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Developing a Baseline of Network Performance

Developing an accurate baseline of a network's performance is not an easy task. One challenging aspect is selecting a time to do the analysis. It is important that you allocate a lot of time (multiple days) if you want the baseline to be accurate. If measurements are made over too short a timeframe, temporary errors appear more significant than they are.

In addition to allocating sufficient time for a baseline analysis, it is also important to find a typical time period to do the analysis. A baseline of normal performance should not include nontypical problems caused by exceptionally large traffic loads. For example, at some companies, end-of-the quarter sales processing puts an abnormal load on the network. In a retail environment, network traffic can increase fivefold around Christmas time. Network traffic to a web server can unexpectedly increase tenfold if the website gets linked to other popular sites or listed in search engines.

In general, errors, packet/cell loss, and latency increase with load. To get a meaningful measurement of typical accuracy and delay, try to do your baseline analysis during periods of normal traffic load. (On the other hand, if your customer's main goal is to improve performance during peak load, then be sure to study performance during peak load. The decision whether to measure normal performance, performance during peak load, or both, depends on the goals of the network design.)

Some customers do not recognize the value of studying the existing network before designing and implementing enhancements. Your customer's expectations for a speedy design proposal might make it difficult for you to take a step back and insist on time to develop a baseline of performance on the existing network. Also, your other job tasks and goals, especially if you are a sales engineer, might make it impractical to spend days developing a precise baseline.

The work you do before the baseline step in the top-down network design methodology can increase your efficiency in developing a baseline. A good understanding of your customer's technical and business goals can help you decide how thorough to make your study. Your discussions with your customer on business goals can help you identify segments that are important to study because they carry critical and/or backbone traffic. You can also ask your customer to help you identify typical segments from which you can extrapolate other segments.