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Quality of Service guidelines
Queuing methods
This section discusses common queuing methods and their appropriateness for voice:
WFQ
PQ
Round-robin
CB-WFQ / LLQ / CBQ
RED / WRED
WFQ
Weighted fair queuing (WFQ) is similar to first in, first out (FIFO) queuing, except that it grants a
higher weight to small flows, and flows that are marked with higher DiffServ or IP TOS priorities.
This queuing strategy does allow smaller (for example, telnet) and higher-priority (for example,
IP Telephony) protocols to squeeze in before high-flow (for example, ftp) packets, but does not
starve off any traffic. By itself, it is not appropriate for IP Telephony traffic because high-flow
traffic can still delay IP Telephony traffic, and cause unacceptable latency and jitter.
PQ
Strict priority queuing (PQ) divides traffic into different queues. These queues are usually high,
medium, normal, and low, based on traffic type. This form of queuing services the queues in
order of priority, from high to low. If there is a packet in the high-priority queue, it will always be
serviced before the queue manager services the lower-priority queues. With priority queuing,
however, it is possible to starve out lower-priority flows if sufficient traffic enters the
high-\priority queue. This mechanism works very well for IP Telephony traffic (where IP
Telephony bearer and signaling are inserted in the high-priority queue), but might work less well
for routine data traffic that is starved out if sufficient high-priority traffic arrives.
320 Avaya Application Solutions IP Telephony Deployment Guide
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