WESM zl Management and Configuration Guide WT.01.28 and greater

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Wireless Local Area Networks (WLANs)
Traffic Management (QoS)
The Wireless Edge Services zl 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
3 Video
4 Voice