TECHNISCHE UNIVERSITÄT ILMENAU IEEE 802...Basic Service Set (BSS): group of stations using the same...

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IEEE 802.11

CharacteristicsSystem ArchitectureProtocol ArchitecturePhysical LayerMAC Layer MAC Management

Power ManagementRoamingCurrent Developments

Wireless Internet 2Andreas Mitschele-Thiel 9-Sep-07

Characteristics of Wireless LANs

Advantagesvery flexible alternative to wired LANs(almost) no wiring difficulties (e.g. historic buildings, firewalls)ad-hoc networks without previous planning possiblemore robust against disasters, e.g. earthquakes, fire, or users pulling a plug ...

Disadvantageslower bandwidth compared to wired networks possible interference may reduce bandwidthno guaranteed service due to license-free spectrumneed to consider security issuesproprietary solutions, especially for higher bit-rateswireless products have to follow many national restrictions=> long time to establish global standards like, e.g. IMT-2000 (UMTS)


Design goals for Wireless LANs

global, seamless operation

low power for battery use

no special permissions or licenses needed to use the LAN

robust transmission technology

simplified spontaneous cooperation at meetings

easy to use for everyone, simple management

protection of investment in wired networks

security (no one should be able to read my data), privacy (no one should be able to collect user profiles), safety (low radiation)

transparency concerning applications and higher layer protocols,but also location awareness if necessary


Comparison: Infrared vs. Radio Transmission

Infrareduses IR diodes, diffuse light, multiple reflections (walls, furniture etc.)

Advantagessimple, cheap, available in many mobile devicesno licenses neededsimple shielding possible

Disadvantagesinterference by sunlight, heat sources etc.many things shield or absorb IR light low bandwidth

ExampleIrDA (Infrared Data Association) interface available everywhere

Radiotypically using the license free ISM band at 2.4 GHz

Advantagesexperience from wireless WAN and mobile phones can be used coverage of larger areas possible (radio can penetrate walls, furniture etc.)

Disadvantagesvery limited license-free frequency bands shielding more difficult, interference with other electrical devices

Examples802.11a/b/g, HIPERLAN1/2, Bluetooth, ZigBee


Comparison: Infrastructure vs. Ad-hoc Networks

infrastructurenetwork

ad-hoc network

APAP

AP

wired network

AP: Access Point


Distribution System

Portal

802.x LAN

AccessPoint

802.11 LAN

BSS2

802.11 LAN

BSS1

AccessPoint

Station (STA)terminal with access mechanisms to the wireless medium and radio contact to the access point

Basic Service Set (BSS)group of stations using the same radio frequency

Access Pointstation integrated into the wireless LAN and the distribution system

Portalbridge to other (wired) networks

Distribution Systeminterconnection network to form one logical network (ESS: Extended Service Set) based on several BSS

802.11: Architecture of an Infrastructure Network

STA1

STA2 STA3

ESS


802.11: Architecture of an Ad-hoc Network

Direct communication within a limited range

Station (STA):terminal with access mechanisms to the wireless mediumBasic Service Set (BSS):group of stations using the same radio frequency

802.11 LAN

BSS2

802.11 LAN

BSS1

STA1

STA4

STA5

STA2

STA3


IEEE Standard 802.11

mobile terminal

access point

server

fixed terminal

application

TCP

802.11 PHY

802.11 MAC

IP

802.3 MAC

802.3 PHY

application

TCP

802.3 PHY

802.3 MAC

IP

802.11 MAC

802.11 PHY

LLC

infrastructure network

LLC LLC


802.11 – Layers and Functions

PLCP (Physical Layer Convergence Protocol)clear channel assessment signal (carrier sense)

PMD (Physical Medium Dependent)modulation, coding

PHY Managementchannel selection, MIB

Station Managementcoordination of all management functions

PMD

PLCP

MAC

LLC

MAC Management

PHY Management

MACaccess mechanisms, fragmentation, encryption

MAC Managementsynchronization, roaming, MIB, power management

PHY

DLC

Sta

tion

Man

agem

ent


802.11 – Physical Layer

3 versions: 2 radio (typ. 2.4 GHz), 1 IRdata rates 1 or 2 Mbit/s

FHSS (Frequency Hopping Spread Spectrum)spreading, despreading, signal strength, typ. 1 Mbit/smin. 2.5 frequency hops/s (USA), two-level GFSK modulation

DSSS (Direct Sequence Spread Spectrum)DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift Keying), DQPSK for 2 Mbit/s (Differential Quadrature PSK)preamble and header of a frame is always transmitted with 1 Mbit/s, rest of transmission 1 or 2 Mbit/schipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1 (Barker code)max. radiated power 1 W (USA), 100 mW (EU), min. 1mW

