Tutorial on draft D3.0 of IEEE P802.11

V. Hayes

Description

03/08/96doc.: IEEE P802.11-96/49BMarch 1996802.11 Tutorial March 96802.11 ArchitectureCopyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change 1802.11 Tutorial March 96What is unique about wireless?• Difficult media– interference and noise– quality varies over space and time– shared with “unwanted” 802.11 devices– shared with non-802 devices (unlicensedspectrum, microwave ovens)• Full connectivity cannot be assumed– “hidden node” problem• Multiple international regulatory requirementsCopyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change 2Submission 1 Greg Ennis, Symbol Technologies* 1103/08/96doc.: IEEE P802.11-96/49BMarch 1996802.11 Tutorial March 96Medium VariationsCopyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change 3802.11 Tutorial March 96Uniqueness of Wireless (continued)• Mobility– variation in link reliability– battery usage: requires power management– want “seamless” connections• Security– no physical boundaries– overlapping LANsCopyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change 4Submission 2 Greg Ennis, Symbol Technologies* 2203/08/96doc.: IEEE P802.11-96/49BMarch 1996802.11 Tutorial March 96Requirements• Single MAC to support multiple PHYs.– Support single and multiple channel PHYs.– PHYs with different ...

Informations

• Publié par: Octe
• Nombre de lectures: 12
• Langue: English

Extrait

1

March 1996

03/08/96

*

1

doc.: IEEE P802.11-96/49B

Submission

1

Greg Ennis, Symbol Technologies

802.11 Tutorial

1

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

802.11 Architecture

802.11 Tutorial

2

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

What is unique about wireless?

• Difficult media

–interference and noise

–quality varies over space and time

–shared with “unwanted” 802.11 devices

–shared with non-802 devices (unlicensed

spectrum, microwave ovens)

• Full connectivity cannot be assumed

–“hidden node” problem

• Multiple international regulatory requirements

2

March 1996

03/08/96

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2

doc.: IEEE P802.11-96/49B

Submission

2

Greg Ennis, Symbol Technologies

802.11 Tutorial

3

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

Medium Variations

802.11 Tutorial

4

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

Uniqueness of Wireless (continued)

• Mobility

– variation in link reliability

– battery usage: requires power management

– want “seamless” connections

• Security

– no physical boundaries

– overlapping LANs

3

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Submission

3

Greg Ennis, Symbol Technologies

802.11 Tutorial

5

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

Requirements

• Single MAC to support multiple PHYs.

– Support single and multiple channel PHYs.

– PHYs with different “Medium Sense” characteristics.

• Should allow overlap of multiple networks in the

same area and channel space.

• Need to be “Robust for Interference”.

– Microwave, other non-802.11 interferers.

– Co-channel interference.

• Need mechanisms to deal with “Hidden Nodes”.

• Need provisions for Time Bounded Services.

802.11 Tutorial

6

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

Architecture Overview

• One MAC supporting multiple PHYs

– currently Frequency Hopping, Direct Sequence and

Infrared PHYs

• Two configurations

– “Independent” (ad hoc) and “Infrastructure”

• CSMA/CA (collision avoidance) with optional

“point coordination”

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Submission

4

Greg Ennis, Symbol Technologies

802.11 Tutorial

7

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

802.11 Protocol Entities

MAC

Sublayer

PLCP Sublayer

PMD Sublayer

MAC Layer

Management

PHY Layer

Management

Station

Management

LLC

MAC

PHY

802.11 Tutorial

8

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

802.11 Protocol Architecture

• MAC Entity

– basic access mechanism

– fragmentation

– encryption

• MAC Layer Management Entity

– synchronization

– power management

– roaming

– MAC MIB

• Physical Layer Convergence Protocol (PLCP)

– PHY-specific, supports common PHY SAP

– provides Clear Channel Assessment signal (carrier

sense)

5

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Submission

5

Greg Ennis, Symbol Technologies

802.11 Tutorial

9

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

802.11 Protocol Architecture

(cont.)

