The document discusses the protocol layers and architecture of IEEE 802.11 wireless LAN standards. It describes the functions of the physical, medium access control (MAC), and logical link control (LLC) layers. The MAC frame format and access control methods using interframe spaces are also summarized. Additionally, it outlines services provided within IEEE 802.11 wireless distributions systems including distribution, integration, and mobility-related services.
Design, Deployment and Management of Unified WLANCisco Canada
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1) 1st and 2nd generation WLAN architectures placed client traffic on local VLANs on the access point, while 3rd generation architectures use a controller to bridge client traffic centrally.
2) CAPWAP is used between access points and WLAN controllers to carry both control and data traffic, with the control plane encrypted using DTLS and data encryption being optional.
3) CAPWAP supports two operation modes - split MAC which centralizes processing on the controller, and local MAC (FlexConnect) which bridges traffic locally on the access point. Cisco recommends deterministic redundancy over dynamic for better control and fallback options.
IP addresses are a unique identifier for devices connected to a network. They allow for the delivery of data packets across networks. The structure of IP addresses includes a network prefix that identifies the network and a host number that identifies the specific device. Techniques like subnetting, CIDR, and IPv6 were developed to address the limited available IPv4 address space and allow for more efficient allocation and routing of IP addresses.
Design and Deployment of Enterprise Wirlesss NetworksCisco Mobility
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This document discusses Cisco's controller-based wireless LAN architecture and mobility features. It covers:
1) The controller-based architecture uses wireless LAN controllers and access points to centralize management and control of wireless clients. Controllers handle client authentication, security, mobility, and network access across multiple access points.
2) Mobility is enabled through mobility groups, which allow controllers to peer with each other and exchange information to support seamless roaming across controller boundaries.
3) Cisco's technologies like CAPWAP, split MAC, and static IP mobility aim to make wireless roaming fast and seamless while maintaining security as clients move between access points and across subnets.
This document provides an overview of Deep Packet Inspection (DPI) technology and Sandvine's DPI solution. It describes key components of Sandvine's solution including the Policy Traffic Switch (PTS) for real-time traffic policy enforcement, the Policy Broker (SPB) for subscriber and policy configuration, and the Service Delivery Engine (SDE) for control plane policy enforcement. It also provides examples of configuration for the PTS and SPB. Finally, it introduces Sand Script, the language used for policy rule configuration in Sandvine's solution.
VLANs logically segment LANs into broadcast domains by using switches to assign ports and their attached devices to VLAN groups based on their MAC address, IP subnet, or switch port. This allows devices that are physically located on different floors or buildings to belong to the same logical LAN segment while preventing Layer 2 broadcasts from crossing VLAN boundaries. VLAN trunk links between switches allow multiple VLANs to be transmitted over the same physical link.
Repeaters are electronic devices that regenerate signals to extend the range of a local area network (LAN) by connecting two segments. They work at the physical layer of the OSI model by receiving signals, regenerating the original bit pattern, and forwarding the refreshed signal without any filtering or intelligent functions. Repeaters must be placed between segments before the signal becomes too weak or corrupted to extend the physical length and increase the range of a LAN.
This document discusses OSPF packet types used for communication between routers to discover network routes, add link state entries to maintain routing information using LSA sequence numbers which can be viewed using the show IP OSPF database command, and debugged in more detail using the debug ip OSPF packets command.
in the slide we discuss - VLAN overview, effectiveness, benefits, how VLAN work, memberships mode, operations, creation Guidelines, add VLAN, accessing,managing and verifying .
This document provides an overview of local area networks (LANs) and their components. It discusses the different types of computer networks and LAN topologies. It also describes some key LAN devices like hubs, switches, routers, wireless access points, and network interface cards. It provides an introduction to the TCP/IP networking protocols and the IEEE 802.11 wireless networking standards.
The document discusses IPv6 addressing and summarizes:
- IPv6 addresses are 128-bit hexadecimal addresses consisting of 8 sections separated by colons, with the first 3 sections making up the prefix or network portion and the last 4 sections being the interface ID.
- Addressing hierarchies are defined, with the first bits identifying the registry and subsequent bits identifying the ISP and site.
- Methods for compressing zeros, representing loopback addresses, and defining link-local and multicast addresses are covered.
- IPv6 enhances IPv4 by allowing larger addresses and more efficient routing while introducing features like built-in encryption.
VLAN Trunking Protocol (VTP) is a Cisco proprietary protocol that propagates the definition of Virtual
Local Area Networks (VLAN) on the whole local area network.[1] To do this, VTP carries VLAN
information to all the switches in a VTP domain. VTP advertisements can be sent over ISL, 802.1Q, IEEE
802.10 and LANE trunks. VTP is available on most of the Cisco Catalyst Family products.
BGP is the exterior gateway protocol that connects different autonomous systems on the internet. It allows for the exchange of routing and reachability information between these systems. BGP operates using a finite state machine to manage the states of connections between peers. It establishes TCP connections between routers to exchange routing updates and keep connections alive through regular keepalive messages. BGP version 4, defined in RFC 4271, is the current standard implementation which supports features like classless inter-domain routing and route aggregation.
The document discusses the link layer and provides an overview of its services and functions. It describes multiple access protocols for shared mediums including ALOHA, slotted ALOHA, CSMA, CSMA/CD. CSMA/CD is used in Ethernet and detects collisions to reduce wasted bandwidth. The document outlines error detection methods like parity checking, cyclic redundancy checks, and discusses how the link layer is implemented in network interface cards.
This document discusses the link layer and provides an overview of its services and context. It describes how the link layer is implemented in network interface cards and how these cards encapsulate datagrams into frames. It also outlines the topics to be covered, including error detection and correction, multiple access protocols, local area networks, and link virtualization.
The document discusses link layer protocols and multiple access protocols. It provides examples of channel partitioning protocols like TDMA and FDMA that divide the channel into time slots or frequency bands. It also discusses random access protocols like ALOHA, slotted ALOHA, and CSMA/CD that do not partition the channel and can result in collisions. CSMA/CD improves on CSMA by allowing nodes to detect collisions and abort transmissions to reduce wasted bandwidth. "Taking turns" protocols like polling and token passing allocate channel access by turning to control which node can transmit.
The document provides an overview of the link layer. It discusses the goals and services of the link layer, including error detection, correction, and sharing access to broadcast channels through multiple access protocols. It describes various link layer technologies like Ethernet, switches, and VLANs. It also covers topics like link layer addressing using MAC addresses, the Address Resolution Protocol (ARP) for mapping IP addresses to MAC addresses, and examples of multiple access protocols including Carrier Sense Multiple Access with Collision Detection (CSMA/CD) used in Ethernet networks.
The document discusses data link layer protocols and multiple access protocols. It describes several protocols for sharing a broadcast channel, including slotted ALOHA, CSMA, CSMA/CD, and token passing. It also discusses error detection techniques like parity checking and cyclic redundancy checks used at the data link layer. The goal of the data link layer is to reliably transfer data frames between adjacent nodes over a link using addressing, error detection, flow control and other services.
This document provides an overview and summary of a chapter on link layers and local area networks (LANs) from the textbook "Computer Networking: A Top-Down Approach". It discusses the goals of understanding link layer services and technologies. It also provides an outline of the chapter topics which include error detection and correction, multiple access protocols, LAN addressing, Ethernet, switches, and virtual LANs. The document is intended for educational use and free modification with attribution required.
