外文翻譯--網(wǎng)絡(luò)性能的測(cè)量-文庫(kù)吧
2025-04-17 06:02 本頁(yè)面
【正文】 ion times and take the average. Having a large sample will reduce the uncertainty in the measured mean and standard deviation. This uncertainty can be puted using standard statistical formulas. Make Sure That the Samples Are Representative Ideally, the whole sequence of one million measurements should be repeated at different times of the day and the week to see the effect of different system loads on the measured quantity. Measurements of congestion, for example, are of little use if they are made at a moment when there is no congestion. Sometimes the results may be counterintuitive at first, such as heavy congestion at 10, 11, 1, and 2 o39。clock, but no congestion at noon (when all the users are away at lunch). Be Careful When Using a CoarseGrained Clock Computer clocks work by incrementing some counter at regular intervals. For example, a millisecond timer adds 1 to a counter every 1 msec. Using such a timer to measure an event that takes less than 1 msec is possible, but requires some care. (Some puters have more accurate clocks, of course.) To measure the time to send a TPDU, for example, the system clock (say, in milliseconds) should be read out when the transport layer code is entered and again when it is exited. If the true TPDU send time is 300 181。sec, the difference between the two readings will be either 0 or 1, both wrong. However, if the measurement is repeated one million times and the total of all measurements added up and divided by one million, the mean time will be accurate to better than 1 181。sec. Be Sure That Nothing Unexpected Is Going On during Your Tests Making measurements on a university system the day some major lab project has to be turned
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