QoS and VoIP Treatment
Avaya X330WAN User’s Guide 57
VoIP Mode
The incoming packets are categorized into the Rx queues as in the Data mode.
The size of each of the four Tx queues is automatically set by X330WAN as follows:
• Highest priority queue (VoIP) - Set by default to a maximum delay of
20 milliseconds, optimized for a G.729 voice CODEC (without cRTP), and
implements tail-drop when overflowed. This queue is divided into two
priorities, 6 and 7, which are treated differently to improve distinction between
the Voice Bearer (RTP) (priority 6) and Voice Control (priority 7) packets. The
two priorities are serviced in a Round-Robin one-to-one fashion, where the
priority 6 (RTP) buffer is 25% the size of the priority 7 (Voice Control) buffer to
reduce the delay in VoIP flow. The priority 6-7 distinction exists in Data mode
as well, where the queue is divided equally between both capacities.
• The remaining queues are set using the same methods as in Data mode.
Figure 4.9 illustrates the queue and overflow concept for the Data and VoIP modes.
Figure 4.9 Default QoS Behavior
Note: You can adjust the queue length in both modes for different needs. Queue
length should always be kept as small as possible, while still maintaining a flow. It
is recommended to always use the default queue length, as this is the optimal
calculated length. To adjust the queue length in both modes, use the
queue-limit
command.