This document provides an overview and outline of topics to be covered in a chapter about the link layer and local area networks (LANs). It discusses the goals of understanding link layer services like error detection and correction as well as sharing bandwidth on a broadcast channel. It also outlines the key sections to be covered, including multiple access protocols, LAN addressing, Ethernet, switches, and virtual LANs. Sample slides are provided on topics like link layer services, error detection techniques, and multiple access protocols. The document is intended for educational use and asks that the source be cited if used for teaching.
Data centers architecture and design guideMattPeci
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Data center architecture, as an architectural design that establishes connections between switches and servers, is typically created during the data center design and construction phases
This document discusses data center network architectures. It begins by noting that data centers contain tens to hundreds of thousands of closely coupled hosts in close proximity, posing challenges around load management and avoiding bottlenecks. It then describes common data center network components like server racks, top-of-rack switches, core switches, and load balancers. Load balancers direct external client requests and hide the internal data center structure. The network uses a rich interconnection of switches and racks for increased throughput and redundancy. Broad questions are raised around networking massive numbers of machines, virtualization resource management, and reducing operational costs like power.
Lecture 25 Link Layer - Error detection and Multiple Access.pptxHanzlaNaveed1
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The document discusses principles of link layer services including error detection, correction, and sharing a broadcast channel through multiple access protocols. It provides an overview of topics like link layer addressing, local area networks including Ethernet and VLANs. Specific link layer services covered are error detection using techniques like parity checking and cyclic redundancy check (CRC). The document also distinguishes between point-to-point and broadcast links, and describes multiple access protocols for shared broadcast channels including TDMA, FDMA, and random access protocols like slotted ALOHA and CSMA.
This document discusses the link layer and local area networks. It begins with an introduction to link layer services including framing, link access, reliable delivery, flow control, and error detection and correction. It then covers topics like multiple access protocols, including random access protocols like ALOHA and CSMA, and controlled access protocols. Local area network technologies are discussed next, focusing on Ethernet, switches, and addressing protocols like ARP. The document concludes with sections on link virtualization using MPLS and data center networking.
The document discusses the link layer and its services. It introduces key link layer concepts like framing, link access, error detection, flow control, and multiple access protocols. It describes different types of multiple access protocols including channel partitioning protocols like TDMA and FDMA as well as random access protocols like ALOHA and CSMA. It also discusses error detection techniques like parity checking, checksums, and cyclic redundancy checks (CRCs). The document provides examples and comparisons of protocols to convey their tradeoffs and how they address the challenges of sharing communication channels.
Chapter_6_v8.2.pptx osi model powerpointjunkmailus22
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This document provides an overview of a chapter from the textbook "Computer Networking: A Top-Down Approach" by Jim Kurose and Keith Ross. It discusses the use of PowerPoint slides from the textbook and asks that users cite the source if using the slides and note any copyrighted material. The document contains brief summaries of several slides covering topics in the chapter on the link layer and local area networks, including error detection techniques like parity checking and cyclic redundancy checks, and multiple access protocols like TDMA.
The document summarizes key concepts about the data link layer. It discusses the goals and services of the data link layer, including error detection and correction, sharing broadcast channels through multiple access protocols, link layer addressing, and reliable data transfer and flow control. It also provides an overview of common link layer technologies and implementation through instantiation of various data link layer protocols.
The document summarizes Chapter 5 of the textbook "Computer Networking: A Top Down Approach" which covers the link layer. It discusses the goals and outline of the chapter, including understanding link layer services like error detection and correction. It then covers various topics within the link layer such as error detection techniques, multiple access protocols for shared mediums, and examples like Ethernet, switches, and VLANs.
Medium Access PROTOCOL b yENGR. FAWAD KHAN UET BANNU KP PAKISTANirfan sami
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1. The document discusses medium access control (MAC) protocols for shared broadcast links at the link layer. It covers three main classes of MAC protocols: channel partitioning, random access, and "taking turns" protocols.
2. Channel partitioning protocols like TDMA and FDMA divide the channel into time or frequency slots and allocate slots to nodes. Random access protocols like ALOHA, CSMA, and CSMA/CD allow nodes to transmit randomly and include mechanisms to detect and handle collisions. "Taking turns" protocols such as polling and token passing coordinate channel access by having nodes take turns transmitting.
3. The ideal MAC protocol allows single or multiple nodes to transmit at the maximum channel rate, is fully decentralized, requires
The document provides an overview of the data link layer and link layer technologies. It begins with an introduction to data link layer services such as framing, error detection, multiple access, and addressing. It then discusses various error detection and correction techniques as well as multiple access protocols including TDMA, FDMA, and random access protocols like ALOHA, slotted ALOHA, and CSMA. The document aims to help readers understand the principles behind data link layer services and different link layer technologies.
The document discusses link layer concepts including link layer addressing, MAC addresses, ARP, Ethernet frames, CSMA/CD, hubs, and switches. It explains that MAC addresses are used to deliver frames within a local area network, while IP addresses are used between networks. ARP is used to map IP addresses to MAC addresses on the same network. Ethernet uses CSMA/CD for media access and frames include source and destination MAC addresses. Hubs operate at the physical layer while switches operate at the data link layer and can reduce collisions by isolating segments.
The Department of Veteran Affairs (VA) invited Taylor Paschal, Knowledge & Information Management Consultant at Enterprise Knowledge, to speak at a Knowledge Management Lunch and Learn hosted on June 12, 2024. All Office of Administration staff were invited to attend and received professional development credit for participating in the voluntary event.
The objectives of the Lunch and Learn presentation were to:
- Review what KM âisâ and âisnâtâ
- Understand the value of KM and the benefits of engaging
- Define and reflect on your âwhatâs in it for me?â
- Share actionable ways you can participate in Knowledge - - Capture & Transfer
How information systems are built or acquired puts information, which is what they should be about, in a secondary place. Our language adapted accordingly, and we no longer talk about information systems but applications. Applications evolved in a way to break data into diverse fragments, tightly coupled with applications and expensive to integrate. The result is technical debt, which is re-paid by taking even bigger "loans", resulting in an ever-increasing technical debt. Software engineering and procurement practices work in sync with market forces to maintain this trend. This talk demonstrates how natural this situation is. The question is: can something be done to reverse the trend?
"NATO Hackathon Winner: AI-Powered Drug Search", Taras KlobaFwdays
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This is a session that details how PostgreSQL's features and Azure AI Services can be effectively used to significantly enhance the search functionality in any application.
In this session, we'll share insights on how we used PostgreSQL to facilitate precise searches across multiple fields in our mobile application. The techniques include using LIKE and ILIKE operators and integrating a trigram-based search to handle potential misspellings, thereby increasing the search accuracy.
We'll also discuss how the azure_ai extension on PostgreSQL databases in Azure and Azure AI Services were utilized to create vectors from user input, a feature beneficial when users wish to find specific items based on text prompts. While our application's case study involves a drug search, the techniques and principles shared in this session can be adapted to improve search functionality in a wide range of applications. Join us to learn how PostgreSQL and Azure AI can be harnessed to enhance your application's search capability.
