Radio Qos Policy - Motorola Solutions WiNG 5.2.6 Reference Manual

6 - 60 WiNG 5.2.6 Access Point System Reference Guide

6.3 Radio QoS Policy

Without a dedicated QoS policy, a network operates on a best-effort delivery basis, meaning all traffic has equal
priority and an equal chance of being delivered in a timely manner. When congestion occurs, all traffic has an equal
chance of being dropped!
When configuring a QoS policy for a radio, select specific network traffic, prioritize it, and use
congestion-management and congestion-avoidance techniques to provide deployment cusomizations best suited to
each QoS policy's intended wireless client base.
Motorola Solutions Access Point radios and wireless 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, Email 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 high 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
Within a Motorola Solutions wireless network, wireless clients supporting low and high priority traffic contend with
one another for 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 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 improve 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. An
access point managed 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 WLAN
to benefit.
WMM includes advanced parameters (CWMin, CWMax, AIFSN and TXOP) specifing 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.
Access points support static QoS mechanisms per WLAN to provide prioritization of WLAN traffic when legacy (non
WMM) clients are deployed. An access point allows flexible WLAN mapping with a static WMM access control