For CBWFQ, the weight for a packet belonging to a specific class is derived from the bandwidth assigned to the class during configuration. Therefore, the bandwidth assigned to the packets of a class determines the order in which packets are sent. All packets are serviced equally, based on weight. No class of packets may be granted strict priority. This scheme poses problems for voice and video traffic that is largely intolerant of delay, especially variation in delay. For voice traffic, variations in delay introduce irregularities of transmission, which manifest as jitter in the conversation.

To enqueue a class of traffic to the strict priority queue, configure the priority command for the class after specifying the class within a policy map. Classes to which the priority command is applied are considered priority classes. Within a policy map, give one or more classes priority status. When multiple classes within a single policy map are configured as priority classes, all traffic from these classes is enqueued to the same, single, strict priority queue and they will contend with each other for bandwidth.

Although it is possible to enqueue various types of real-time traffic to the strict priority queue, Cisco recommends that only voice traffic be directed to it. This recommendation is made because voice traffic is well-behaved, whereas other types of real-time traffic are not. Moreover, voice traffic requires that delay be nonvariable in order to avoid jitter. Real-time traffic such as video could introduce variation in delay, thereby disrupting the steadiness of delay required for successful voice traffic transmission.