Discover top-tier mobile app development services, offering innovative solutions for iOS and Android. Enhance your business with custom, user-friendly mobile applications.
High performance Serverless Java on AWS- GoTo Amsterdam 2024Vadym Kazulkin
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Java is for many years one of the most popular programming languages, but it used to have hard times in the Serverless community. Java is known for its high cold start times and high memory footprint, comparing to other programming languages like Node.js and Python. In this talk I'll look at the general best practices and techniques we can use to decrease memory consumption, cold start times for Java Serverless development on AWS including GraalVM (Native Image) and AWS own offering SnapStart based on Firecracker microVM snapshot and restore and CRaC (Coordinated Restore at Checkpoint) runtime hooks. I'll also provide a lot of benchmarking on Lambda functions trying out various deployment package sizes, Lambda memory settings, Java compilation options and HTTP (a)synchronous clients and measure their impact on cold and warm start times.
The Microsoft 365 Migration Tutorial For Beginner.pptxoperationspcvita
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This presentation will help you understand the power of Microsoft 365. However, we have mentioned every productivity app included in Office 365. Additionally, we have suggested the migration situation related to Office 365 and how we can help you.
You can also read: https://www.systoolsgroup.com/updates/office-365-tenant-to-tenant-migration-step-by-step-complete-guide/
"Scaling RAG Applications to serve millions of users", Kevin GoedeckeFwdays
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How we managed to grow and scale a RAG application from zero to thousands of users in 7 months. Lessons from technical challenges around managing high load for LLMs, RAGs and Vector databases.
Connector Corner: Seamlessly power UiPath Apps, GenAI with prebuilt connectorsDianaGray10
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Join us to learn how UiPath Apps can directly and easily interact with prebuilt connectors via Integration Service--including Salesforce, ServiceNow, Open GenAI, and more.
The best part is you can achieve this without building a custom workflow! Say goodbye to the hassle of using separate automations to call APIs. By seamlessly integrating within App Studio, you can now easily streamline your workflow, while gaining direct access to our Connector Catalog of popular applications.
Weâll discuss and demo the benefits of UiPath Apps and connectors including:
Creating a compelling user experience for any software, without the limitations of APIs.
Accelerating the app creation process, saving time and effort
Enjoying high-performance CRUD (create, read, update, delete) operations, for
seamless data management.
Speakers:
Russell Alfeche, Technology Leader, RPA at qBotic and UiPath MVP
Charlie Greenberg, host
Main news related to the CCS TSI 2023 (2023/1695)Jakub Marek
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An English đŦđ§ translation of a presentation to the speech I gave about the main changes brought by CCS TSI 2023 at the biggest Czech conference on Communications and signalling systems on Railways, which was held in Clarion Hotel Olomouc from 7th to 9th November 2023 (konferenceszt.cz). Attended by around 500 participants and 200 on-line followers.
The original Czech đ¨đŋ version of the presentation can be found here: https://www.slideshare.net/slideshow/hlavni-novinky-souvisejici-s-ccs-tsi-2023-2023-1695/269688092 .
The videorecording (in Czech) from the presentation is available here: https://youtu.be/WzjJWm4IyPk?si=SImb06tuXGb30BEH .
"$10 thousand per minute of downtime: architecture, queues, streaming and fin...Fwdays
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Direct losses from downtime in 1 minute = $5-$10 thousand dollars. Reputation is priceless.
As part of the talk, we will consider the architectural strategies necessary for the development of highly loaded fintech solutions. We will focus on using queues and streaming to efficiently work and manage large amounts of data in real-time and to minimize latency.
We will focus special attention on the architectural patterns used in the design of the fintech system, microservices and event-driven architecture, which ensure scalability, fault tolerance, and consistency of the entire system.
inQuba Webinar Mastering Customer Journey Management with Dr Graham HillLizaNolte
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Chapter_5_CN Link Layer.ppt
1. Chapter 5
Link Layer
Computer
Networking: A
Top Down
Approach
6th edition
Jim Kurose, Keith Ross
Addison-Wesley
March 2012
A note on the use of these ppt slides:
Weâre making these slides freely available to all (faculty, students, readers).
Theyâre in PowerPoint form so you see the animations; and can add, modify,
and delete slides (including this one) and slide content to suit your needs.
They obviously represent a lot of work on our part. In return for use, we only
ask the following:
īļ If you use these slides (e.g., in a class) that you mention their source
(after all, weâd like people to use our book!)
īļ If you post any slides on a www site, that you note that they are adapted
from (or perhaps identical to) our slides, and note our copyright of this
material.
Thanks and enjoy! JFK/KWR
All material copyright 1996-2012
J.F Kurose and K.W. Ross, All Rights Reserved
Link Layer 5-1
2. Link Layer 5-2
Chapter 5: Link layer
our goals:
īļ understand principles behind link layer
services:
ī§ error detection, correction
ī§ sharing a broadcast channel: multiple access
ī§ link layer addressing
ī§ local area networks: Ethernet, VLANs
īļ instantiation, implementation of various
link layer technologies
3. Link Layer 5-3
Link layer, LANs: outline
5.1 introduction,
services
5.2 error detection,
correction
5.3 multiple access
protocols
5.4 LANs
ī§ addressing, ARP
ī§ Ethernet
ī§ switches
ī§ VLANS
5.5 link virtualization:
MPLS
5.6 data center
networking
5.7 a day in the life of a
web request
4. Link Layer 5-4
Link layer: introduction
terminology:
īļ hosts and routers: nodes
īļ communication channels
that connect adjacent
nodes along
communication path: links
ī§ wired links
ī§ wireless links
ī§ LANs
īļ layer-2 packet: frame,
encapsulates datagram
data-link layer has responsibility of
transferring datagram from one node
to physically adjacent node over a link
global ISP
5. Link Layer 5-5
Link layer: context
īļ datagram transferred by
different link protocols
over different links:
ī§ e.g., Ethernet on first
link, frame relay on
intermediate links,
802.11 on last link
īļ each link protocol
provides different services
ī§ e.g., may or may not
provide rdt over link
transportation analogy:
īļ trip from Princeton to Lausanne
ī§ limo: Princeton to JFK
ī§ plane: JFK to Geneva
ī§ train: Geneva to Lausanne
īļ tourist = datagram
īļ transport segment =
communication link
īļ transportation mode = link
layer protocol
īļ travel agent = routing
algorithm
6. Link Layer 5-6
Link layer services
īļ framing, link access:
ī§ encapsulate datagram into frame, adding header,
trailer
ī§ channel access if shared medium
ī§ âMACâ addresses used in frame headers to
identify source, dest
âĸ different from IP address!
īļ reliable delivery between adjacent nodes
ī§ we learned how to do this already (chapter 3)!
ī§ seldom used on low bit-error link (fiber, some
twisted pair)
ī§ wireless links: high error rates
âĸ Q: why both link-level and end-end reliability?
7. Link Layer 5-7
īļ flow control:
ī§ pacing between adjacent sending and receiving nodes
īļ error detection:
ī§ errors caused by signal attenuation, noise.
ī§ receiver detects presence of errors:
âĸ signals sender for retransmission or drops frame
īļ error correction:
ī§ receiver identifies and corrects bit error(s) without resorting
to retransmission
īļ half-duplex and full-duplex
ī§ with half duplex, nodes at both ends of link can transmit, but
not at same time
Link layer services
(more)
8. Link Layer 5-8
Where is the link layer
implemented?
