Using Low Latency Queuing
The previous section demonstrated that CBWFQ can give bandwidth guarantees
to different classes of traffic.Although CBWFQ can provide these bandwidth
guarantees, low latency transmission may not be provided to packets in congestion
situations, since all packets are transmitted fairly based on their weight.This
can cause problems for applications like VoIP that are sensitive to delays, especially
variations in delays.Variation in the delay time between individual packets that
make up a voice stream is usually referred to as jitter. Although most voice applications
can tolerate a certain amount of delay, jitter can cause choppiness in voice
transmissions and quickly degrade overall voice quality. Low Latency Queuing
(LLQ) extends CBWFQ to include the option of creating a strict priority queue.
Strict priority queuing delivers low latency transmission to constant bit rate
(CBR) applications such as voice. Due to the nature of LLQ, it is not recommended
that you configure anything other than voice traffic to be placed in the
priority queue, as this can cause serious problems for your voice traffic.
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