Queue Depth Monitoring and Microburst Detection

Queue depth monitoring and microburst detection capture the events that may cause congestion at a lower granularity but are unnoticed by other means due to long polling intervals. 队列深度监控和微爆检测可捕捉到可能导致较低粒度拥塞的事件，但由于轮询间隔较长，其他方法无法捕捉到这些事件。

Consider a link that operates at 100% utilization for 100 ms and 0% utilization for the next 900 ms. The reported link utilization during this 1-second interval is averaged to 10% utilization. As a result, this congestion event is not captured by monitoring link utilization. The following are the approaches that can detect this condition: 假设一条链路在 100 毫秒内的利用率为 100%，在接下来的 900 毫秒内的利用率为 0%。在这 1 秒间隔内报告的链路利用率平均为 10%。因此，监控链路利用率无法捕捉到这一拥塞事件。以下是可以检测到这种情况的方法：

1. Packet drop counters. But these may increment only if the queues are full (Figure 8-16). 丢包计数器。但只有当队列已满时，这些计数器才会递增（图 8-16）。

2. ECN counters, if ECN is enabled. But these may increment only if the queue utilization exceeds ECN thresholds. For example, assume that the maximum queue size is 400 KB. Packets are marked with ECN when queue utilization exceeds 100 KB. If queue utilization stays below 100 KB, the link transmits at 100% utilization for 100 ms but there would be no way to detect this condition (Figure 8-16). ECN 计数器（如果启用了 ECN）。但只有当队列利用率超过 ECN 临界值时，这些计数器才会递增。例如，假设最大队列大小为 400 KB。当队列利用率超过 100 KB 时，数据包会被标记为 ECN。如果队列利用率保持在 100 KB 以下，链路会在 100 ms 内以 100% 的利用率传输，但无法检测到这种情况（图 8-16）。

Microburst detection and queue depth monitoring capture such conditions (Figure 8-16). In the earlier example, if queue utilization is higher than 30 KB continuously for 80 microseconds, microburst detection can capture this event. 微爆检测和队列深度监控可捕获此类情况（图 8-16）。在前面的示例中，如果队列利用率在 80 微秒内连续高于 30 KB，微爆检测就能捕捉到这一事件。

Figure 8-16 Queue utilization states and their detection mechanisms

Additionally, it is possible to monitor the instantaneous utilization of the queues. Refer to Example 8-5 that shows Q Depth Byts in the command show queuing interface on Cisco Nexus 9000 switches. 此外，还可以监控队列的瞬时利用率。请参阅示例 8-5，其中显示了 Cisco Nexus 9000 交换机上显示队列接口命令中的 Q Depth Byts。