īļ in each and every host
īļ link layer implemented in
âadaptorâ (aka network
interface card NIC) or on
a chip
ī§ Ethernet card, 802.11
card; Ethernet chipset
ī§ implements link,
physical layer
īļ attaches into hostâs
system buses
īļ combination of hardware,
software, firmware
controller
physical
transmission
cpu memory
host
bus
(e.g., PCI)
network adapter
card
application
transport
network
link
link
physical
9. Link Layer 5-9
Adaptors communicating
īļ sending side:
ī§ encapsulates
datagram in frame
ī§ adds error checking
bits, rdt, flow control,
etc.
īļ receiving side
ī§ looks for errors, rdt,
flow control, etc
ī§ extracts datagram,
passes to upper layer
at receiving side
controller controller
sending host receiving host
datagram datagram
datagram
frame
10. Link Layer 5-10
Link layer, LANs: outline
5.1 introduction,
services
5.2 error detection,
correction
5.3 multiple access
protocols
5.4 LANs
ī§ addressing, ARP
ī§ Ethernet
ī§ switches
ī§ VLANS
5.5 link virtualization:
MPLS
5.6 data center
networking
5.7 a day in the life of a
web request
11. Link Layer 5-11
Error detection
EDC= Error Detection and Correction bits (redundancy)
D = Data protected by error checking, may include header fields
âĸ Error detection not 100% reliable!
âĸ protocol may miss some errors, but rarely
âĸ larger EDC field yields better detection and correction
otherwise
12. Link Layer 5-12
Parity checking
single bit parity:
īļ detect single bit
errors
two-dimensional bit parity:
īļ detect and correct single bit errors
0 0
13. Link Layer 5-13
Internet checksum (review)
sender:
īļ treat segment contents
as sequence of 16-bit
integers
īļ checksum: addition
(1âs complement sum)
of segment contents
īļ sender puts checksum
value into UDP
checksum field
receiver:
īļ compute checksum of
received segment
īļ check if computed
checksum equals
checksum field value:
ī§ NO - error detected
ī§ YES - no error
detected. But maybe
errors nonetheless?
goal: detect âerrorsâ (e.g., flipped bits) in transmitted
packet (note: used at transport layer only)
14. Link Layer 5-14
Cyclic redundancy check
īļ more powerful error-detection coding
īļ view data bits, D, as a binary number
īļ choose r+1 bit pattern (generator), G
īļ goal: choose r CRC bits, R, such that
ī§ <D,R> exactly divisible by G (modulo 2)
ī§ receiver knows G, divides <D,R> by G. If non-zero
remainder: error detected!
ī§ can detect all burst errors less than r+1 bits
īļ widely used in practice (Ethernet, 802.11 WiFi, ATM)
15. Link Layer 5-15
CRC example
want:
D.2r XOR R = nG
equivalently:
D.2r = nG XOR R
equivalently:
if we divide D.2r by
G, want remainder
R to satisfy:
R = remainder[ ]
D.2r
G
16. Link Layer 5-16
Link layer, LANs: outline
5.1 introduction,
services
5.2 error detection,
correction
5.3 multiple access
protocols
5.4 LANs
ī§ addressing, ARP
ī§ Ethernet
ī§ switches
ī§ VLANS
5.5 link virtualization:
MPLS
5.6 data center
networking
5.7 a day in the life of a
web request
17. Link Layer 5-17
Multiple access links, protocols
two types of âlinksâ:
īļ point-to-point
ī§ PPP for dial-up access
ī§ point-to-point link between Ethernet switch, host
īļ broadcast (shared wire or medium)
ī§ old-fashioned Ethernet
ī§ upstream HFC
ī§ 802.11 wireless LAN
shared wire (e.g.,
cabled Ethernet)
shared RF
(e.g., 802.11 WiFi)
shared RF
(satellite)
humans at a
cocktail party
(shared air, acoustical)
18. Link Layer 5-18
Multiple access protocols
īļ single shared broadcast channel
īļ two or more simultaneous transmissions by nodes:
interference
ī§ collision if node receives two or more signals at the
same time
multiple access protocol
īļ distributed algorithm that determines how nodes share
channel, i.e., determine when node can transmit
īļ communication about channel sharing must use channel
itself!
ī§ no out-of-band channel for coordination
19. Link Layer 5-19
An ideal multiple access protocol
given: broadcast channel of rate R bps
desiderata:
1. when one node wants to transmit, it can send at rate
R.
2. when M nodes want to transmit, each can send at
average rate R/M
3. fully decentralized:
âĸ no special node to coordinate transmissions
âĸ no synchronization of clocks, slots
4. simple
20. Link Layer 5-20
MAC protocols: taxonomy
three broad classes:
īļ channel partitioning
ī§ divide channel into smaller âpiecesâ (time slots, frequency,
code)
ī§ allocate piece to node for exclusive use
īļ random access
ī§ channel not divided, allow collisions
ī§ ârecoverâ from collisions
īļ âtaking turnsâ
ī§ nodes take turns, but nodes with more to send can take
longer turns
21. Link Layer 5-21
Channel partitioning MAC protocols:
TDMA
TDMA: time division multiple access
īļ access to channel in "rounds"
īļ each station gets fixed length slot (length =
pkt trans time) in each round
īļ unused slots go idle
īļ example: 6-station LAN, 1,3,4 have pkt, slots
2,5,6 idle
1 3 4 1 3 4
6-slot
frame
6-slot
frame
22. Link Layer 5-22
FDMA: frequency division multiple access
īļ channel spectrum divided into frequency bands
īļ each station assigned fixed frequency band
īļ unused transmission time in frequency bands go idle
īļ example: 6-station LAN, 1,3,4 have pkt, frequency bands
2,5,6 idle
frequency
bands
FDM cable
Channel partitioning MAC protocols:
FDMA
23. Link Layer 5-23
Random access protocols
īļ when node has packet to send
ī§ transmit at full channel data rate R.
ī§ no a priori coordination among nodes
īļ two or more transmitting nodes â âcollisionâ,
īļ random access MAC protocol specifies:
ī§ how to detect collisions
ī§ how to recover from collisions (e.g., via delayed
retransmissions)
īļ examples of random access MAC protocols:
ī§ slotted ALOHA
ī§ ALOHA
ī§ CSMA, CSMA/CD, CSMA/CA
24. Link Layer 5-24
Slotted ALOHA
assumptions:
īļ all frames same size
īļ time divided into equal
size slots (time to
transmit 1 frame)
īļ nodes start to transmit
only slot beginning
īļ nodes are synchronized
īļ if 2 or more nodes
transmit in slot, all nodes
detect collision
operation:
īļ when node obtains fresh
frame, transmits in next slot
ī§ if no collision: node can
send new frame in next
slot
ī§ if collision: node
retransmits frame in
each subsequent slot
with prob. p until
success
25. Link Layer 5-25
Pros:
īļ single active node can
continuously transmit at
full rate of channel
īļ highly decentralized:
only slots in nodes need
to be in sync
īļ simple
Cons:
īļ collisions, wasting slots
īļ idle slots
īļ nodes may be able to
detect collision in less
than time to transmit
packet
īļ clock synchronization
Slotted ALOHA
1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C C
S S S
E E E
26. Link Layer 5-26
īļ suppose: N nodes with
many frames to send,
each transmits in slot
with probability p
īļ prob that given node
has success in a slot =
p(1-p)N-1
īļ prob that any node has
a success = Np(1-p)N-1
īļ max efficiency: find p*
that maximizes
Np(1-p)N-1
īļ for many nodes, take
limit of Np*(1-p*)N-1 as N
goes to infinity, gives:
max efficiency = 1/e =
.37
efficiency: long-run
fraction of successful
slots
(many nodes, all with
many frames to send)
at best: channel
used for useful
transmissions
37%
of time!
