网络性能的测量

网络性能的测量
当一个网络的运行效果很差的时候，它的用户通常会向网络运行商抱怨并要求提高网络的质量。为了改善网络的性能，网络操作人员首先必须确定发生了什么问题。为了找出真正的问题所在，操作人员必须进行测量工作。在这一小节中，我们来看一看网络性能的测量问题。下面的讨论以Mogul(1993)的工作为基础。
用来改善网络性能的基本循环过程包括以下步骤：
（1） 测量有关的网络参数和性能。(毕业设计)
（2） 试图理解当前的网络状况。
（3） 改变一个参数。
这些步骤不断重复，直到网络的性能已经足够好，或者改善性能的全部空间都已经被发掘出来了。
测量工作可以有许多做法，也可以在许多地点或场所进行（既指物理位置，也指协议栈中的位置）。最基本的一种测量手段是：在开始某一个动作的时候启动一个定时器，然后确定该需要多长时间。例如，知道一个TPDU需要多长时间才被确认是一个很关键的测量指标。其他有一些测量指标可以通过计数器来完成，即记录某种事件发生的次数，比如丢失的TPDU的数量。最后，人们通常对于某些事物的数量比较感兴趣，比如在特定的时间间隔内所处理的字节数。
测量网络的性能和参数有许多潜在的陷阱。以下我们列出其中一部分。任何一种系统化的网络性能测量手段都应该小心地避免这些陷阱。

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:
1. Measure the relevant network parameters and performance.
2. Try to understand what is going on.
3. 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.

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