Information Technology Reference
In-Depth Information
This chapter describes the WAN topics that you need to master for the CCDA exam.
These topics include the WAN modules included in the enterprise edge, WAN technolo-
gies, WAN technology selection considerations, and WAN design methodologies. In addi-
tion, this chapter describes quality of service (QoS) and how it can be used to prioritize
network traffic and better utilize the available WAN bandwidth.
WA N s p r o v i d e n e t w o r k c o n n e c t i v i t y f o r t h e e n t e r p r i s e e d g e , r e m o t e b r a n c h e d g e l o c a -
tions, and the Internet. Many WAN choices are available, and new ones are continually
emerging. When you are selecting WAN transport technologies, it is important to con-
sider factors such as cost, bandwidth, reliability, manageability, and hardware capabilities.
In addition, enterprise branch offices can take advantage of cable and digital subscriber
line (DSL) technologies for remote virtual private network (VPN) connectivity back to the
headquarters or main office.
WAN D efine d
Wide-area networks (WAN) are communications networks that are used to connect geo-
graphically disperse network locations. Generally, WAN services are offered by service
providers or telecommunication carriers. WANs can transport data, voice, and video traf-
fic. Service providers charge fees, called tariffs, for providing WAN services or communi-
cations to their customers. Sometimes the term
service
is referred to as the WAN
communications provided by the carrier.
When designing a WAN, you should become familiar with the design's requirements,
which typically derive from these two important goals:
Key
To p i c
Service level agreement (SLA):
Defines the availability of the network. Net-
worked applications rely on the underlying network between the client and server to
provide its functions. There are multiple levels of application availability that can be
part of a negotiated SLA with a service provider. Organizations have to work with the
carrier to define what level of service, such as bandwidth, allowed latency, and loss, is
acceptable to the organization.
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Cost and usage:
To s e l e c t t h e c o r r e c t r e l i a b l e WA N s e r v i c e , y o u m u s t c o n s i d e r t h e
budget and usage requirements of the WAN service.
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There are three key objectives of an effective WAN design:
The WAN needs to support the goals and policies of the organization.
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The WAN technologies selected needs to meet the current application requirements
and provide for growth of the organization in the future.
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The proposed design should stay with the budget that is allocated for the WA N design
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Figure 6-1 shows a typical enterprise edge with Multiprotocol Label Switching (MPLS)
and Internet WAN connections.