Allied Telesis AT-WR4600 User Manual

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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-WR4600Series – Command Reference Guide”.

PN 613-001665Rev. A

alliedtelesis.com

Trademarks

The following trademarks appear in this document:

Ethernet™ is a trademark of Xerox Corporation.

Wi-Fi®,Wi-FiAlliance®, WMM®,Wi-FiProtected Access® (WPA), theWi-FiCERTIFIED logo, theWi-Filogo, theWi-FiZONE logo and theWi-FiProtected Setup logo are registered trademarks of theWi-FiAlliance.Wi-FiCERTIFIED™,Wi-FiDirect™,Wi-FiProtected Setup™,

Wi-FiMultimedia™, WPA2™, Passpoint™, and theWi-FiAlliance logo are trademarks of theWi-FiAlliance

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 maybe 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.

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

Product

Software

 

 

Description and Notes

 

 

 

 

 

 

 

 

Version

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

AT-WR4662n

1.1 b248 onward

 

 

High-SpeedMobility – Wireless base router

 

 

 

 

 

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

 

 

 

 

 

 

 

 

 

 

 

 

AT-WR4652-80

1.1 b248 onward

 

High-SpeedMobility – 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-connectAT-WR4662n

 

 

 

 

 

 

 

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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-FiMultimedia (WMM)

The Wi-FiAlliance 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-FiMultimedia?

Multimedia and data-centricapplications typically share the same network resources, despite their conflicting requirements for data delivery. Without QoS, the network offers abest-effortservice, which means that applications have equal opportunities to transfer data. WMM enables network managers to prioritize traffic based on bandwidth requirements, especiallydelay-sensitiveapplications 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-FiMultimedia works

In the IEEE 802.11 standard, the wireless nodes access the medium using the “listen-before-talk”algorithmCSMA/CA-based1 Distributed Coordination Function (DCF). The wireless node transmits a frame once its checks indicate that the medium is free for a period of distributedinter-framespace (DIFS) and a randomback-offtime 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 tohigher-prioritytraffic 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 (CWmax) is reached.Figure 1depicts the timing. In 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.

1Carrier Sense Multiple Access with Collision Avoidance.

2HCCA facility is not delivered by current software release.

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minimum wait (AIFS)

random backoff (CW)

AIFS = DIFS + 7 slots

CW = 0~15 slots

background

 

 

opportunity

 

AIFS = DIFS + 3 slots

CW = 0~15 slots

best-effort

 

 

 

AIFS = DIFS + 2 slots

CW = 0~7 slots

transmission

video

 

 

 

AIFS = DIFS + 2 slots

CW = 0~3 slots

 

 

voice

 

 

 

 

slot time

 

 

 

 

EIFS (optional)

 

 

DIFS

contention window

 

 

PIFS

 

 

busy medium

SIFS

backoff slots

 

 

 

Interframe spaces:

 

SIFS:

short interframe space

 

PIFS:

PCF interframe space

- used by HCCA facility

DIFS:

DCF interframe space

 

AISF:

arbitration interframe space

- used by QoS facility

EIFS:

extended interframe space

- used to extend the DIFS in case no ACK is received in time

Note, the node delivering data waits for DIFS before sending next frame and, within that interval, the receiver replies the ACKnowledgement frame to confirm the reception succeeded.

It may happen the receiver delays the replay, due to the signal propagation on long distance link or additional time is required by receiver for decoding and error recovery; in that case, EIFS is included giving the opportunity to return the ACK.

Figure 1 – WMM access timing

WMM requires that the clients running multimedia applications assign the appropriate priority level to the generated data traffic and that network infrastructure consistently applies QoS policies.

WMM derives four Access Categories from IEEE 802.1D Class of Service (CoS) as depicted by Table 2.

Within the wireless node, the WMM manages four independent transmit queues, one per access category, and dispatches to them incoming packets depending on the assigned Layer 3 differentiated service field (TOS/DSCP). Packet forwarding will happen basing on transmit opportunities.