• Physical Medium Dependent Sublayer (PMD)

– modulation and encoding

• PHY Layer Management

– channel tuning

– PHY MIB

• Station Management

– interacts with both MAC Management and PHY

Management

802.11 Tutorial

10

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

802.11 Configurations - Independent

• Independent

– one “Basic Service Set”, BSS

– “Ad Hoc” network

– direct communication

– limited coverage area

Station

AH3

Station

Station

AH1

AH2

Ad Hoc Network

6

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Submission

6

Greg Ennis, Symbol Technologies

802.11 Tutorial

11

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

802.11 Configurations - Infrastructure

• Infrastructure

–Access Points and stations

• Distribution System

interconnects Multiple Cells

via Access Points

to form a single Network.

–extends wireless coverage area

Station

Station

Station

Station

A1

A2

B1

B2

BSS-A

BSS-B

A

AP

AP

B

Server

DISTRIBUTION SYSTEM

802.11 Tutorial

12

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

Distribution System

• Used to interconnect wireless cells

– multiple BSS connected together form an ESS, Extended

Service Set

– Allows mobile stations to access fixed resources

• Not part of 802.11 standard

– could be bridged IEEE LANs, wireless, other networks …

– Distribution System Services are defined

7

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Submission

7

Greg Ennis, Symbol Technologies

802.11 Tutorial

13

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

Access Points

• Stations select an AP and “associate” with it

• Support roaming

• Provide other functions

– time synchronization (beaconing)

– power management support

– point coordination function

• Traffic typically (but not always) flows through AP

– direct communication possible

802.11 Tutorial

14

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

802.11 Defines the Airwaves IF

• The airwaves interface between stations

(including that between station and AP) is

standardized

– PHY and MAC

• No exposed MAC/PHY interface specified

• No exposed interface to Distribution System

– required DS services are defined

• Internals of Distribution System not defined

8

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Submission

8

Greg Ennis, Symbol Technologies

802.11 Tutorial

15

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

MAC Services

• Asynchronous MSDU Data Delivery

– provided to LLC (2304 octet maximum)

• Time Bounded Services

– optional point coordination function

• Security Services

– confidentiality, authentication, access control

• Management Services

– scanning, joining, power management

802.11 Tutorial

16

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

MAC Functionality

• Independent and Infrastructure configuration

support

– Each BSS has a unique 48 bit address

– Each ESS has a variable length address

• CSMA with collision avoidance

– MAC-level acknowledgment

– allows for RTS/CTS exchanges

» hidden node protection

– MSDU fragmentation

– “Point Coordination” option

» AP polling

9

March 1996

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doc.: IEEE P802.11-96/49B

Submission

9

Greg Ennis, Symbol Technologies

802.11 Tutorial

17

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

MAC Functionality (continued)

• Roaming support within an ESS

– station scans for APs, association handshakes

• Power management support

– stations may power themselves down

– AP buffering, distributed approach for IBSS

• Authentication and privacy

– Optional support of “Wired Equivalent Privacy” (WEP)

– Authentication handshakes defined

802.11 Tutorial

18

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

PHY Layer Services

• PHY_DATA transfers

– multiple rates

• Clear Channel Assessment (CCA)

– carrier sense

• PHY Management

– channel tuning

10

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Submission

10

Greg Ennis, Symbol Technologies

802.11 Tutorial

19

March

96

Copyright ©1996 IEEE, All rights reserved. This contains parts from an unapproved draft, subject to change

Three PHYs

• Frequency Hop Spread Spectrum

– 2.4 GHz band, 1 and 2 Mbps transmission

– 2GFSK, 4GFSK

– hop over 79 channels (North America)

• Direct Sequence Spread Spectrum

– 2.4 GHz band, 1 and 2 Mbps transmission

– DBPSK, DQPSK

– 11 chip Barker sequence

• Baseband IR

– Diffuse infrared

– 1 and 2 Mbps transmission, 16-PPM and 4-PPM