10.2 Queuing Options
10.2.6 Custom queuing overview
Custom Queuing (CQ) lets you guarantee bandwidth for traffic by assigning queue space to each protocol. CQ eliminates a potential priority-queuing problem. When PQ is used, it is possible that packets from higher-priority queues could consume all the available interface bandwidth. As a result, packets in the lower-priority queues might not get forwarded in a timely manner, or might not get forwarded at all.

CQ eliminates this problem. With CQ, you reserve a certain percentage of bandwidth for each specified class of traffic. You can use CQ to allocate bandwidth based on a protocol or source interface.

Using CQ, you can use filters to assign types of traffic to one of 16 possible queues. The router services each queue sequentially, transmitting a configurable quantity of traffic from each queue before servicing the next queue.

As a result, one type of traffic can never monopolize the entire bandwidth. You can control the percentage of the interface bandwidth that a queue consumes by configuring the number of bytes transmitted from a queue at one time.

CQ is particularly important for time-sensitive protocols, such as voice, video, and Systems Network Architecture (SNA), which require predictable response time. Queue 0 is a system queue that handles system packets such as keepalives. Queue 0 is emptied before the other custom queues.