网络性能的测量-----外文翻译.docVIP

英文翻译：本文出自《Computer Network》第四版 Andrew S.Tanenbaum　著　 Network Performance Measurement When a network performs poorly, its users often complain to the folks running it, demanding improvements. To improve the performance, the operators must first determine exactly what is going on. To find out what is really happening, the operators must make measurements. In this section we will look at network performance measurements. The discussion below is based on the work of Mogul (1993). The basic loop used to improve network performance contains the following steps: Measure the relevant network parameters and performance. Try to understand what is going on. Change one parameter. These steps are repeated until the performance is good enough or it is clear that the last drop of improvement has been squeezed out. Measurements can be made in many ways and at many locations (both physically and in the protocol stack). The most basic kind of measurement is to start a timer when beginning some activity and see how long that activity takes. For example, knowing how long it takes for a TPDU to be acknowledged is a key measurement. Other measurements are made with counters that record how often some event has happened (e.g., number of lost TPDUS). Finally, one is often interested in knowing the amount of something, such as the number of bytes processed in a certain time interval. Measuring network performance and parameters has many potential pitfalls. Below we list a few of them. Any systematic attempt to measure network performance should be careful to avoid these. Make Sure That the Sample Size Is Large Enough Do not measure the time to send one TPDU, but repeat the measurement, say, one million times and take the average. Having a large sample will reduce the uncertainty in the measured mean and standard deviation. This uncertainty can be computed using standard statistical formulas. Make Sure That the Samples Are Representative Ideally, the whole sequence of one million measuremen