Infrared850-950 nm, diffuse light, typ. 10 m rangecarrier detection, energy detection, synchonization


FHSS PHY Packet Format

synchronization SFD PLW PSF HEC payload

PLCP preamble PLCP header

80 16 12 4 16 variable bits

802.11 only, not 802.11a/b!Synchronization

synch with 010101... patternSFD (Start Frame Delimiter)

0000110010111101 start patternPLW (PLCP_SDU Length Word)

length of payload incl. 32 bit CRC of payload, PLW < 4096 (octets)PSF (PLCP Signaling Field)

data rate of packet (1 or 2 Mbit/s)HEC (Header Error Check)

CRC with x16+x12+x5+1


DSSS PHY Packet Format

synchronization SFD signal service HEC payload



length16

802.11 (802.11b)Synchronization

synch., gain setting, energy detection, frequency offset compensation

SFD (Start Frame Delimiter)1111001110100000

Signaldata rate of the packet (0A: 1 Mbit/s DBPSK; 14: 2 Mbit/s DQPSK)

Service Lengthfuture use, 00: 802.11 compliant length of the payload

HEC (Header Error Check)protection of signal, service and length, x16+x12+x5+1


802.11 MAC Layer – DFWMAC

Traffic servicesAsynchronous Data Service (mandatory)

exchange of data packets based on "best-effort"support of broadcast and multicastimplemented using DCF (Distributed Coordination Function)

Time-Bounded Service (optional)implemented using PCF (Point Coordination Function)

Access methodsDFWMAC-DCF CSMA/CA (mandatory)

Distributed Foundation Wireless MACcollision avoidance via randomized "back-off" mechanismminimum distance between consecutive packetsACK packet for acknowledgements (not for broadcasts)

DFWMAC-DCF with RTS/CTS Extension (optional)avoids hidden terminal problem

DFWMAC- PCF (optional)access point polls terminals according to a list


802.11 MAC

Prioritiesdefined through different Inter-Frame Spaces (IFSs)no guaranteed, hard prioritiesSIFS (Short Inter-Frame Spacing)

highest priority, for ACK, CTS, polling responsePIFS (PCF IFS)

medium priority, for time-bounded service using PCFDIFS (DCF IFS)

lowest priority, for asynchronous data service

t

medium busy

DIFSDIFS

next framecontention

direct access ifmedium is free ≥ DIFS

SIFSPIFS


802.11 – Timing DetailsTransmission and Processing Delays

Times for 802.11aSlotTime – 9 μsSIFS – 16 μsPIFS – 25 μsDIFS – 34 μs


t

medium busy

DIFSDIFS

next frame

contention window(randomized back-offmechanism)

802.11 – CSMA/CA Access Method

station ready to send starts sensing the medium (Carrier Sense based on CCA, Clear Channel Assessment)if the medium is free for the duration of an Inter-Frame Space (IFS), the station can start sending (IFS depends on service type)if the medium is busy, the station has to wait for a free IFS, then the station must additionally wait a random back-off time (collision avoidance, multiple of slot-time) if another station occupies the medium during the back-off time of the station, the back-off timer stops (fairness)

slot timedirect access ifmedium is free ≥ DIFS

SIFSPIFS


802.11 – Competing Stations – Simple Version

t

busy

boe

station1

station2

station3

station4

station5

packet arrival at MAC

DIFSboe

boe

boe

busy

elapsed backoff time

bor residual backoff time

busy medium not idle (frame, ack etc.)

bor

bor

DIFS

boe

boe

boe bor

DIFS

busy

busy

DIFSboe busy

boe

boe

bor

bor


802.11 – CSMA/CA Access Method

Sending unicast packetsstation has to wait for DIFS before sending datareceivers acknowledge at once (after waiting for SIFS) if the packet was received correctly (CRC)automatic retransmission of data packets in case of transmission errors

t

SIFS

DIFS

data

ACK

waiting time

otherstations

receiver

sender data

DIFS

contention


Hidden Terminal Problem

A sends to B, C cannot receive A C wants to send to B, C senses a “free” medium -> CS failscollision at B, A cannot receive the collision -> CD failsA is “hidden” for C

