itg wlan theory - security

16.09.03 / WLAN_Theory.ppt / Seite 1

WLAN Grundlagen

ITG Informationstagung "Wireless LAN"

Prof. Dr. Andreas SteffenZürcher Hochschule WinterthurProf. Dr. Jean-Frédéric Wagen

Ecole d‘ingénieurs et d‘architectes de Fribourg


Contents

• WLAN IEEE 802.11 Architecture

• WLAN Frequency Bands

• WLAN Data Rates & Throughput

• WLAN Coverage & Range

• WLAN Standards & Compatibility

• References


IEEE 802.11 WLAN ArchitectureWired LAN

Access Point(AP)

Wireless Station(STA)

• Basic Service Set (BSS) operating in infrastructure mode controlled by access point

Wireless Station(STA)

STA

STA

• Independent Basic Service Set (IBSS) operating in ad hoc modeforms a peer-to-peer network


IEEE 802.11 Extended Service Set (ESS)

Bridging based on theInter-Access-Point Protocol

(IAPP)"Roaming"


Synchronisation and Power Management

Wired LANSTA AP

- sends periodic beaconfor synchronization

- AP will cache messagesfor dozing STA

- is either awake or dozing- must inform AP- must wake-up periodically.


replies with CTScontaining TX duration

IEEE 802.11 CSMA-CA and TX Reservation

Hidden Terminal Problem

sends RTScontaining TX duration

sets NAV via RTS

sets NAV via CTS

CSMACarrier SenseMultiple Access

CACollision Avoidance

TXTransmit

RTSRequest to Send

CTSClear to Send

NAVNetwork Allocation Vector



WLAN

Frequency Bands


ISM Unlicensed Frequency Bands

Audio

AM BroadcastShort-Wave Radio FM Broadcast

Television Infrared Wireless LAN

Cellular (840MHz)NPCS (1.9GHz)

ExtremelyLow

VeryLow

Low Medium High VeryHigh

UltraHigh

SuperHigh

Infrared VisibleLight

Ultra-violet

X-Rays

902–928 MHz26 MHz

Remote Control,etc.

902902––928 MHz928 MHz26 MHz26 MHz

Remote Control,Remote Control,etc.etc.

5.2 GHz100 MHz

(IEEE 802.11a)HIPERLAN 1+2

5.2 GHz5.2 GHz100 MHz100 MHz

(IEEE 802.11a)(IEEE 802.11a)HIPERLAN 1+2HIPERLAN 1+2

2.4–2.4835 GHz83.5 MHz

(IEEE 802.11b)Microwave Ovens

2.42.4––2.4835 GHz2.4835 GHz83.5 MHz83.5 MHz

(IEEE 802.11b)(IEEE 802.11b)Microwave OvensMicrowave Ovens

Industrial, Scientific and Medical Band

© 2001, Cisco Systems, Inc.


IEEE 802.11 DSSS Frequency Channel Plan


IEEE 802.11 DSSS Frequency Channel Plan

1 2 3 4 5 6 7 8 9 10 11

1

2

3

4

5

6

7

8

9

10

11

Channel

Frequency2400 248324372412 MHz

22 MHz

5 MHz

12 13

2462 2472

12

13

• 13 channels in Europe (ETSI) from 2412 MHz to 2472 MHz, spaced by 5 MHz. Only first 11 channels available in USA.

• 22 MHz carrier bandwidth.• Only 3-4 non-overlapping channels (USA: 1,6,11 / ETSI: 1,5,9,13).

BAKOM recommends channels 1,7,13 for use in Switzerland



WLANData Rates & Throughput


IEEE 802.11 DSSS Radio Interface

• 1 Mbps 1 Msymbol/s BPSK spread by 11 chip Barker code,(-4 dB Bandwidth = 11 MHz, main lobe = 22 MHz), IEEE 802.11

• 2 Mbps 1 Msymbol/s QPSK spread by 11 chip Barker code(-4 dB Bandwidth = 11 MHz, main lobe = 22 MHz), IEEE 802.11

• 5.5 Mbps 2 Msymbol/s QPSK like symbols spread by 8 chip Complementary Code Keying (CCK). IEEE 802.11b

• 11 Mbps 4 Msymbol/s QPSK like symbols spread by 8 chip Complementary Code Keying (CCK). IEEE 802.11b

• 54 Mbps OFDM with max. 52 sub-carriers, IEEE 802.11a / IEEE 802.11g

raw bit rate is not equalto net bit rate or throughput !

raw bit rate is not equalto net bit rate or throughput !

• 50% max. of the raw bit rate (good reception quality, no interference)



WLANCoverage & Range


office

2 Mbps

IEEE 802.11b Maximum Distance Range

100 m

semi-open2 Mbps

semi-open11 Mbps

open11 Mbps 2 Mbps

open

office11 Mbps


ETSI regulations at 2.4 GHz:EIRP = G ⋅ P < 100 mW

Antenna Input Power P = 100 mW / G Reception Gain G

Point-to-point WLAN connectionsusing directional antennas

Effective Isotropic Radiated Power (EIRP)

Typical single antenna gainG = 10 .. 24 dBi

Covered distanced ≈ 1 .. 3 km



WLAN

Standards & Compatibility


Scope of IEEE 802.11 Standard

3

4

5

6

7

OSI layers• Original IEEE 802.11 standard specifies layer 1

and lower part of layer 2 only• For multi-vendor WLAN roaming, bridging and

routing standards are needed


IEEE 802.11 Task Group Outline

• 802.11 Specification of WLAN MAC and PHY layers(IR, FH and DSSS at 2.4 GHz), ratified in 1997/1999

• 802.11a PHY layer at 5 GHz (54 Mbps DSSS), ratified in 1999

• 802.11b 11 Mbps DSSS at 2.4 GHz, ratified in 1999

• 802.11c Improvements of the MAC layer (Internal Sub-Layer Service)

• 802.11d Update (frequency spectrum regulations)

• 802.11e Improvements of the MAC layer (Quality of Service)

• 802.11f Inter-Access Point Protocol (IAPP)

• 802.11g Higher Data rate (>20 Mbps) at 2.4 GHz

• 802.11h Dynamic Channel Selection and Transmit Power Control mechanisms

• 802.11i Authentication and Security

http://grouper.ieee.org/groups/802/11/QuickGuide_IEEE_802_WG_and_Activities.htm


802.11b Interoperability


References[1] IEEE 802.11 (= ISO/IEC 8802-11: 1999), Part 11: Wireless LAN Medium Access

Control (MAC) and Physical Layer (PHY) Specifications, ANSI/IEEE Std 802.11,1999 Edition, http://ieee802.org/11.

[2] IEEE Std 802.11b-1999 (Supplement to ANSI/IEEE Std 802.11, 1999 Edition),Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Higher-Speed Physical Layer Extension in the 2.4 GHz Band,ISBN 0-7381-1812-5, http://ieee802.org/11.

[3] BAKOM – Bundesamt für Kommunikation,www.bakom.ch/imperia/md/content/deutsch/telecomdienste/factsheets/factsheet_wlan.pdf

[4] Jean-Frédéric Wagen ([email protected]), EIF, and Andreas Steffen, ZHW,Swisscom Seminar – Access Technologies, Fribourg, October 2002.

[5] Vincent Bieri ([email protected]), Wireless LAN (WLAN) – An Introduction,Séminaire Technique, EIA-FR, March 2002

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