Congestion in Single-switch Fabrics
Contrary to common belief, congestion affects single switch Fibre Channel fabrics also, although the number of affected devices in a single-switch fabric is fewer as compared to multi-switch fabric (edge-core and edge-core-edge fabrics) where thousands of end-devices share the network paths. 与通常的看法相反，拥塞也会影响单交换机光纤通道 Fabric，尽管与多交换机 Fabric（边缘-核心和边缘-核心-边缘 Fabric）相比，单交换机 Fabric 中受影响的设备数量较少，因为在多交换机 Fabric 中，成千上万的终端设备共享网络路径。
Consider the example in Figure 2-19 to understand the effect of congestion in a single switch fabric. Host-1 receives traffic from Target-1, while Host-2 receives traffic from Target-2. 请参考图 2-19 中的示例，了解单个交换机 Fabric 中拥塞的影响。主机-1 接收来自目标-1 的流量，而主机-2 接收来自目标-2 的流量。
Figure 2-19 Congestion in a single-switch fabric
If Host-1 becomes a slow-drain device (reduces the rate of sending of R_RDY), the remaining-Tx-B2B-credits fall to zero on Port-1, and therefore Port-3 can’t switch frames to Port-1. Consequently, Port-3 reduces the rate of sending of R_RDYs to Target-1. Overall, the traffic from Port-1 to Host-1 and Target-1 to Port-3 is affected. But the traffic from Port-2 to Host-2 and Target-2 to Port-4 is unaffected. This is how a single switch fabric reduces the spread of congestion. 如果主机-1 成为慢排空设备（降低 R_RDY 发送速率），端口-1 上剩余的 Tx-B2B
