[1] Class-based weighted fair queuing (CB-WFQ) was initially released without the support of a priority queuing system, thus it could not guarantee the delay and jitter (delay variation) requirements of real-time, interactive voice and video conversations.
Since for CBWFQ, the weight for a packet belonging to a specific class is derived from the bandwidth assigned to the class, which in turn determines the order in which packets are sent.
In order to address this, Cisco released LLQ to provide strict priority queuing for CBWFQ by enabling the use of a single, strict priority queue within CBWFQ at the class level.
This allows for directing traffic belonging to a class to the CBWFQ strict priority queue.
One or more classes priority status can be given within a policy map.