Brocade Mobility RFS Controller System Reference Guide (Supporting software release 5.5.0.0 and later) - Manual (Page 320)

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Brocade wireless devices, associated Access Point radios and connected clients support several
Quality of Service (QoS) techniques enabling real-time applications (such as voice and video) to
co-exist simultaneously with lower priority background applications (such as Web, E-mail and file
transfers). A well designed QoS policy should:
• Classify and mark data traffic to accurately prioritize and segregate it (by access category)
throughout the network.
• Minimize the network delay and jitter for latency sensitive traffic.
• Ensure higher priority traffic has a better likelihood of delivery in the event of network
congestion.
• Prevent the ineffective utilization of Access Points degrading session quality by configuring
admission control mechanisms within each radio QoS policy
Wireless clients supporting low and high priority traffic contend with one another for access and
data resources. The IEEE 802.11e amendment has defined Enhanced Distributed Channel Access
(EDCA) mechanisms stating high priority traffic can access the network sooner then lower priority
traffic. The EDCA defines four traffic classes (or access categories); voice (highest), video (next
highest), best effort and background (lowest).The EDCA has defined a time interval for each traffic
class, known as the Transmit Opportunity (TXOP). The TXOP prevents traffic of a higher priority from
completely dominating the wireless medium, thus ensuring lower priority traffic is still supported by
controller or service platform associated Access Points and their connected radios.
IEEE 802.11e includes an advanced power saving technique called Unscheduled Automatic Power
Save Delivery (U-APSD) that provides a mechanism for wireless clients to retrieve packets buffered
by an Access Point. U-APSD reduces the amount of signaling frames sent from a client to retrieve
buffered data from an Access Point. U-APSD also allows Access Points to deliver buffered data
frames as bursts, without backing-off between data frames. These improvements are useful for
voice clients, as they provide improved battery life and call quality.
The Wi-Fi alliance has created Wireless Multimedia (WMM) and WMM Power Save (WMM-PS)
certification programs to ensure interoperability between 802.11e WLAN infrastructure
implementations and wireless clients. A Brocade wireless network supports both WMM and
WMM-Power Save techniques. WMM and WMM-PS (U-APSD) are enabled by default in each WLAN
profile.
Enabling WMM support on a WLAN just advertises the WLAN’s WMM capability and radio
configuration to wireless clients. The wireless clients must be also able to support WMM and use
the values correctly while accessing the WLAN.
WMM includes advanced parameters (CWMin, CWMax, AIFSN and TXOP) specifying back-off
duration and inter-frame spacing when accessing the network. These parameters are relevant to
both connected Access Point radios and their wireless clients. Parameters impacting Access Point
transmissions to their clients are controlled using per radio WMM settings, while parameters used
by wireless clients are controlled by a WLAN’s WMM settings.
Brocade wireless devices include a Session Initiation Protocol (SIP), Skinny Call Control Protocol
(SCCP) and Application Layer Gateway (ALGs) enabling devices to identify voice streams and
dynamically set voice call bandwidth. Controllers and service platforms use the data to provide
prioritization and admission control to these devices without requiring TSPEC or WMM client
support.
Brocade wireless devices support static QoS mechanisms per WLAN to provide prioritization of
WLAN traffic when legacy (non WMM) clients are deployed. When enabled on a WLAN, traffic
forwarded to a client is prioritized and forwarded based on the WLAN’s WMM access control
setting.