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3.2 | The First Steps in WAN Design |
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3.2.3 | Analyzing requirements |
You need to analyze network
requirements, including the customer's business and technical goals.
What new applications will be implemented? Are any applications
Internet based? What new networks will be accessed? What are the
success criteria? (How will you know if the new design is successful?)
Availability measures the usefulness of the network. Many things affect availability, including throughput, response time, and access to resources. Every customer has a different definition of availability. You can increase availability by adding more resources. Resources drive up cost. Network design seeks to provide the greatest availability for the least cost. The objective of analyzing requirements is to determine, the average and peak data rates for each source over time. Try to characterize activity throughout a normal work day in terms of the type of traffic passed, level of traffic, response time of hosts, and the time to execute file transfers.
You can also
observe utilization on existing network equipment over the test
period. If the tested network's characteristics are close to those of the new network, you can estimate the new network's requirements based on the projected number of users, applications, and topology. This is a best-guess approach to traffic estimation given the lack of tools to measure detailed traffic behavior. In addition to passively monitoring an existing network, you can measure activity and traffic generated by a known number of users attached to a representative test network and then calculate findings to your anticipated population. One problem with defining workloads on networks is that it is difficult to accurately pinpoint traffic load and network device performance as functions of the number of users, type of application, and geographic location. This is especially true without a real network in place. Consider the following factors that influence the dynamics of the network:
Each traffic source has its own metric, and each must be converted to bits per second. You should standardize traffic volumes to obtain per-user volumes. Finally, you should apply a factor to account for protocol overhead, packet fragmentation, traffic growth, and safety margin. By varying this factor, you can conduct what-if analyses. For example, you could run Microsoft Office from a server, and then analyze the traffic volume generated from users sharing the application on the network. This volume will help you determine the bandwidth and server requirements to install Microsoft Office on the network.
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