Wlan Qos Features Supported By The Spu - Huawei quidway s7700 Configuration Manual

Quidway S7700 Smart Routing Switch
Configuration Guide - SPU
An 802.11 network provides the competition-based wireless access service. Different
applications have different requirements for networks; however, traditional networks cannot
provide access services of different qualities for different applications.
IEEE 802.11e defines the QoS feature for the 802.11-based WLAN system. The Wi-Fi Alliance
defines the Wi-Fi Multimedia (WMM) standard for communication between QoS-supported
devices of different WLAN vendors. WMM enables a WLAN network to provide QoS features.
WMM
WMM provides QoS features for 802.11 networks and enables high-priority packets to be sent
first, providing better quality for voice and video services on WLANs.
EDCA
Enhanced Distributed Channel Access (EDCA) is a channel preemption mechanism defined by
WMM, enabling high-priority packets to be sent first and allocated more bandwidth.
AC
WMM prioritizes queues of four access categories (ACs) in descending order, that is, AC-voice
(AC-VO), AC-video (AC-VI), AC-best effort (AC-BE), and AC-background (AC-BK). This
ensures that packets in a high-priority queue have greater capabilities in channel preemption.

5.3.2 WLAN QoS Features Supported by the SPU

The SPU supports radio QoS policy management, VAP QoS policy management, and user
priority and CAR management.
Radio QoS Policy Management
In the 802.11 protocol, the distributed coordination function (DCF) defines the Carrier Sense
Multiple Access with Collision Avoidance (CSMA/CA) access mechanism for APs and STAs.
Before occupying a channel to send packets, APs or STAs monitor the channel. If the channel
idle time is longer than or equal to the arbitration inter frame spacing number (AIFSN), each
AP or STA selects a random backoff time between exponent form of minimum contention
window (ECWmin) and exponent form of maximum contention window (ECWmax). The AP
or STA whose backoff timer expires the first occupies the channel and starts to send packets
over the channel.
WMM provides four AC queues (AC-VO, AC-VI, AC-BE, and AC-BK) for data packets,
allowing packets in a high-priority AC queue to have greater capabilities in channel preemption.
A set of EDCA parameters is set for each AC queue. These parameters determine the capabilities
of queues in channel preemption.
EDCA parameters are as follows:
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AIFSN: determines the channel idle time. A greater AIFSN value indicates a longer channel
idle time.
ECWmin and ECWmax: determine the average backoff time. A greater value indicates a
longer average backoff time.
Transmission opportunity limit (TXOPLimit): determines the maximum duration in which
an AP or a STA can occupy a channel. A greater TXOPLimit value indicates a longer
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