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<td bgcolor="#336666"><font face="Arial" size="2" color="#FFFFFF"><b>2.</b></font><b><font face="Arial" size="2" color="#FFFFFF">3</font></b></td>
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<td bgcolor="#336666" width="100%"><strong>
<font face="Arial" size="2" color="#FFFFFF">WAN Design</font></strong></td>
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<td bgcolor="#669999" height="25"><b><font face="Arial" size="2" color="#FFFFFF">
2.3.2</font></b></td>
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<td bgcolor="#669999" height="25" width="100%"><strong>
<font face="Arial" size="2" color="#FFFFFF">Steps in WAN design</font></strong></td>
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<p><font size="2" face="Arial">Designing a WAN can be a challenging task, but
approaching the design in a systematic manner can lead to superior
performance at a reduced cost. Many WANs have evolved over time,
therefore many of the guidelines discussed here may not have been
considered. Every time a modification to an existing WAN is
considered, the steps in this module should be followed. WAN
modifications may arise from changes such as an expansion in the
enterprise the WAN serves, or accommodation of new work practices and
business methods.</font></p>
<p><font size="2" face="Arial">Enterprises install WAN connectivity
because there is a need to move data in a timely manner between
external branches. The WAN is there to support the enterprise
requirements. Meeting these requirements incurs costs, such as
equipment provisioning and management of the data links.</font></p>
<p><font size="2" face="Arial">In designing the WAN, it is necessary to know what data traffic must
be carried, its origin, and its destination. WANs carry a variety of
traffic types with varying requirements for bandwidth, latency, and
jitter. <img border="0" src="../../images/1.gif" align="absmiddle" width="12" height="12"></font></p>
<p><font size="2" face="Arial">For each pair of end points and for each traffic type, information is
needed on the various traffic characteristics.
<img border="0" src="../../images/2.gif" align="absmiddle" width="12" height="12"> Determining this may
involve extensive studies of and consultation with the network users.
The design often involves upgrading, extending, or modifying an
existing WAN. Much of the data needed can come from existing network
management statistics.</font></p>
<p><font size="2" face="Arial">Knowing the various end points allows the selection of a topology or
layout for the WAN. The topology will be influenced by geographic
considerations but also by requirements such as availability. A high
requirement for availability will require extra links that provide
alternative data paths for redundancy and load balancing.</font></p>
<p><font size="2" face="Arial">With the end points and the links chosen, the necessary bandwidth can
be estimated. Traffic on the links may have varying requirements for
latency and jitter. With the bandwidth availability already
determined, suitable link technologies must be selected. </font></p>
<p><font size="2" face="Arial">Finally, installation and operational costs for the WAN can be
determined and compared with the business need driving the WAN
provision.</font></p>
<p><font size="2" face="Arial">In practice, following the steps shown in
Figure <img border="0" src="../../images/3.gif" align="absmiddle" width="12" height="12"> is seldom a linear
process. Several modifications may be necessary before a design is
finalized. Continued monitoring and re-evaluation are also required
after installation of the WAN to maintain optimal performance.</font></p>
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<p><font color="#808080">
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<p>Drag and Drop: WAN Design Steps</p>
<p>When the student has completed this activity, the student
will be able to identify the basic steps in designing a WAN.</p>
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