!
Slotted ALOHA: efficiency
27. Link Layer 5-27
Pure (unslotted) ALOHA
īļ unslotted Aloha: simpler, no synchronization
īļ when frame first arrives
ī§ transmit immediately
īļ collision probability increases:
ī§ frame sent at t0 collides with other frames sent in [t0-
1,t0+1]
28. Link Layer 5-28
Pure ALOHA efficiency
P(success by given node) = P(node transmits) .
P(no other node transmits in [t0-1,t0] .
P(no other node transmits in [t0-1,t0]
= p . (1-p)N-1 . (1-p)N-1
= p . (1-p)2(N-1)
âĻ choosing optimum p and then letting n
= 1/(2e) = .18
even worse than slotted Aloha!
29. Link Layer 5-29
CSMA (carrier sense multiple
access)
CSMA: listen before transmit:
if channel sensed idle: transmit entire frame
īļ if channel sensed busy, defer transmission
īļ human analogy: donât interrupt others!
30. Link Layer 5-30
CSMA collisions
īļ collisions can still
occur: propagation
delay means two
nodes may not hear
each otherâs
transmission
īļ collision: entire packet
transmission time
wasted
ī§ distance & propagation
delay play role in in
determining collision
probability
spatial layout of nodes
31. Link Layer 5-31
CSMA/CD (collision detection)
CSMA/CD: carrier sensing, deferral as in CSMA
ī§ collisions detected within short time
ī§ colliding transmissions aborted, reducing channel
wastage
īļ collision detection:
ī§ easy in wired LANs: measure signal strengths,
compare transmitted, received signals
ī§ difficult in wireless LANs: received signal strength
overwhelmed by local transmission strength
īļ human analogy: the polite conversationalist
33. Link Layer 5-33
Ethernet CSMA/CD algorithm
1. NIC receives datagram
from network layer,
creates frame
2. If NIC senses channel
idle, starts frame
transmission. If NIC
senses channel busy,
waits until channel idle,
then transmits.
3. If NIC transmits entire
frame without detecting
another transmission,
NIC is done with frame
!
4. If NIC detects another
transmission while
transmitting, aborts
and sends jam signal
5. After aborting, NIC
enters binary
(exponential) backoff:
ī§ after mth collision,
NIC chooses K at
random from {0,1,2,
âĻ, 2m-1}. NIC waits
KÎ512 bit times,
returns to Step 2
ī§ longer backoff interval
with more collisions
34. Link Layer 5-34
CSMA/CD efficiency
īļ Tprop = max prop delay between 2 nodes in LAN
īļ ttrans = time to transmit max-size frame
īļ efficiency goes to 1
ī§ as tprop goes to 0
ī§ as ttrans goes to infinity
īļ better performance than ALOHA: and simple, cheap,
decentralized!
trans
prop /t
t
efficiency
5
1
1
īĢ
īŊ
35. Link Layer 5-35
âTaking turnsâ MAC protocols
channel partitioning MAC protocols:
ī§ share channel efficiently and fairly at high load
ī§ inefficient at low load: delay in channel access,
1/N bandwidth allocated even if only 1 active
node!
random access MAC protocols
ī§ efficient at low load: single node can fully utilize
channel
ī§ high load: collision overhead
âtaking turnsâ protocols
look for best of both worlds!
36. Link Layer 5-36
polling:
īļ master node
âinvitesâ slave nodes
to transmit in turn
īļ typically used with
âdumbâ slave
devices
īļ concerns:
ī§ polling overhead
ī§ latency
ī§ single point of
failure (master)
master
slaves
poll
data
data
âTaking turnsâ MAC protocols
37. Link Layer 5-37
token passing:
īļ control token passed
from one node to next
sequentially.
īļ token message
īļ concerns:
ī§ token overhead
ī§ latency
ī§ single point of failure
(token)
T
data
(nothing
to send)
T
âTaking turnsâ MAC protocols
38. cable headend
CMTS
ISP
cable modem
termination system
īļ multiple 40Mbps downstream (broadcast) channels
ī§ single CMTS transmits into channels
īļ multiple 30 Mbps upstream channels
ī§ multiple access: all users contend for certain upstream
channel time slots (others assigned)
Cable access network
cable
modem
splitter
âĻ
âĻ
Internet frames,TV channels, control transmitted
downstream at different frequencies
upstream Internet frames, TV control, transmitted
upstream at different frequencies in time slots
39. Link Layer 5-39
DOCSIS: data over cable service interface spec
īļ FDM over upstream, downstream frequency channels
īļ TDM upstream: some slots assigned, some have
contention
ī§ downstream MAP frame: assigns upstream slots
ī§ request for upstream slots (and data) transmitted
random access (binary backoff) in selected slots
MAP frame for
Interval [t1, t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modem
upstream data frames
Minislots containing
minislots request frames
cable headend
CMTS
Cable access network
40. Link Layer 5-40
Summary of MAC protocols
īļ channel partitioning, by time, frequency or code
ī§ Time Division, Frequency Division
īļ random access (dynamic),
ī§ ALOHA, S-ALOHA, CSMA, CSMA/CD
ī§ carrier sensing: easy in some technologies (wire),
hard in others (wireless)
ī§ CSMA/CD used in Ethernet
ī§ CSMA/CA used in 802.11
īļ taking turns
ī§ polling from central site, token passing
ī§ bluetooth, FDDI, token ring
41. Link Layer 5-41
Link layer, LANs: outline
5.1 introduction,
services
5.2 error detection,
correction
5.3 multiple access
protocols
5.4 LANs
ī§ addressing, ARP
ī§ Ethernet
ī§ switches
ī§ VLANS
5.5 link virtualization:
MPLS
5.6 data center
networking
5.7 a day in the life of a
web request
42. Link Layer 5-42
MAC addresses and ARP
īļ 32-bit IP address:
ī§ network-layer address for interface
ī§ used for layer 3 (network layer) forwarding
īļ MAC (or LAN or physical or Ethernet) address:
ī§ function: used âlocallyâ to get frame from one interface
to another physically-connected interface (same
network, in IP-addressing sense)
ī§ 48 bit MAC address (for most LANs) burned in NIC
ROM, also sometimes software settable
ī§ e.g.: 1A-2F-BB-76-09-AD
hexadecimal (base 16) notation
(each ânumberâ represents 4 bits)
43. Link Layer 5-43
LAN addresses and ARP
each adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
(wired or
wireless)
44. Link Layer 5-44
LAN addresses (more)
īļ MAC address allocation administered by
IEEE
īļ manufacturer buys portion of MAC address
space (to assure uniqueness)
īļ analogy:
ī§ MAC address: like Social Security Number
ī§ IP address: like postal address
īļ MAC flat address â portability
ī§ can move LAN card from one LAN to another
īļ IP hierarchical address not portable
ī§ address depends on IP subnet to which node is
attached
45. Link Layer 5-45
ARP: address resolution protocol
ARP table: each IP node
(host, router) on LAN has
table
ī§ IP/MAC address
mappings for some
LAN nodes:
< IP address; MAC address;
TTL>
ī§ TTL (Time To Live):
time after which
address mapping will
be forgotten (typically
20 min)
Question: how to determine
interfaceâs MAC address,
knowing its IP address?
