The 802 11 mac protocol quality of service
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The 802.11 MAC Protocol & Quality of Service. Duncan Kitchin Wireless Networking Group Intel Corporation 4/4/2003. Agenda. 802.11 MAC Overview QoS Objectives & Applications Important Questions 802.11e Details Future Developments & Summary. 802.11 MAC Overview.

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The 802 11 mac protocol quality of service

The 802.11 MAC Protocol &Quality of Service

Duncan Kitchin

Wireless Networking Group

Intel Corporation

4/4/2003


Agenda

Agenda

  • 802.11 MAC Overview

  • QoS Objectives & Applications

  • Important Questions

  • 802.11e Details

  • Future Developments & Summary


802 11 mac overview

802.11 MAC Overview


802 11 logical architecture

802.11 Logical Architecture

Application

Presentation

LLC (802.2)

Session

MAC

Transport

Network

PHY

Data link

Physical


802 11 sublayers

802.11 sublayers

802.11c

802.11F

Higher layers

MAC

802.11d

802.11e

802.11h

802.11i

PHY

802.11a

802.11b

802.11g

Extensions are “mix and match”


Standards decoder ring

Standards decoder ring

  • 802.11a5GHz OFDM PHY

  • 802.11b2.4GHz CCK PHY

  • 802.11c802.11 bridging

  • 802.11dInternational roaming

  • 802.11eQoS/efficiency enhancements

  • 802.11FInter AP protocol

  • 802.11g2.4GHz OFDM PHY

  • 802.11h5GHz regulatory extensions

  • 802.11iSecurity enhancements

  • 802.11jJapan 5GHz band extensions

  • 802.11kRadio resource measurement

  • 802.11lSkipped (typographically unsound)

  • 802.11mMaintenance

  • 802.11nHigh throughput PHY


Origins of the 802 11 mac

Origins of the 802.11 MAC

  • Derived from Ethernet (CSMA/CD) philosophy

  • Developed into present form 1990-1994

  • Required much modification to fit wireless medium

    • CSMA/CA

  • Widely regarded at the time as a kludge


New 802 11 mac developments

New 802.11 MAC developments

  • 802.11e is the “new” MAC

    • evolution to base 802.11

    • adds differentiated QoS…

    • …but also enhanced efficiency

  • Core components represent a simple evolution

  • Optional extensions may be widely implemented in the future, subject to market demand


Qos objectives applications

QoS Objectives & Applications


What does qos mean

What Does QoS Mean?

  • We limit the definition to mean “delivering traffic for real-time applications”

  • Each application has a requirements tuple

    • max latency

    • min data rate

    • max packet drop probability

  • The set of tuples define points that delimit the requirements curve


Representation of requirements

Representation of Requirements

  • Define a set of applications first

    • voice

    • gaming

    • real-time video (videoconferencing)

    • “CD like” audio

    • “Television/VCR like” video

  • Each of these applications defines a point on the data rate/latency/drop rate requirements curve


Why 802 11e and 802 11a

Why 802.11e and 802.11a

  • Home wireless network usage model shift

  • 802.11b in home networks was driven by broadband Internet connection sharing

  • 802.11a in home networks will be driven by high bandwidth multimedia streams between devices in the home


New usage models

TV

Tablet

New Usage Models

BB

Gateway

PC

PC


Applications

Applications

  • Video

  • Audio

  • Voice

  • Gaming

  • Videoconferencing


Video

Video

  • Key motivation for multimedia home networks

  • High quality, streaming video

  • Focus on MPEG-2, MPEG-4, wmv

  • Lowest mean rate 2Mb/s (SD)

  • Highest mean rate 20Mb/s (HD)

  • Variable data rate requirements


Audio

Audio

  • High quality, streaming audio has distinct requirements from voice

  • Key formats MP3, wma, PCM

  • Bandwidth range 64kb/s up to 1.5Mb/s

  • Relatively high latency tolerance


Voice videoconferencing

Voice & videoconferencing

  • Low latency

    • < 50ms required

  • Lower bandwidth requirements

    • 32kb/s and lower for voice

    • 128kb/s for videoconferencing

  • Higher tolerance to frame losses


Gaming

Gaming

  • Lowest latency

    • < 10ms required

  • Lower bandwidth requirements

    • 32kb/s – 128kb/s?

  • Low tolerance to frame loss


Applications summary

Applications Summary

Video

Audio

Latency tolerance

Videoconference

Voice

Gaming

Bandwidth


Important questions

Important Questions


The protocol stack

The Protocol Stack

Application

Transport

TCP/UDP

Network

IP

DLC (MAC + LLC)

PHY


The protocol stack1

The Protocol Stack

  • Before defining the link layer (MAC) must decide what the higher layers are

  • If we assume TCP/IP based higher layers, that imposes restrictions on what we can do

  • We don’t have latitude to rewrite TCP/IP, or the interface to it

  • We also don’t have latitude to rewrite the applications or the OS


What we must do

What We Must Do

  • Define 802.11 MAC as providing a set of services

  • Those services are defined by the 802.2 service primitives, incorporating 802.1D

  • Deliver packets, each of which is tagged with a 3-bit priority

  • Consider each service request packet-by-packet

    • we have no mechanism to tell us about connections from the higher layers


What the services will look like in qos terms

What the Services Will Look Like in QoS Terms

  • Each packet, dependent on priority, will have a latency probability distribution

  • If the higher layers (or the MAC) imposes a timeout, there will be a drop probability against timeout curve

  • Need to revisit requirements to see what the bounds for the curve should be


802 11e details

802.11e Details


802 11e features

Direct link

Group acknowledge

EDCF/WME

Core functionality

Point coordinated mode

802.11e features


802 11e features1

802.11e Features

  • CSMA

  • Direct link

  • Block acknowledge

  • Point coordinated mode


Csma strategy

CSMA Strategy

  • Use 802.1D tags to classify traffic into groups with widely differing requirements

  • 8 priority levels grouped into four classes

    • best effort

    • video/audio probe

    • video/audio

    • voice/gaming


Applying to different classes

Applying to different classes

  • Priority access improves chances of getting access to the medium quickly

  • Long burst duration provides high bandwidth access, but at the expense of latency

  • Set appropriately:

    • voice/gaming has very high access priority, small burst size

    • video/audio has much lower access latency (but better than best effort) but large burst sizes


802 11e direct link

802.11e Direct Link

  • 802.11-1997 specification permits traffic in an AP-based network between clients and AP only

  • 802.11e adds capability for clients to send traffic directly to each other

    • improves bandwidth efficiency, particularly in home networks


Direct link

Direct Link

AP

Station

Station


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