=> Application of RTS/CTS

A B C


802.11 – DCF with RTS/CTS Extension

Sending unicast packetsstation can send RTS with reservation parameter after waiting for DIFS (reservation determines amount of time the data packet needs the medium) acknowledgement via CTS after SIFS by receiver (if ready to receive)sender can now send data at once, acknowledgement via ACKother stations store medium reservations distributed via RTS and CTS

t

SIFS

DIFS

data

ACK

defer access

otherstations

receiver

sender data

DIFS

contention

RTS

CTSSIFS SIFS

NAV (RTS)NAV (CTS)

NAV: network allocation vector (implicit in RTS and CTS)


Fragmentation

t

SIFS

DIFS

data

ACK1

otherstations

receiver

sender frag1

DIFS

contention

RTS

CTSSIFS SIFS

NAV (RTS)NAV (CTS)

NAV (frag1)NAV (ACK1)

SIFSACK2

frag2

SIFS


802.11 – PCF (Polling)

PIFS

stations‘NAV

wirelessstations

point coordinator

D1

U1

SIFS

NAV

SIFSD2

U2

SIFS

SIFS

SuperFramet0

medium busy

t1

SuperFrame defines time span for polling of (all) wireless stations by AP (including time to reply)

D1: polling of wireless station 1U1: station 1 responds to polling by sending its dataD2: polling of wireless station 2U2: station 2 responds to polling by sending its data


802.11 – PCF (Polling)

tstations‘NAV

wirelessstations

point coordinator

D3

NAV

PIFSD4

U4

SIFS

SIFSCFend

contentionperiod

contention free period

t2 t3 t4

D3: polling of wireless station 3U3: no data -> no response by station 3 within SIFSD4 (after PIFS): polling of wireless station 4U4: station 4 responds to polling by sending its data

Discussion:unpredictable beacon delaysunknown transmission duration of polled stations

=> no QoS guarantees


802.11 – MAC Frame Format

Types (frame control)control frames, management frames, data frames

Sequence numberimportant against duplicated frames due to lost ACKs

Addressesreceiver, transmitter (physical), BSS identifier, sender (logical)

Miscellaneousduration (NAV), checksum, data

FrameControl

Duration/ID

Address1

Address2

Address3

SequenceControl

Address4 Data CRC

2 2 6 6 6 62 40-2312bytes

Protocolversion Type Subtype To

DSMoreFrag Retry Power

MgmtMoreData WEP

4 12 2FromDS

1

Order

bits 1 1 1 1 1 1


MAC Address Format

scenario to DS from DS

address 1 address 2 address 3 address 4

ad-hoc network 0 0 DA SA BSSID - infrastructure network, from AP

0 1 DA BSSID SA -

infrastructure network, to AP

1 0 BSSID SA DA -

infrastructure network, within DS

1 1 RA TA DA SA

DS: Distribution System AP: Access PointDA: Destination Address SA: Source AddressBSSID: Basic Service Set Identifier RA: Receiver AddressTA: Transmitter Address

FrameControl Duration DA SA BSSID Sequence

Control Frame Body CRC

2 2 6 6 6 2 40-2312bytes

Management frame format


Control Frames: ACK, RTS, CTS

Acknowledgement

Request To Send

Clear To Send

FrameControl Duration Receiver

AddressTransmitter

Address CRC

2 2 6 6 4bytes


Address CRC

2 2 6 4bytes


Address CRC

2 2 6 4bytes

ACK

RTS

CTS

Duration is used to determine NAV value


802.11 – MAC Management

Synchronizationtry to find a LAN, try to stay within a LANsynchronization of internal clocks to coordinate access (e.g. SIFS, PIFS, etc.), send beacons, etc.

Power managementsleep-mode without missing a messageperiodic sleep, frame buffering, traffic measurements

Association/Reassociationintegration into a LANroaming, i.e. change networks by changing access points scanning, i.e. active search for a network

MIB - Management Information Basemanaging, read, write


Synchronization Using a Beacon (Infrastructure)

beacon interval

tmedium

accesspoint

busy

B

busy busy busy

B B B

value of the timestamp B beacon frame

Beacon sent only by access pointBeacon may be delayed due to busy medium; beacon interval is not influenced by this!


Synchronization Using a Beacon (Ad-hoc)

tmedium

station1

busy

B1

beacon interval

busy busy busy

B1

value of the timestamp B beacon frame

station2B2 B2

random delay

Beacon may be sent by any station (sending of beacon employs a random delay to avoid collisions)


Power Management

Idea: switch the transceiver off if not needed

States of a station: sleep and awake

Timing Synchronization Function (TSF)stations wake up at the same time

InfrastructureAP stores frames intended for sleeping stationsAP transmits indication about stored frames in periodic beacons (Indication Maps) sent during awake interval

Traffic Indication Map (TIM): List of unicast receiversDelivery Traffic Indication Map (DTIM): List of broadcast/multicast receivers

Ad-hocAd-hoc Traffic Indication Map (ATIM)

announcement of receivers by stations buffering framesmore complicated - no central APcollision of ATIMs possible (scalability?)


