Severe Congestion (Level 3)
During severe congestion, an FC port triggers credit loss recovery by initiating Link Reset Protocol because it is unable to send frames for an extended duration (1 or 1.5 continuous seconds) due to credit unavailability. Link Reset Protocol involves the Link Reset (LR) and Link Reset Response (LRR) primitives. This is the most serious level of congestion. 在严重拥塞期间，FC 端口会通过启动链路重置协议（Link Reset Protocol）来触发信元丢失恢复，因为由于信元不可用，该端口在较长时间（连续 1 或 1.5 秒）内无法发送帧。链路重置协议涉及链路重置 (LR) 和链路重置响应 (LRR) 基元。这是最严重的拥塞程度。
Note that the Link Reset primitive does not actually reset the link, it just resets the B2B credits on the link. When successful, the link itself does not bounce/flap. If the Link Reset Protocol fails, it results in a link failure, which is recovered via bounce/flap. 请注意，链接重置原语实际上并不重置链接，它只是重置链接上的 B2B 信元。成功时，链路本身不会弹跳/翻转。如果链路重置协议失败，则会导致链路故障，并通过跳转/溢出恢复。
Regardless of the success of the Link Reset Protocol, the extended delay normally causes large numbers of timeout drops. Consequently, hosts report many I/O errors and aborted exchanges, and the end devices could even logout from the fabric. 无论链路重置协议是否成功，延迟延长通常都会导致大量超时掉线。因此，主机会报告许多 I/O 错误和中止的交换，终端设备甚至会从结构中注销。
Level 3 problems contain frame drops (Level 2 indications) and latency degradation (Level 1/1.5 indications like TxWait). 第 3 级问题包括丢帧（第 2