Chapter1 rev1.0

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

Services in a Converged WAN

Accessing the WAN – Chapter 1

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

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.


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

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.

Ex: ISDN and PSTN


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 asA 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


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