Congestion due to Over-utilization
Congestion due to over-utilization happens when a switch receives more traffic destined for a specific link than the capacity of that link. The link transmits at its full capacity and its remaining-Tx-B2B-credits don’t fall to zero. To equalize the ingress frame rate with the egress frame rate, the switch reduces the rate of sending the R_RDYs to the directly attached neighbor(s) in the direction of upstream traffic. Once the directly attached neighbor(s) has zero remaining-Tx-B2B-credits they must stop sending frames. When they stop sending, in turn, they stop accepting frames from their upstream neighbor(s) causing backpressure that spreads in the direction of the ultimate source of the frames. Although the end-to-end backpressure to equalize the traffic rate is expected behavior, it adversely affects other traffic that shares the same network path. This effect is similar as caused by slow-drain. 当交换机接收到的发送到特定链路的流量超过该链路的容量时，就会出现因过度使用而造成的拥塞。链路以其全部容量进行传输，而其剩余的 Tx-B2B 信元不会降为零。为了使入口帧速率与出口帧速率相等，交换机会降低向上游流量方向的直连邻居发送 R_RDY 的速率。一旦直连邻居的剩余 Tx-B2B 信元为零，它们就必须停止发送帧。当它们停止发送时，反过来也会停止接受来自上游邻居的帧，从而造成向帧最终来源方向扩散的反向压力。尽管端到端反向压力使流量速率均衡是意料之中的行为，但它会对共享相同网络路径的其他流量产生不利影响。这种影响与慢排空造成的影响类似。
A high-level overview of over-utilization and its reasons are explained in Chapter 1, the section on Congestion Due to Over-Utilization of a Link. This section expands on the same details with a focus on host-edge links because this is the most widely reported condition in production Fibre Channel fabrics, although congestion due to over-utilization can happen on any link in a fabric. Over-utilization on an ISL is explained in a later section. 第 1 章 "链路过度使用导致的拥塞 "一节对过度使用及其原因进行了高级概述。本节以主机边缘链路为重点，对相同的细节进行了阐述，因为这是生产光纤通道 Fabric 中报告最多的情况，不过 Fabric 中的任何链路都可能发生因过度使用而导致的拥塞。ISL 上的过度使用将在后面的章节中解释。
Congestion due to Over-Utilization on Host-edge Links
Congestion due to over-utilization on host links happens when hosts have requested more data from their targets than can be sent on the host-edge link. 当主机从其目标请求的数据超过主机-边缘链路可发送的数据时，主机链路上就会出现因过度使用而导致的拥塞。
Consider the example of Figure 2-14, which shows a part of an edge-core Fibr