Table 2 - WMM Access Categories and IEEE 802.1d tag mapping

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Access

 

 

 

 

 

 

 

 

 

IEEE 802.1D

 

 

 

 

 

Priority

 

 

Description

 

 

 

 

Category

 

 

 

 

 

 

 

Traffic Types

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Voice

 

 

Highest

 

 

Low-latencyand toll voice quality

 

 

 

6, 7

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Video

 

Highest -1

 

SDTV and HDTV streaming

 

4, 5

 

 

 

 

 

 

 

 

 

 

 

 

Best-effort

 

 

Lower + 1

 

 

Traffic less sensitive of latency, but

 

 

 

0, 3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

affected by delays

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Background

 

Lower

 

Low priority traffic without throughput

 

1, 2

 

 

 

 

 

 

 

 

 

constraint (i.e. file transfer)

 

 

 

 

 

 

 

 

 

 

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How to configure Wi-FiMultimedia

Use the command: traffic-class to set the EDCA back off criteria for the required WMM access category:

traffic-class[background|best-effort|video|voice]

cw-min<0-10>cw-max<0-10>fixed-slot<2-20>

no traffic-class[background|best-effort|video|voice]

On collisions, WMM sets the back off time within the CWmin range and uses a persistence factor (PF) as the coefficient that multiplies the contention window size in successive retransmission attempts following a collision.

 

 

 

WMM setup may only be entered on a wireless node with an access point role.

Note:

It will distribute the QoS policies to “slave” nodes, for example, non -rootbridge,

 

workgroup-bridge,etc.

 

 

Parameter descriptions

cw-min (Contention Window minimum)

That is the random wait time before retrying the transmission; the initial size of the contention window is within 0~CWmin back off slots.

The value specifies the number of back off slots as a power of 2n -1;in example,

cw-min 3 means23-1=7back off slots.cw-min 0 means20-1=0back off slots.

cw-max (Contention Window maximum)

That is the maximum size of the contention window.

The value specifies the number of back off slots as a power of 2n -1.

fixed-slot (ArbitraryInter-FrameSpace)

That is the predefined idle time that the station waits before starting the contention window (CW) .

The value specifies the number of back off slots.

Refer to “AT-WR4600– Command Reference Guide”, for default settings and

Note: recommended configuration for the different W LAN topologies (access point, bridging, etc.).

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Connecting AT-WR4600products

There are two options for accessing the Command Line Interface of the devices:

SSH remote shell, using any text-modeSSH client software.

RS-232Line Driver/Receiver that provides a standard DTE console interface; note, this is optional and is not always available.

Accessing the device via SSH

The Secure Shell (SSH) is an encrypted networking protocol, allowing the user to configure the device through an Ethernet network. Microsoft does not supply SSH tool. You can use an alternative program such as Tera Term Pro, which is licensed under GPL2. The device is factory configured with the static IP address 192.168.1.1. If the device is receiving an address from a DHCP server, please check the assigned IP address.

Accessing the device via RS-232

To access the device, you can use either the build-inMicrosoft HyperTerminal (note it was removed from Windows Vista and later versions) or an alternative program such asTera Term Pro.

The settings of the serial terminal are as follows.

Transmission rate

115200bps

 

 

Data length

8 bit

 

 

Stop bit

1bit

 

 

Parity

None

 

 

Flow control

None

 

 

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Accessing the CLI

Enter the login and password via the terminal console (SSH or RS-232).Note, by default, the login name ismanager and the password isfriend.

AT-WR4600login:manager Password:

Feb 9 10:35:07 AT-WR4600auth.info login[6898]: root login on 'ttyS0'

AA TTTTTTTTTTTTTTTTTT ooooo

AAAAA TTTTTTTTTTTTTTT oooooooo

AAAAAAAA TTTTTTTT I oooooo

AAAAAAAAAAATTTTTTT IIIIIIIIII AAAAAAA AAAAA TTTT IIIIIIIIII

AAAAAAA AAAAA T IIIIIIIIII

Copyright (C) 2012 Allied Telesis International

All rights reserved.

AT-WR4600>enable

Password:

AT-WR4600#

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Configuration example

This configuration example starts with the Command Line Interface already set to Global configuration mode:

AT-WR4600#configureterminal

AT-WR4600(config)#

On setup completion, run the command show running-config to verify the applied configuration.

All of the examples in this document provide the minimum set of commands Note: useful for configuring the WMM, regardless of other services like bridging, and

security etc.

Using QoS to prioritize voice traffic

This example applies the QoS policy to support voice traffic.

Wireless nodes belong to a Wireless Distribution System working in 5GHz bands, while the access to a wireless LAN is offered in 2GHz bands.

10.0.0.0/24

AP

Bridge0

10.0.0.0/24

STA AP

Bridge1

AP1

10.0.0.0/24

STA

Bridge2

Figure 2 – QoS giving preference to voice traffic

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