Wireless/Redundant Edge Services xl Module Management and Configuration Guide WS.02.xx and greater

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Wireless Local Area Networks (WLANs)
Traffic Management (QoS)
Prioritization with WMM
WMM improves QoS by dividing traffic into priority queues, one for each of
four access categories (ACs). The higher the AC, the higher the QoS the traffic
requires.
The Wireless Edge Services xl Module can use WMM to prioritize the following
traffic:
■ traffic sent from RP radios to wireless stations
■ traffic sent from wireless stations to RP radios
Priority Queuing and ACs. Table 4-7 shows the ACs into which RPs and
wireless stations can divide traffic.
Table 4-7. WMM ACs
Each AC queue is defined by different parameters, which include:
■ the IFS—now called the arbitration IFS number (AIFSN)
■ the minimum contention window (CW Min)—the maximum value for the
initial random backoff time
■ the maximum contention window (CW Max)—the maximum value for the
random backoff time in a network experiencing collisions
■ the transmit opportunity (Transmit Ops)—the continuous time during
which a device that has won control of the radio can retain control
When devices use different parameters to transmit different types of traffic,
the most time-sensitive traffic can receive the QoS that it needs. For example,
the queue for voice traffic uses a smaller contention window, so VoWLAN
devices on average choose smaller backoff times and win control of the
medium more quickly.
When you enable WMM, traffic is assigned to an AC (and WMM queue)
according to its QoS mark. Table 4-8 shows how QoS marks map to ACs, by
default. You can customize these mappings for traffic transmitted by RP
radios. (See “Customizing How QoS Marks Map to ACs” on page 4-106.)
Queue Number AC
1 Background
2 Best Effort
3Video
4Voice