WESM zl Management and Configuration Guide WT.01.28 and greater

4-103
Wireless Local Area Networks (WLANs)
Traffic Management (QoS)
Again, take great care in establishing these settings. ProCurve Networking
cannot guarantee any behavior. However, you can keep these tips in mind:
• The lower the AIFSN and the CW minimum values, the lower the latency
for traffic in the queue, and in a congested network, the higher the through-
put. In a congested network, raising the AIFSN or the CW minimum of low-
priority queues can improve QoS for high-priority. Raising the AIFSN value
a certain amount sometimes has a more dramatic effect than raising the CW
value the same amount. However, raising either value too high can starve
out low-priority traffic.
• By default, high-priority queues on the RP use an AIFSN value of 1 ms;
high-priority queues on stations use an AIFSN value of 2 ms. You might
want to reserve the 1-ms AIFSN for RPs.
• When you grant a queue a Transmit Ops, you allow a station that wins access
to the radio continued access to the medium for that length of time. If you
set this value excessively high, then lower-priority traffic, and even other
high-priority traffic, may be unacceptably delayed. Although the Web
browser interface lists the maximum value as 65,535, generally the Transmit
Ops is set in terms of tens, or at the most, hundreds of milliseconds—not
thousands. In several seconds, applications can time out, frustrating users
throughout your network.
• In a network with many users and high congestion, increasing CW Maxi-
mum values can decrease the number of collisions.
• The CW Maximum value must always be higher than the CW Minimum
value.
Viewing and Customizing RP WMM Parameters
As discussed earlier, RPs handle traffic as dictated by the WMM parameters (AISFN
and so forth) for the traffic’s AC. Also as discussed earlier, the Wireless Edge Services
zl Module assigns traffic to an AC according to the WLAN setting or, if the AC is
set to automatic/WMM, according to priority value.
The ProCurve 210, 220, and 230 RPs use default parameters that work for nearly all
applications. (For example, the parameters are such that voice frames more quickly
and more often win access to the medium.)
Note Because the Wireless Edge Services zl Module automatically defines settings such
that traffic in a higher-priority queue receives lower latency, the default radio WMM
settings are usually adequate. Incorrect settings can adversely affect network perfor-
mance; ProCurve Networking strongly recommends that you do not change these
parameters.