Allied Telesis AT-WR4600 User Manual

How To | Configure the WLAN with QoS

Introduction

This How to Note explains how to configure Quality of Service (QoS) in a wireless
Local Area Network to prioritize traffic under busy conditions.

There is an example scenario provided at the end of this document, which
describes the configuration for prioritizing voice traffic. This example could be
extended to cover a wider installation case.

For a complete description of the commands used in this document, please refer
to the following guide:

“AT-WR4600 Series – Command Reference Guide”.

PN 613-001665 Rev. A alliedtelesis.com

Ethernet™ is a tradem ark of Xerox Corporation.

Wi-Fi®, Wi-Fi Alliance®, WMM®, Wi-Fi Protected Access® (WPA), the Wi-Fi CERTIFIED logo,
the Wi-Fi logo, the Wi-Fi ZONE logo and the Wi-Fi Protected Setup logo are registered
trademarks of the Wi-Fi Alliance. Wi-Fi CERTIFIED™, Wi-Fi Direct™, Wi-Fi Protected Setup™,
Wi-Fi Multimedia™, WPA2™, Pass point™, and the Wi-Fi Alliance logo are trademarks of the
Wi-Fi Alliance

UPnP™ is a certification mark of the UPnP™ Implementers Corporation.

Microsoft®, MS-DOS®, Windows®, Windows NT® and Windows Vista® are either registered
trademarks or trademarks of Microsoft Corporation in the United States and/or other countries.

Other brands and product names may be trademarks or registered trademarks of their
respective holders. All other logos, trademarks and service marks are the property of their
respective owners, where marked or not.

Product

Software
Version

Description and Notes

AT-WR4662n

1.1 b248 onward

High-Speed Mobility – Wireless base router

IEEE 802.11a/b/g/n dual radio, 2x2 MIMO

AT-WR4652-80

1.1 b248 onward

High-Speed Mobility – Wireless mobile router

IEEE 802.11a/b/g/n dual radio, 1x1 MIMO

AT-TQ00xx

Cables and accessories

Note: Selection is application-dependent

AT-6101G

IEEE 802.3af Gigabit Ethernet PoE Injector

Note: Use it to inter-connect AT-WR4662n

Trademarks

The following trademarks appear in this document:

Which products and software version does this
document apply to?

This document applies to the following Allied Telesis products:

Table 1 – Allied Telesis network products

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Table of contents

Introduction ...................................................................................................................................................... 1

Trademarks........................................................................................................................................................ 2

Which products and software version does this document apply to?................................................... 2

Table of contents.............................................................................................................................................. 3

Overview ........................................................................................................................................................... 4

What is Wi-Fi Multimedia (WMM) ............................................................................................................... 4

Why use Wi-Fi Multimedia? ........................................................................................................................... 4

How Wi-Fi Multimedia works........................................................................................................................ 5

How to configure Wi-Fi Multimedia ............................................................................................................. 7

Parameter descriptions................................................................................................................................... 7

Connecting AT-WR4600 products ................................................................................................................ 8

Configuration example.................................................................................................................................. 10

Using QoS to prioritize voice traffic ...................................................................... 10

Common setup ................................................................................................... 11

[Bridge0] station role: root bridge ................................ ......................................... 12

[Bridge1] station role: non-root bridge [AP1] station role: root access-point........... 13

[Bridge2] station role: non-root bridge................................................................... 14

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Overview

What is Wi-Fi Multimedia (WMM)

The Wi-Fi Alliance defined WMM as a subset of the IEEE 802.11e standard to
support QoS on wireless networks. WMM offers a mechanism to prioritize traffic
demands from different applications and grants an adequate support to
multimedia applications, thereby reducing the harmful effects caused by high
latency and throughput reductions.

Why use Wi-Fi Multimedia?

Multimedia and data-centric applications typically share the same network
resources, despite their conflicting requirements for data delivery. Without QoS,
the network offers a best-effort service, which means that applications have equal
opportunities to transfer data. WMM enables network managers to prioritize traffic
based on bandwidth requirements, especially delay-sensitive applications such as
Voice over Wireless LAN and streaming multimedia.

QoS policies play a key role when traffic load exceeds the capability of network
resources, or when some applications, like file transfers, consume the available
bandwidth. Based on services classification, WMM individually manages the
traffic classes to provide low latency, reliability, and a more predictable delay to
critical services.

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How Wi-Fi Multimedia works

In the IEEE 802.11 standard, the wireless nodes access the medium using the
“listen-before-talk” algorithm CSMA/CA-based 1 Distributed Coordination Function
(DCF). The wireless node transmits a frame once its checks indicate that the
medium is free for a period of distributed inter-frame space (DIFS) and a random
back-off time has elapsed. Otherwise, it defers the frame delivery. Note that
contention reduces the available bandwidth, because nodes must back off before
retrying to communicate.

DCF offers an efficient mechanism for transferring bursty traffic, but all nodes use
the same access method, consequently a real time data source will face
continuous contention with a large data transfer happening at the same time.

WMM provides two features that resolve contention and enable QoS:

 Enhanced Distributed Channel Access (EDCA)
 Hybrid Controlled Channel Access (HCCA)2

EDCA gives precedence to higher-priority traffic by means of a shorter arbitration
interframe space (AIFS) and contention windows (CW). The back off time is the
sum of predefined AIFS and a random value from 0 to CW, which is doubled at
each collision till the limit (CW

) is reached. Figure 1depicts the timing. In

max

addition, transmit opportunity (TXOP) bounds the time allocated to the node for
data delivery.

HCCA is a centralized access control facility coordinated by the access point,
which acts as point coordinator (PC). The PC collects the status of registered
stations (via polling) and provides them the permission for channel occupancy
and assigns, for example, the TXOP, the transmit start time and duration.

1 Carrier Sense Multiple Access with Collision Avoidance.

2 HCCA facility is not delivered by current software release.

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