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.

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.

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.

For each pair of end points and for each traffic type, information is needed on the various traffic characteristics. 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.

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.

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.

Finally, installation and operational costs for the WAN can be determined and compared with the business need driving the WAN provision.

In practice, following the steps shown in Figure 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.

Interactive Media Activity Drag and Drop: WAN Design Steps When the student has completed this activity, the student will be able to identify the basic steps in designing a WAN.