H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 709)

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Configuring wireless QoS
Overview
An 802.11 network offers wireless access based on the carrier sense multiple access with collision
avoidance (CSMA/CA) channel contention. All clients accessing the WLAN have equal channel
contention opportunities. All applications carried on the WLAN use the same channel contention
parameters. A live WLAN, however, is required to provide differentiated access services to address
diversified requirements of applications for bandwidth, delay, and jitter.
When IEEE 802.11e was being standardized, Wi-Fi Alliance defined the Wi-Fi Multimedia (WMM)
standard to allow QoS provision devices of different vendors to interoperate. WMM makes a WLAN
network capable of providing QoS services.
Terminology
WMM
WMM is a wireless QoS protocol designed to preferentially transmit packets with high priority, and
guarantees better QoS services for voice and video applications in a wireless network.
EDCA
Enhanced distributed channel access (EDCA) is a channel contention mechanism designed by WMM to
preferentially transmit packets with high priority and allocate more bandwidth to such packets.
AC
WMM uses access categories (ACs) for handling channel contentions. WMM assigns WLAN data to
four access categories: AC-VO (voice), AC-VI (video), AC-BE (best-effort), and AC-BK (background), in
the descending order of priority. Each access category uses an independent priority queue for
transmitting data. When contention occurs, WMM guarantees that a high-priority access category
preempts a low-priority access category.
CAC
Connection admission control (CAC) limits the number of clients that are using high-priority access
categories (AC-VO and AC-VI) to guarantee sufficient bandwidth for existing high-priority traffic.
U-APSD
Unscheduled automatic power-save delivery (U-APSD) is a new power saving mechanism defined by
WMM to enhance the power saving capability of clients.
SVP
SpectraLink voice priority (SVP) is a voice priority protocol designed by the Spectralink company to
guarantee QoS for voice traffic.