Wireless/Redundant Edge Services xl Module Management and Configuration Guide WS.01.03 or greater

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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, the lower the latency for
traffic in the queue, and in a congested network, the higher the
throughput. In a congested network, raising the AIFSN or the CW
minimum of low-priority queues can improve QoS for high-priority.
Raising the AIFSN a certain amount sometimes has a more dramatic
effect than raising the CW the same amount. However, raising either
too high can starve out low-priority traffic.
• By default, high-priority queues on the RP use an AIFSN of 1 ms; high-
priority queues on stations, one 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
65535, 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
Maximum values can decrease the number of collisions.
• The CW Maximum must always be higher than the CW Minimum.
6. Select the prioritization protocol used in your Ethernet network:
• 802.1p is a Layer 2 protocol that marks traffic for one of eight priorities
in the VLAN tag.
• DSCP is a Layer 3 protocol that marks traffic for one of 64 priorities
in the IP header.
Wireless devices place frames in a queue according to the priority marked
by the selected protocol. For example, if you select 802.1p, a wireless
devices transmits a frame with priority value 5 in its VLAN tag, using the
parameters in WMM queue 3. A frame with a DSCP value in the IP header,
but no 802.1p value, is transmitted in the queue for default traffic.
Refer to Table 3-6 on page 3-75 to review to which WMM queues various
priorities map.