计网第一章Delay, Loss, and Throughput in Packet-Switched Networks

Delay, Loss, and Throughput in Packet-Switched Networks

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delay

As a packet travels from one node (host or router) to the subsequent node (host or router) along this path, the
packet suffers from several types of delays at each node along the path.
The most important of these delays are the nodal processing delay, queuing delay, transmission delay, and propagation delay

1. Processing Delay：检查数据包的标头并确定将数据包定向到何处所需的时间是处理延迟的一部分。

2. queuing delay：在队列中，数据包在等待传输到链路时会遇到排队延迟。特定数据包的排队延迟长度将取决于排队并等待传输到链路上的较早到达的数据包的数量。如果队列为空，并且当前没有其他数据包正在传输，则数据包的排队延迟将为零。另一方面，如果流量很大，并且还有许多其他数据包正在等待传输，则排队延迟会很长。
   R is the transmission rate; that is, it is the rate (in bits/sec) at which bits are pushed out of the queue.
   Also suppose, for simplicity, that all packets consist of L bits.
   Then the average rate