Dell 6.2 Configuring Dynamic WMM Queue Management

any destination [LYNC_SERVER] [LYNC_PORTS] permit tos 44 dot1p-priority 6
any destination [SCOPiA_SERVER] [SCOPIA _PORTS] permit tos 42 dot1p-priority 6
NOTE:You m ustknow the ports on which each traffic is sent so thatthe correct traffic is identified.
Configuring Dynamic WMM Queue Management
Traditional wireless networks provide all clients with equal bandwidth access. However, delays or reductions in
throughputcan adversely affect voice and video applications, resultingi n disruptedV oIP conversations or dropped
framesi n a streamedvi deo. Thus,data streams that requirest rict latency and throughputneed to be assigned higher
traffic priority than othertraffic types.
The Wi-FiA lliancedefined the Wi-Fi Multimedia(WMM) standard in responset o industryrequirements for
Quality of Service (QoS) support for multimediaapplicati ons for wireless networks. This is defined as per the IEEE
802.11e standards.
WMMrequires:
lThe access point is Wi-Fi Certified and has WMM enabled
lThe client device is Wi-Fi Certified
lThe application supports WMM
EnhancedDistributed ChannelAccess
WMMprovides media access prioritization through Enhanced Distributed Channel Access (EDCA ). EDCA defines
fouraccess categories (ACs) to prioritize t raffic:voi ce, video, best effort, andbackground. These ACs correspond to
802.1p priority tags, as shown in Table 302 .
WMM Access Category Description 802.1p Tag
Voice Highestpriority 7,6
Video Prioritize video traffic above otherdata traffic 5,4
BestEffort Trafficfrom l egacy devices or traffic from applications or devices that
donot support QoS
0,3
Background Lowpri oritytraffic (file downloads, print jobs) 2,1
Table30 2: WMMA ccess Categories and802.1p Tags
Whilethe WMM ACs designate specific t ypes of traffic,yo ucan determine the priority of the ACs. For example,
you can choose to give video trafficthe highest priority. With WMM, applications assign data packetst o anAC. In
the client, thedat a packets arethen added to one of the transmit queues for voice, video, best effort, or background.
WMMi s an extension to the Carrier Sense Multiple Access with Collision Avoi dance (CSMA/CA) protocol’s
Distributed Coordination Function (DCF). The collision resolution algorithm responsible for traffic prioritizati on
dependson t he followingco nfigurableparameters for each AC:
larbitraryi nter-framespace number (AIFSN)
lminimum andmaximum contention wi ndow (CW) size
For each AC, the backoffti me is the sum of the AIFSN and a randomvalue between 0 and the CW value. TheA C
with the lowest backoff time is granted the opportunity to transmit (TXOP). Frames with the highest-priority AC
are morelikely to get TXOP as they tend to have the lowest backoffti mes(a result of having smallerAIFSN and
CW parametervalues). The value of the CW varies through time as the CW doubles after each collision up to t he
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