WESM zl Management and Configuration Guide WT.01.28 and greater

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Wireless Local Area Networks (WLANs)
Traffic Management (QoS)
Figure 4-52. QoS Mechanisms Supported by the Wireless Edge Services zl Module
SVP
SVP maintains a high QoS specifically for VoWLAN devices that are SVP-capable.
SVP is implemented in wireless phones, wireless APs, and SpectraLink servers. This
IEEE 802.11-compliant mechanism minimizes latency for voice traffic by providing
priority queues reserved for voice packets and by increasing the probability that all
voice packets are transmitted in a predictable and timely manner.
SVP devices access the medium without waiting the default 802.11 interframe
spacing (IFS) interval. In addition, SVP-enabled RPs and phones transmit voice
packets in a coordinated fashion, thereby eliminating the need for a random backoff
time and the attendant delays.
The Wireless Edge Services zl Module can configure RPs to support SVP—that is,
to recognize SVP frames, place them in priority queues, and transmit them with a
zero backoff time. If your network includes a SpectraLink server and SVP-capable
phones, you should enable this support in the WLAN that includes these phones.