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN
137.196.7.23
137.196.7.78
137.196.7.14
137.196.7.88
46. Link Layer 5-46
ARP protocol: same LAN
īļ A wants to send
datagram to B
ī§ Bâs MAC address not in
Aâs ARP table.
īļ A broadcasts ARP
query packet,
containing B's IP
address
ī§ dest MAC address = FF-
FF-FF-FF-FF-FF
ī§ all nodes on LAN receive
ARP query
īļ B receives ARP packet,
replies to A with its (B's)
MAC address
ī§ frame sent to Aâs MAC
address (unicast)
īļ A caches (saves) IP-to-
MAC address pair in its
ARP table until
information becomes
old (times out)
ī§ soft state: information
that times out (goes
away) unless refreshed
īļ ARP is âplug-and-playâ:
ī§ nodes create their ARP
tables without
intervention from net
administrator
47. Link Layer 5-47
walkthrough: send datagram from A to B via R
ī§ focus on addressing â at IP (datagram) and MAC layer
(frame)
ī§ assume A knows Bâs IP address
ī§ assume A knows IP address of first hop router, R (how?)
ī§ assume A knows Râs MAC address (how?)
Addressing: routing to another
LAN
R
1A-23-F9-CD-06-9B
222.222.222.220
111.111.111.110
E6-E9-00-17-BB-4B
CC-49-DE-D0-AB-7D
111.111.111.112
111.111.111.111
74-29-9C-E8-FF-55
A
222.222.222.222
49-BD-D2-C7-56-2A
222.222.222.221
88-B2-2F-54-1A-0F
B
53. Link Layer 5-53
Link layer, LANs: outline
5.1 introduction,
services
5.2 error detection,
correction
5.3 multiple access
protocols
5.4 LANs
ī§ addressing, ARP
ī§ Ethernet
ī§ switches
ī§ VLANS
5.5 link virtualization:
MPLS
5.6 data center
networking
5.7 a day in the life of a
web request
54. Link Layer 5-54
Ethernet
âdominantâ wired LAN technology:
īļ cheap $20 for NIC
īļ first widely used LAN technology
īļ simpler, cheaper than token LANs and ATM
īļ kept up with speed race: 10 Mbps â 10 Gbps
Metcalfeâs Ethernet sketch
55. Link Layer 5-55
Ethernet: physical topology
īļ bus: popular through mid 90s
ī§ all nodes in same collision domain (can collide with
each other)
īļ star: prevails today
ī§ active switch in center
ī§ each âspokeâ runs a (separate) Ethernet protocol
(nodes do not collide with each other)
switch
bus: coaxial cable
star
56. Link Layer 5-56
Ethernet frame structure
sending adapter encapsulates IP datagram (or
other network layer protocol packet) in
Ethernet frame
preamble:
īļ 7 bytes with pattern 10101010 followed by
one byte with pattern 10101011
īļ used to synchronize receiver, sender clock
rates
dest.
address
source
address
data
(payload) CRC
preamble
type
57. Link Layer 5-57
Ethernet frame structure (more)
īļ addresses: 6 byte source, destination MAC
addresses
ī§ if adapter receives frame with matching destination
address, or with broadcast address (e.g. ARP packet),
it passes data in frame to network layer protocol
ī§ otherwise, adapter discards frame
īļ type: indicates higher layer protocol (mostly IP
but others possible, e.g., Novell IPX, AppleTalk)
īļ CRC: cyclic redundancy check at receiver
ī§ error detected: frame is dropped
dest.
address
source
address
data
(payload) CRC
preamble
type
58. Link Layer 5-58
Ethernet: unreliable, connectionless
īļ connectionless: no handshaking between
sending and receiving NICs
īļ unreliable: receiving NIC doesnt send acks or
nacks to sending NIC
ī§ data in dropped frames recovered only if initial
sender uses higher layer rdt (e.g., TCP),
otherwise dropped data lost
īļ Ethernetâs MAC protocol: unslotted CSMA/CD
wth binary backoff
59. Link Layer 5-59
802.3 Ethernet standards: link & physical
layers
īļ many different Ethernet standards
ī§ common MAC protocol and frame format
ī§ different speeds: 2 Mbps, 10 Mbps, 100 Mbps,
1Gbps, 10G bps
ī§ different physical layer media: fiber, cable
application
transport
network
link
physical
MAC protocol
and frame format
100BASE-TX
100BASE-T4
100BASE-FX
100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layer
copper (twister
pair) physical layer
60. Link Layer 5-60
Link layer, LANs: outline
5.1 introduction,
services
5.2 error detection,
correction
5.3 multiple access
protocols
5.4 LANs
ī§ addressing, ARP
ī§ Ethernet
ī§ switches
ī§ VLANS
5.5 link virtualization:
MPLS
5.6 data center
networking
5.7 a day in the life of a
web request
61. Link Layer 5-61
Ethernet switch
īļ link-layer device: takes an active role
ī§ store, forward Ethernet frames
ī§ examine incoming frameâs MAC address,
selectively forward frame to one-or-more
outgoing links when frame is to be forwarded
on segment, uses CSMA/CD to access
segment
īļ transparent
ī§ hosts are unaware of presence of switches
īļ plug-and-play, self-learning
ī§ switches do not need to be configured
62. Link Layer 5-62
Switch: multiple simultaneous
transmissions
īļ hosts have dedicated, direct
connection to switch
īļ switches buffer packets
īļ Ethernet protocol used on
each incoming link, but no
collisions; full duplex
ī§ each link is its own
collision domain
īļ switching: A-to-Aâ and B-to-
Bâ can transmit
simultaneously, without
collisions
switch with six interfaces
(1,2,3,4,5,6)
A
Aâ
B
Bâ C
Câ
1 2
3
4
5
6
63. Link Layer 5-63
Switch forwarding table
Q: how does switch know Aâ
reachable via interface 4, Bâ
reachable via interface 5?
switch with six interfaces
(1,2,3,4,5,6)
A
Aâ
B
Bâ C
Câ
1 2
3
4
5
6
īļ A: each switch has a
switch table, each entry:
ī§ (MAC address of host,
interface to reach host, time
stamp)
ī§ looks like a routing table!
Q: how are entries created,
maintained in switch table?
ī§ something like a routing
protocol?
