Chapter1 rev1.0

Services in a
Converged WAN

Accessing the WAN – Chapter 1

ITE I Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 1

Objectives
 Describe how the Cisco Enterprise Composite
Model (ECNM) provides integrated services
over an Enterprise network.
 Describe the key WAN technology concepts.
 Identify the appropriate WAN technologies to
use when matching ECNM best practices with
typical enterprise requirements for WAN
communications.

ITE 1 Chapter 6 © 2006 Cisco Systems, Inc. All rights reserved. Cisco Public 2

1.1 Providing Integrated
Services to the Enterprise



The purpose and function of WANs


The purpose and function of WANs
 A WAN is a data communications network that
operates beyond the geographic scope of a LAN.
Characteristics include:
 Connect devices that are separated by a broader
geographical area than can be served by a LAN.
 Use the services of carriers, such as telephone
companies, cable companies, satellite systems, and
network providers.
 Use serial connections of various types to provide
access to bandwidth over large geographic areas.


The Evolving Enterprise Network
•Network requirements of a
company can change
dramatically as the company
grows over time.


The Hierarchical Design Model

Access layer - Grants user access to network devices.
Distribution layer - aggregates WAN connections at the
edge of the campus and provides policy-based connectivity.
Core layer - high-speed backbone that is designed to switch
packets as fast as possible.

Cisco Enterprise Architecture

An architecture
developed by Cisco that
has relevance to the
different stages of
growth of a business.

The Cisco Enterprise Architecture consists of modules
representing focused views that target each place in the network.
Each module has a distinct network infrastructure with services
and network applications that extend across the modules.

Modules in the Enterprise Architecture
•Enterprise Campus Architecture - describes the recommended
methods to create a scalable network, while addressing the
needs of campus-style business operations.

•Enterprise Edge Architecture - enables the enterprise to use
Internet and partner resources, and provide resources for its
customers.

•Enterprise Branch Architecture - allows businesses to extend the
applications and services found at the campus to remote
locations and users or to a small group of branches.

•Enterprise Data Center Architecture – manages and maintains
centralized data systems for the entire enterprise

•Enterprise Teleworker Architecture – connects individual
employees to network resources remotely, typically from home.

1.2 WAN technology
overview



Describe the Key WAN Technology
Concepts

WAN operations focus primarily on Layer 1 and Layer 2.


WAN Physical Layer Terminology

 Customer Premises
Equipment
 Data
Communications
Equipment
 Data Terminal
Equipment
 Demarcation Point


 Customer Premises Equipment - Devices and inside
wiring located at the premises of the subscriber and
connected with a telecommunication channel of a
carrier.
 Data Communications Equipment - consists of devices
that put data on the local loop
 Data Terminal Equipment - customer devices that pass
the data from a customer network or host computer for
transmission over the WAN.
 Demarcation Point - a point established in a building or
complex to separate customer equipment from service
provider equipment.

 Local loop - the copper or fiber telephone cable that
connects the CPE at the subscriber site to the CO of
the service provider; also called last mile
 Central Office - a local service provider facility or
building where local telephone cables link to long-haul,
all-digital, fiber-optic communications lines through a
system of switches and other equipment.


WAN Devices


WAN Devices
 Modem - Modulates an analog carrier signal to encode
digital information, and also demodulates the carrier
signal to decode the transmitted information.
 CSU/DSU- used on T1 and T3 lines; The CSU
provides termination for the digital signal and ensures
integrity through error correction. The DSU converts
the T-carrier line frames into frames that the LAN can
interpret.
 Access Server - concentrates dial-in and dial-out user
communications.


WAN Devices
 WAN switch - a multiport internetworking device used
in carrier networks; typically switches traffic like Frame
Relay, ATM, or X.25; operates at the data link layer of
the OSI model
 Modem - Modulates an analog carrier signal to encode
digital information, and also demodulates the carrier
signal to decode the transmitted information.
 Router- provides internetworking and WAN access
interface ports that are used to connect to the service
provider network.
 Core router-A router that resides within the middle or
backbone of the WAN

WAN Physical Layer Standards


 EIA/TIA-232- allows signal speeds of up to 64 kbps on
a 25-pin D-connector over short distances
(RS232/V.24)
 EIA/TIA-449/530 - a faster version of EIA/TIA-232. It
uses a 36-pin D-connector and is capable of longer
cable runs.
 EIA/TIA-612/613 - Describes the High-Speed Serial
Interface (HSSI) protocol, which provides access to
services up to 52 Mb/s on a 60-pin D-connector.


 V.35 - the ITU-T standard for synchronous
communications between a network access device and
a packet network.
 X.21 - an ITU-T standard for synchronous digital
communications. It uses a 15-pin D-connector.


WAN Data Link Layer Standards


WAN Frame Encapsulation Formats


Circuit Switching

Ex: ISDN and
PSTN

 A circuit-switched network is one that establishes a
dedicated circuit between nodes and terminals before the
users may communicate.
 The internal path taken by the circuit between exchanges
is shared by a number of conversations. Time division
multiplexing (TDM) gives each conversation a share of
the connection in turn.


Packet Switching


Packet Switching
 Packet switching splits traffic data into packets that are
routed over a shared network.
 Packet-switching networks do not require a circuit to be
established, and they allow many pairs of nodes to
communicate over the same channel.
 The switches in a packet-switched network determine which
link the packet must be sent on next from the addressing
information in each packet.
 Packet-switched networks may establish routes through the
switches for particular end-to-end connections called virtual
circuits. A VC is a logical circuit created within a shared
network between two network devices. Two types of VCs
exist: PVC and SVC (more on Ch. 3)


1.3 Internet Connection Options



Various options for connecting subscribers to the WAN


Leased line


Circuit switching options


Packet switching options

X25
Frame Relay
ATM


Broadband Services
 ADSL
 Cable
 Wireless (WiMax)


VPN Technology


Metro Ethernet


Factors to consider when selecting a WAN
connection


Factors to consider when selecting a WAN
connection (cont.)


Summary

 A WAN is defined as
A data communications network that operates beyond the
geographic scope of a LAN
 WAN primarily operate on layer 1 & 2 of the OSI model
 WAN technologies include
–Leased line
–ISDN
–Frame relay
–X.25
–ATM


Summary
 Cisco Enterprise Architecture
–This is an expansion of the hierarchical model that further
divides the enterprise network into
•Physical areas
•Logical areas
•Functional areas

 Selecting the appropriate WAN technology requires
considering some of the following:
–WAN’s purpose
–Geographic scope of WAN
–Traffic requirements
–If WAN uses a public or private infrastructure


Next Module


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