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.