WAN Design

This section describes the WAN design methodology and the application and technical requirement aspects of WAN design. The different possibilities for WAN ownership are discussed.

WAN bandwidth optimization techniques are described.

The methodology espoused here follows the guidelines of the Prepare-Plan-Design-Implement-

Operate-Optimize (PPDIOO) methodology introduced in Chapter 2, "Applying a Methodology to

Network Design." The network designer should follow these steps when planning and designing the Enterprise Edge based on the PPDIOO methodology:

Step 1 Analyzing customer requirements: The initial step in the design methodology is to analyze the requirements of the network and its users, including the type of applications, the traffic volume, and traffic patterns. User needs continually change in response to changing business conditions and changing technology. For example, as more voice and video-based network applications become available, there is pressure to increase network bandwidth.

Step 2 Characterizing the existing network and sites: The second step is to analyze the existing networking infrastructure and sites, including the technology used and the location of hosts, servers, terminals, and other end nodes. Together with the network's physical description, the analysis should evaluate the possibility of extending the network to support new sites, new features, or the reallocation of existing nodes. For example, the future integration of data and telephone systems requires considerable changes in the network's configuration. In this case, a detailed evaluation of current options is important.

Step 3 Designing the network topology and solutions: The final step in the design methodology is to develop the overall network topology and its appropriate services, based on the availability of technology, and taking into account the projected traffic pattern, technology performance constraints, and network reliability. The design document describes a set of discrete functions performed by the Enterprise Edge modules and the expected level of service provided by each selected technology, as dictated by the SP.

Planning and designing WAN networks involves a number of trade-offs, including the following:

■ Application aspects of the requirements driven by the performance analysis

■ Technical aspects of the requirements dealing with the geographic regulations and the effectiveness of the selected technology

■ Cost aspects of the requirements; costs include those of the equipment and of the owned or leased media or communication channel

NOTE WAN connections are typically characterized by the cost of leasing WAN infrastructure and transmission media from an SP. WAN designs must therefore trade off between the cost of bandwidth and the bandwidth efficiency.

The network's design should also be adaptable for the inclusion of future technologies and should not include any design elements that limit the adoption of new technologies as they become available. There might be trade-offs between these considerations and cost throughout the network design and implementation. For example, many new internetworks are rapidly adopting VoIP technology. Network designs should be able to support this technology without requiring a substantial upgrade by provisioning hardware and software that have options for expansion and upgradeability.

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