Chapter 1d dhioa sa hioas hao sajho bjj

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

Accessing the WAN


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

Chapter 1 Introduction to WANs

When an enterprise grows, it is essential to have WideArea Network (WAN) access to support its:-

communications among branch offices

e-commerce services global operations

There are a variety of WAN technologies to meetdifferent needs of businesses and many ways to scale

the network However, adding WAN access introduces other issues

like network security and address management


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Objectives

Describe how the Cisco Enterprise CompositeModel (ECNM) provides integrated servicesover an Enterprise network.

Describe the key WAN technology concepts. Identify the appropriate WAN technologies to

use when matching ECNM best practices withtypical enterprise requirements for WAN

communications.


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Introducing to Wide Area Networks (WANs)

WAN a data communications network that operatesbeyond the geographic scope of a LAN


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Differences between a LAN and a WAN

LANs WANs

1. Connect computers, peripherals

and other devices in a small

building or small geographical

area.

1. Connect devices that are

separated by a broader

geographical area than can be

served by a LAN.

2. Typically owned by the company

organisation that uses them.

2. Use the services of carriers, such

as telephone companies, cable

companies, satellite systems, and

network providers.

3. Use serial connections of various

types to provide access to

bandwidth over large geographic

areas.


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The Evolving Enterprise

Various stages of growth for a business and its network:

Small Office (Single LAN)


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Various stages of growth for a business and its network(cont):

Campus (Multiple LANs)

Instead of a single small LAN, the network now consists ofseveral subnetworks, each devoted to a different department.For example, all the engineering staff are on one LAN, whilethe marketing staff is on another LAN. These multiple LANsare joined to create a company-wide network, or campus,which spans several floors of the building.




Various stages of growth for a business and its network(cont):

Branch (WAN)

Distributed (Global)



The Evolving Network Model

The Hierarchical Network Model

- a useful high-level tool for designing a reliable networkinfrastructure.

- provides a modular view of a network, making it easier todesign and build a scalable network.

- Divides a network into three layers:-

- Access

- Distribution

- Core



The Enterprise Architecture

-Different businesses need different type of networks,depending on how the business is operated and its goals.

-As business grows, often new components are added inresponse to immediate needs.

-This will create a mixture of newer and older technologies,which can be difficult to maintain and support.

-Outages and poor performance are a constant source of

trouble for network administrator.-To prevent this situation, Cisco has developed CiscoEnterprise Architecture that has relevance to different stagesof business growth.




The Enterprise Architecturecont

- to provide a roadmap for network growth as the businessmoves through different stages.

-By following the suggested roadmap, IT managers can plan forfuture network upgrades that will integrate newer and oldernetworks and support for future growth.

-Some examples of the module within the architecture:-

- Enterprise Campus Architecture

- Enterprise Branch Architecture

- Enterprise Data Centre Architecture

- Enterprise Teleworker Architecture




Cisco Enterprise Architectures



Modules in the Enterprise Architecture

es

Example Topology

Enterprise Architecture



Enterprise Campus Architecture

Is a building or group of buildings connected to 1enterprise network that consists of many LANs.

A campus is generally limited to a fixed geographic

area, but it can span several neighboring buildings. e.g. industrial complex or business park environment

Describes the recommended methods to create ascalable network while addressing the requirements of

campus style operations.

Is modular and can easily expand to include additionalcampus buildings or floors as the enterprise grows.



Enterprise Edge Architecture

Offers connectivity to voice, video and data servicesoutside the enterprise.

Enables the enterprise to use Internet and partners

resources and provide resources for its customers.

Often function as a liaison between the campus andother modules in the Enterprise architecture.



Enterprise Branch Architecture

Allows businesses to extend the applications andservices found at the campus to remote branches



Enterprise Data Center Architecture

Responsible for managing and maintaining the manydata systems that are vital to modern businessoperations.

Users rely on data and resources in data center toeffectively create, collaborate and interact.



Enterprise Teleworker Architecture

Many businesses today allow their employees totelecommute from home offices.

To telecommute is leverage the network resources of

the enterprise from home

Recommends to use cable modem / DSL to connect tothe corporate network from home via Internet.

However, special security measures need to be takento ensure secure and private communications asInternet introduces additional security risks.



WAN Technology Overview



WANs and the OSI Model

In relation to the OSI reference model, WAN operationsfocus primarily on Layer 1 and Layer 2.

Layer 1 protocols describe how to provide electrical,

mechanical, operational and functional connections tothe services of a communication service provider.

Layer 2 protocols define how data is encapsulated fortransmission toward a remote location and the

mechanisms for transferring the resulting frames. A variety of different technologies are used, such as Frame

Relay and ATM. Some of these protocols use the same basicframing mechanism, High-Level Data Link Control (HDLC), anISO standard, or one of its subsets or variants.



WAN Technology Concepts

WAN physical layer concepts for network and Internetcommunications



WAN Physical Layer Concepts

1 primary difference between a LAN and a WAN is thatan organization must subscribe to an outside serviceprovider to use WAN carrier network services.

A WAN uses data links provided by carrier services toaccess the Internet and connects to:-

the locations of an organization to each other

locations of other organizations

external services

remote users

The WAN access physical layer describes the physicalconnections between the company network and theservice provider network.



WAN Physical Layer Terminology

Customer Premises Equipment (CPE)

the devices and inside wiring located at the subscriberspremises and connected with a telecommunication channel ofa carrier.

can be either owned by the subscriber or leased from theservice provider.

