Why Do I Need LLQ on My Network?
You should consider using LLQ if you need to provide good QoS to delay- and
jitter-sensitive applications like VoIP. Because LLQ is an extension of CBWFQ, it
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complements network designs that are already using CBWFQ to give differential
services to classes of applications.You have only to configure another class and
designate it as “priority” with an appropriate bandwidth limitation to give low
latency service to your real-time applications.
Because LLQ is an extension of CBWFQ, you also have access to all the
matching criteria that is provided normally to CBWFQ.This is in contrast to
RTP priority queuing, which limits match criteria to a UDP port range. Since
one of these matching criteria is IP precedence, the DiffServ model can be leveraged
to use packet marking at edge devices and allow CBWFQ with LLQ to
give low latency service to designated packets without long ACLs.This speeds up
packet processing time and overall performance. LLQ is also more flexible than
RTP priority queuing in that it can be enabled on ATM virtual circuits (VCs) to
allow timely de-queuing of delay-sensitive traffic into ATM networks.
Finally, the hard limit of the bandwidth for priority classes acts as a sort of
traffic cop that prevents LLQ from starving other traffic classes of bandwidth in
congested situations.