64. A
Aâ
B
Bâ C
Câ
1 2
3
4
5
6
Link Layer 5-64
Switch: self-learning
īļ switch learns which
hosts can be reached
through which interfaces
ī§ when frame received,
switch âlearnsâ
location of sender:
incoming LAN
segment
ī§ records
sender/location pair in
switch table
A Aâ
Source: A
Dest: Aâ
MAC addr interface TTL
Switch table
(initially empty)
A 1 60
65. Link Layer 5-65
Switch: frame filtering/forwarding
when frame received at switch:
1. record incoming link, MAC address of sending host
2. index switch table using MAC destination address
3. if entry found for destination
then {
if destination on segment from which frame arrived
then drop frame
else forward frame on interface indicated by
entry
}
else flood /* forward on all interfaces except
arriving
interface */
66. A
Aâ
B
Bâ C
Câ
1 2
3
4
5
6
Link Layer 5-66
Self-learning, forwarding: example
A Aâ
Source: A
Dest: Aâ
MAC addr interface TTL
switch table
(initially empty)
A 1 60
A Aâ
A Aâ
A Aâ
A Aâ
A Aâ
īļ frame destination, Aâ,
locaton unknown:flood
Aâ A
īļ destination A location
known:
Aâ 4 60
selectively
send
on just one link
67. Link Layer 5-67
Interconnecting switches
īļ switches can be connected together
Q: sending from A to G - how does S1 know to
forward frame destined to F via S4 and S3?
īļ A: self learning! (works exactly the same as in
single-switch case!)
A
B
S1
C D
E
F
S2
S4
S3
H
I
G
68. Link Layer 5-68
Self-learning multi-switch
example
Suppose C sends frame to I, I responds to C
īļ Q: show switch tables and packet forwarding in S1,
S2, S3, S4
A
B
S1
C D
E
F
S2
S4
S3
H
I
G
70. Link Layer 5-70
Switches vs. routers
both are store-and-forward:
ī§ routers: network-layer
devices (examine
network-layer headers)
ī§ switches: link-layer
devices (examine link-
layer headers)
both have forwarding
tables:
ī§ routers: compute tables
using routing algorithms,
IP addresses
ī§ switches: learn
forwarding table using
flooding, learning, MAC
addresses
application
transport
network
link
physical
network
link
physical
link
physical
switch
datagram
application
transport
network
link
physical
frame
frame
frame
datagram
71. Link Layer 5-71
VLANs: motivation
consider:
īļ CS user moves office to
EE, but wants connect to
CS switch?
īļ single broadcast
domain:
ī§ all layer-2 broadcast
traffic (ARP, DHCP,
unknown location of
destination MAC
address) must cross
entire LAN
ī§ security/privacy,
efficiency issues
Computer
Science Electrical
Engineering
Computer
Engineering
72. Link Layer 5-72
VLANs
port-based VLAN: switch ports
grouped (by switch
management software) so that
single physical switch âĻâĻ
switch(es) supporting
VLAN capabilities can
be configured to
define multiple virtual
LANS over single
physical LAN
infrastructure.
Virtual Local
Area Network
1
8
9
16
10
2
7
âĻ
Electrical Engineering
(VLAN ports 1-8)
Computer Science
(VLAN ports 9-15)
15
âĻ
Electrical Engineering
(VLAN ports 1-8)
âĻ
1
8
2
7 9
16
10
15
âĻ
Computer Science
(VLAN ports 9-16)
âĻ operates as multiple virtual
switches
73. Link Layer 5-73
Port-based VLAN
1
8
9
16
10
2
7
âĻ
Electrical Engineering
(VLAN ports 1-8)
Computer Science
(VLAN ports 9-15)
15
âĻ
īļ traffic isolation: frames
to/from ports 1-8 can only
reach ports 1-8
ī§ can also define VLAN based on
MAC addresses of endpoints,
rather than switch port
īļ dynamic membership:
ports can be dynamically
assigned among VLANs
router
īļ forwarding between VLANS:
done via routing (just as with
separate switches)
ī§ in practice vendors sell combined
switches plus routers
74. Link Layer 5-74
VLANS spanning multiple
switches
īļ trunk port: carries frames between VLANS defined over
multiple physical switches
ī§ frames forwarded within VLAN between switches canât be vanilla
802.1 frames (must carry VLAN ID info)
ī§ 802.1q protocol adds/removed additional header fields for frames
forwarded between trunk ports
1
8
9
10
2
7
âĻ
Electrical Engineering
(VLAN ports 1-8)
Computer Science
(VLAN ports 9-15)
15
âĻ
2
7
3
Ports 2,3,5 belong to EE VLAN
Ports 4,6,7,8 belong to CS VLAN
5
4 6 8
16
1
75. Link Layer 5-75
type
2-byte Tag Protocol Identifier
(value: 81-00)
Tag Control Information (12 bit VLAN ID field,
3 bit priority field like IP TOS)
Recomputed
CRC
802.1Q VLAN frame format
802.1 frame
802.1Q frame
dest.
address
source
address
data (payload) CRC
preamble
dest.
address
source
address
preamble data (payload) CRC
type
76. Link Layer 5-76
Link layer, LANs: outline
5.1 introduction,
services
5.2 error detection,
correction
5.3 multiple access
protocols
5.4 LANs
ī§ addressing, ARP
ī§ Ethernet
ī§ switches
ī§ VLANS
5.5 link virtualization:
MPLS
5.6 data center
networking
5.7 a day in the life of a
web request
77. Link Layer 5-77
Multiprotocol label switching (MPLS)
īļ initial goal: high-speed IP forwarding using
fixed length label (instead of IP address)
ī§ fast lookup using fixed length identifier (rather than
shortest prefix matching)
ī§ borrowing ideas from Virtual Circuit (VC) approach
ī§ but IP datagram still keeps IP address!
PPP or Ethernet
header
IP header remainder of link-layer frame
MPLS header
label Exp S TTL
20 3 1 5
78. Link Layer 5-78
MPLS capable routers
īļ a.k.a. label-switched router
īļ forward packets to outgoing interface based only
on label value (donât inspect IP address)
ī§ MPLS forwarding table distinct from IP forwarding
tables
īļ flexibility: MPLS forwarding decisions can differ
from those of IP
ī§ use destination and source addresses to route flows to
same destination differently (traffic engineering)
ī§ re-route flows quickly if link fails: pre-computed backup
paths (useful for VoIP)
80. Link Layer 5-80
R2
D
R3
R4
R5
A
R6
MPLS versus IP paths
IP-only
router
īļ IP routing: path to destination
determined by destination address
alone MPLS and
IP router
īļ MPLS routing: path to destination
can be based on source and dest.
