Chapter 1-20. Introduction to Congestion in Storage Networks

Propagation Delay

Propagation delay is the time taken by a signal to travel the length of a link. It is defined by the speed of light, which is approximately 200,000 km/s in optical media (and 300,000 km/s in vacuum). A simple way to remember it is that a signal travels 1 meter in 5 nanoseconds. In other words, a 100-meter cable causes a delay of 500 nanoseconds. 传播延迟是指信号在链路上传播所需的时间。它由光速定义，光速在光学介质中约为 20 万公里/秒（在真空中约为 30 万公里/秒）。一个简单的记忆方法是，信号在 5 纳秒内传输 1 米。换句话说，一根 100 米长的电缆会造成 500 纳秒的延迟。

In Fibre Channel networks, propagation delay is an important factor for calculating the required number of B2B credits. Refer to Chapter 2, the section on Detailed Explanation for the Required B2B Credits on an FC port. Likewise, in lossless Ethernet networks, propagation delay is used for calculating the pause thresholds and headroom. Refer to Chapter 7, the section on Pause Thresholds for Long Distance Links for more details. 在光纤通道网络中，传播延迟是计算所需 B2B 信用点数的一个重要因素。请参阅第 2 章 "FC 端口所需 B2B 信用点的详细说明 "