A subscriber -> a company that arranges for WAN servicesfrom a service provider or carrier




Data Communications Equipment (DCE)

also called data circuit-terminating equipment

consists of devices that put data on the local loop

primarily provides an interface to connect subscriber to acommunication link on the WAN cloud

Data Terminal Equipment (DTE)

The customer devices that pass the data from a customernetwork or host computer fro transmission over the WAN

Connects to the local loop through the DCE


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Demarcation Point

A point established in a building/complex to separatecustomers equipment from service providers equipment

Is the cabling junction box, located at the customer premises,

that connects the CPE wiring to the local loop

Local Loop

The copper/fiber telephone cable that connects the CPE at thesubscriber site to the CO of the service provider

Is also called the last-mile

Central Office (CO)

A local service provider facility/building where local telephonecables link to long-haul, all digital, fiber-optic communicationlines through a system of switches and other equipments


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WAN Devices

Modem

Modulates an analog carrier signal to encode digitalinformation and also demodulates the carrier signal to decodethe transmitted information.

Faster modems such as cable modems and DSL modemstransmit using higher broadband frequencies.

CSU/DSU

CSU provides termination for the digital signal and ensuresconnection integrity thru error correction and line monitoring.

DSU converts the T-carrier line frames into frames that theLAN can interpret and vice versa.

Are often combined into a single piece of equipment


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WAN Devices

Access Server

Concentrates dial-in and dial-out user communications.

May have a mixture of analog and digital interfaces andsupport hundreds of simultaneous users

WAN Switch

A multiport internetworking device used in carrier networks

Typically switches traffic such as Frame Relay, ATM, or X.25

Operates at the data link layer of the OSI reference model


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WAN Devices

Router

Provides internetworking and WAN access interface ports thatare used to connect to the service provider network.

Core Router

Resides within the middle or backbone of the WAN rather thanat its periphery

Must be able to support multiple telecommunication interfacesof the highest speed in use in the WAN core

Must be able to forward IP packets at full speed on all of theseinterfaces.

Must also support the routing protocols being used in the core.


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In addition to Physical layer devices, WANs require Data Link layerprotocols to establish the link across the communication line fromthe sending to the receiving device.

Data Link Protocols

Establish the link across the communication line from the sending toreceiving devices.

Define how data is encapsulated for transmission to remote sites andthe mechanisms for transferring the resulting frames.

There are a variety of technologies used such as ISDN, Frame Relayor ATM.

Many of these protocols use the same framing mechanism HDLC, anISO standard or one of its subsets or variants.

The most common WAN data link protocol are:

HDLC

PPP

Frame Relay

ATM

WAN Data Link Layer Concepts


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Switching technologies used for WANs in an Enterprisesetting


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WAN Encapsulation

Data from the network layer is passed to the data link layer fordelivery on physical link, normally point-to-point on a WANconnection.

The data link layer builds a frame around the network layer dataso that necessary checks and controls can be applied.

Each WAN connection type uses layer 2 protocol toencapsulate a packet while it is crossing the WAN link.

The choice of encapsulation protocols depends on the WAN

technology and the equipment.HLDC was first proposed in 1979, thus most framing protocols

that were developed after that are based on it.


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WAN Frame Encapsulation FormatsFrame always starts and ends with an 8-bit flag field.

The bit pattern is 01111110.

The address field is not needed for WAN links, which are almostalways point-to-point.

The control field is protocol dependent indicates whether the contentof data is control information or network layer data. It is normally 1byte.

The address and control fields are called the frame header.

The encapsulated data follows the control field.

Then a Frame Check Sequence (CFS) uses the cyclic redundancycheck (CRC) mechanism to establish a 2 or 4 byte field.

Both PPP and Cisco version of HDLC have an extra field in the headerto identify the network layer protocol of the encapsulated data.


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WAN Switching Concepts


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Circuit Switching

A circuit switched network establishes a dedicated circuit (orchannel) between nodes and terminals before the users maycommunicate.

Generally an expensive way of moving data

Examples :- PSTN and ISDN.


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Packet Switching

Splits traffic data into packets that are routed over a sharednetwork.

Packet switching networks do not require a circuit to beestablished and they allow many pairs of node to communicateover the same channel.

The switches in the packet-switched network determine whichlink the packet must be sent on the next from the addressinginformation in each packet.

There are two approaches to determine the link:-

Connectionless

Connection-oriented


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Connectionless

Such as the Internet, carry full addressing information in eachpacket.

Each switch must evaluate the address to determine where tosend the packet.

Connection-oriented

Predetermines the route for a packet, and each packet only hasto carry an identifier.

The switch determines the onward route by looking up theidentifier in tables held in memory.

The set of entries in the tables identifies a particular route orcircuit through the system.


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WAN Link Connection Options


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Dedicated Connection Link Options

When permanent dedicated connections are required, apoint-to-point link is used to provide a pre-establishedWAN communications path from the customerpremises through the provider network to a remotedestination.

Point-to-point lines are usually leased from a carrierand are called leased lines.

Leased lines are available in different capacities and

are generally priced based on the bandwidth requiredand the distance between the two connected points.


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Dedicated Connection Link Options


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Circuit Switched Connection Options


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Packet Switched Connection Options


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Choosing a WAN Link Connection

List factors to consider when selecting a WANconnection


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Summary

A WAN is defined as

A data communications network that operates beyond thegeographic 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


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Summary

Cisco Enterprise Architecture

This is an expansion of the hierarchical model that furtherdivides the enterprise network into

Physical areas

Logical areas

Functional areas

Selecting the appropriate WAN technology requiresconsidering some of the following:

WANs purpose

Geographic scope of WANTraffic requirements

If WAN uses a public or private infrastructure


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Chapter 1d dhioa sa hioas hao sajho bjj

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