address
ī§ fast reroute: precompute backup
routes in case of link failure
entry router (R4) can use different MPLS
routes to A based, e.g., on source address
81. Link Layer 5-81
MPLS signaling
īļ modify OSPF, IS-IS link-state flooding protocols
to carry info used by MPLS routing,
ī§ e.g., link bandwidth, amount of âreservedâ link
bandwidth
D
R4
R5
A
R6
īļ entry MPLS router uses RSVP-TE signaling
protocol to set up MPLS forwarding at
downstream routers
modified
link state
flooding
RSVP-TE
82. Link Layer 5-82
R1
R2
D
R3
R4
R5
0
1
0
0
A
R6
in out out
label label dest interface
6 - A 0
in out out
label label dest interface
10 6 A 1
12 9 D 0
in out out
label label dest interface
10 A 0
12 D 0
1
in out out
label label dest interface
8 6 A 0
0
8 A 1
MPLS forwarding tables
83. Link Layer 5-83
Link layer, LANs: outline
5.1 introduction,
services
5.2 error detection,
correction
5.3 multiple access
protocols
5.4 LANs
ī§ addressing, ARP
ī§ Ethernet
ī§ switches
ī§ VLANS
5.5 link virtualization:
MPLS
5.6 data center
networking
5.7 a day in the life of a
web request
84. Link Layer 5-84
Data center networks
īļ 10âs to 100âs of thousands of hosts, often closely
coupled, in close proximity:
ī§ e-business (e.g. Amazon)
ī§ content-servers (e.g., YouTube, Akamai, Apple,
Microsoft)
ī§ search engines, data mining (e.g., Google)
īļ challenges:
ī§ multiple applications, each
serving massive numbers
of clients
ī§ managing/balancing load,
avoiding processing,
networking, data
bottlenecks Inside a 40-ft Microsoft container,
Chicago data center
85. Link Layer 5-85
Server racks
TOR switches
Tier-1 switches
Tier-2 switches
Load
balancer
Load
balancer
B
1 2 3 4 5 6 7 8
A C
Border router
Access router
Internet
Data center networks
load balancer: application-layer
routing
ī§ receives external client requests
ī§ directs workload within data center
ī§ returns results to external client (hiding
data center internals from client)
86. Server racks
TOR switches
Tier-1 switches
Tier-2 switches
1 2 3 4 5 6 7 8
Data center networks
īļ rich interconnection among switches, racks:
ī§ increased throughput between racks (multiple routing
paths possible)
ī§ increased reliability via redundancy
87. Link Layer 5-87
Link layer, LANs: outline
5.1 introduction,
services
5.2 error detection,
correction
5.3 multiple access
protocols
5.4 LANs
ī§ addressing, ARP
ī§ Ethernet
ī§ switches
ī§ VLANS
5.5 link virtualization:
MPLS
5.6 data center
networking
5.7 a day in the life of a
web request
88. Link Layer 5-88
Synthesis: a day in the life of a web request
īļ journey down protocol stack complete!
ī§ application, transport, network, link
īļ putting-it-all-together: synthesis!
ī§ goal: identify, review, understand protocols (at all
layers) involved in seemingly simple scenario:
requesting www page
ī§ scenario: student attaches laptop to campus
network, requests/receives www.google.com
89. Link Layer 5-89
A day in the life: scenario
Comcast network
68.80.0.0/13
Googleâs network
64.233.160.0/19
64.233.169.105
web server
DNS server
school network
68.80.2.0/24
web page
browser
90. router
(runs DHCP)
Link Layer 5-90
A day in the lifeâĻ connecting to the
Internet
īļ connecting laptop needs
to get its own IP address,
addr of first-hop router,
addr of DNS server: use
DHCP
DHCP
UDP
IP
Eth
Phy
DHCP
DHCP
DHCP
DHCP
DHCP
DHCP
UDP
IP
Eth
Phy
DHCP
DHCP
DHCP
DHCP
DHCP
īļ DHCP request
encapsulated in UDP,
encapsulated in IP,
encapsulated in 802.3
Ethernet
īļ Ethernet frame broadcast
(dest: FFFFFFFFFFFF) on
LAN, received at router
running DHCP server
īļ Ethernet demuxed to IP
demuxed, UDP demuxed
to DHCP
91. router
(runs DHCP)
Link Layer 5-91
īļ DHCP server formulates
DHCP ACK containing
clientâs IP address, IP
address of first-hop router
for client, name & IP
address of DNS server
DHCP
UDP
IP
Eth
Phy
DHCP
DHCP
DHCP
DHCP
DHCP
UDP
IP
Eth
Phy
DHCP
DHCP
DHCP
DHCP
DHCP
īļ encapsulation at DHCP
server, frame forwarded
(switch learning) through
LAN, demultiplexing at
client
Client now has IP address, knows name & addr of DNS
server, IP address of its first-hop router
īļ DHCP client receives
DHCP ACK reply
A day in the lifeâĻ connecting to the
Internet
92. router
(runs DHCP)
Link Layer 5-92
A day in the lifeâĻ ARP (before DNS, before
HTTP)
īļ before sending HTTP request,
need IP address of
www.google.com: DNS
DNS
UDP
IP
Eth
Phy
DNS
DNS
DNS
īļ DNS query created,
encapsulated in UDP,
encapsulated in IP,
encapsulated in Eth. To send
frame to router, need MAC
address of router interface: ARP
īļ ARP query broadcast,
received by router, which
replies with ARP reply giving
MAC address of router
interface
īļ client now knows MAC
address of first hop router, so
can now send frame
containing DNS query
ARP query
Eth
Phy
ARP
ARP
ARP reply
93. router
(runs DHCP)
Link Layer 5-93
DNS
UDP
IP
Eth
Phy
DNS
DNS
DNS
DNS
DNS
īļ IP datagram containing
DNS query forwarded via
LAN switch from client to
1st hop router
īļ IP datagram forwarded from
campus network into comcast
network, routed (tables created
by RIP, OSPF, IS-IS and/or
BGP routing protocols) to DNS
server
īļ demuxâed to DNS server
īļ DNS server replies to
client with IP address of
www.google.com
Comcast network
68.80.0.0/13
DNS server
DNS
UDP
IP
Eth
Phy
DNS
DNS
DNS
DNS
A day in the lifeâĻ using DNS
94. router
(runs DHCP)
Link Layer 5-94
A day in the lifeâĻTCP connection carrying
HTTP
HTTP
TCP
IP
Eth
Phy
HTTP
īļ to send HTTP request,
client first opens TCP
socket to web server
īļ TCP SYN segment (step 1
in 3-way handshake) inter-
domain routed to web server
īļ TCP connection established!
64.233.169.105
web server
SYN
SYN
SYN
SYN
TCP
IP
Eth
Phy
SYN
SYN
SYN
SYNACK
SYNACK
SYNACK
SYNACK
SYNACK
SYNACK
SYNACK
īļ web server responds with
TCP SYNACK (step 2 in 3-
way handshake)
95. router
(runs DHCP)
Link Layer 5-95
A day in the lifeâĻ HTTP request/reply
HTTP
TCP
IP
Eth
Phy
HTTP
īļ HTTP request sent into
TCP socket
īļ IP datagram containing
HTTP request routed to
www.google.com
īļ IP datagram containing HTTP
reply routed back to client
64.233.169.105
web server
HTTP
TCP
IP
Eth
Phy
īļ web server responds with
HTTP reply (containing web
page)
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
HTTP
īļ web page finally (!!!)
displayed
96. Link Layer 5-96
Chapter 5: Summary
īļ principles behind data link layer services:
ī§ error detection, correction
ī§ sharing a broadcast channel: multiple access
ī§ link layer addressing
īļ instantiation and implementation of various link
layer technologies
ī§ Ethernet
ī§ switched LANS, VLANs
ī§ virtualized networks as a link layer: MPLS
īļ synthesis: a day in the life of a web request
97. Link Layer 5-97
Chapter 5: letâs take a breath
īļ journey down protocol stack complete (except
PHY)
īļ solid understanding of networking principles,
practice
īļ âĻ.. could stop here âĻ. but lots of interesting
topics!
ī§ wireless
ī§ multimedia
ī§ security
ī§ network management