Power Saving with Wake-up Patterns (Infrastructure)

TIM interval

t

medium

accesspoint

busy

D

busy busy busy

T T D

T TIM D DTIM

DTIM interval

BB

B broadcast/multicast

station

awake

p PS poll

p

d

d

d data transmissionto/from the station

beacon indicates station that data are available

station replies with PS (power save) poll and continues listening to the medium

AP transmits datastation acknowledges the data


Power Saving with Wake-up Patterns (Ad-hoc)

awake

A transmit ATIM D transmit data

t

station1B1 B1

B beacon frame

station2B2 B2

random delay

A

a

D

d

ATIMwindow beacon interval

a acknowledge ATIM d acknowledge data

medium busy busy busy


802.11 – Roaming

No or bad connection? Then perform:

Scanningscan the environment, i.e.

listen into the medium for beacon signals or send probes into the medium and wait for an answer

=> time-consuming (scan all channels)

Association Requeststation sends a request to an AP

Association Responsesuccess: AP has answered, station can now participatefailure: continue scanning

AP accepts Reassociation Requestsignal the new station to the distribution systemthe distribution system updates its data base (i.e. location information)the distribution system may inform the old AP so it can release resources802.11f standard (IAPP – Inter AccessPoint Protocol)


WLAN: IEEE 802.11b

Data rate1, 2, 5.5, 11 Mbit/s, depending on SNR User data rate max. approx. 6 Mbit/s

Transmission range300m outdoor, 30m indoorMax. data rate ~10m indoor

FrequencyFree 2.4 GHz ISM-band

SecurityLimited, WEP insecure, SSID

Cost25€ adapter, 100€ base station

AvailabilityMany products, many vendors

Connection set-up timeConnectionless/always on

Quality of ServiceTyp. best effort, no guarantees (unless polling is used, limited support in products)

ManageabilityLimited (no automated key distribution, sym. encryption)

Advantages/DisadvantagesAdvantage: many installed systems, lot of experience, available worldwide, free ISM band, many vendors, integrated in laptops, simple systemDisadvantage: heavy interference on ISM band, no service guarantees, slow relative speed only


IEEE 802.11b – PHY Frame Formats

synchronization SFD signal service HEC payload



length16

192 µs at 1 Mbit/s DBPSK 1, 2, 5.5 or 11 Mbit/s

short synch. SFD signal service HEC payload

PLCP preamble(1 Mbit/s, DBPSK)

PLCP header(2 Mbit/s, DQPSK)


length16

96 µs 2, 5.5 or 11 Mbit/s

Long PLCP PPDU format 8 (corresponds to 802.11)

Short PLCP PPDU format (optional)


Channel Selection (Non-overlapping)

2400[MHz]

2412 2483.52442 2472

channel 1 channel 7 channel 13

Europe (ETSI)

US (FCC)/Canada (IC)

2400[MHz]

2412 2483.52437 2462

channel 1 channel 6 channel 11

22 MHz

22 MHz


WLAN: IEEE 802.11g

Data rate6, 9, 12, 18, 24, 36, 48, 54 Mbit/s, depending on SNRUser throughput (1500 byte packets): 5.3 (6), 18 (24), 24 (36), 32 (54) 6, 12, 24 Mbit/s mandatory

Transmission range150m outdoor, 20m indoor54 Mbit/s up to 6 m

Frequency2.412~2.472GHz (Europe ETSI)2.457~2.462GHz (Spain)2.457~2.472GHz (France)



AvailabilitySome products, some vendors


Quality of ServiceTyp. best effort, no guarantees (same as all 802.11 products)


Advantages/DisadvantagesAdvantage: free ISM band, compatible with 802.11b standardDisadvantage: heavy interference on ISM band, no service guarantees


WLAN: IEEE 802.11a

Data rate6, 9, 12, 18, 24, 36, 48, 54 Mbit/s, depending on SNRUser throughput (1500 byte packets): 5.3 (6), 18 (24), 24 (36), 32 (54) 6, 12, 24 Mbit/s mandatory

Transmission range100m outdoor, 10m indoore.g. 54 Mbit/s up to 5 m, 48 up to 12 m, 36 up to 25 m, 24 up to 30m, 18 up to 40 m, 12 up to 60 m

FrequencyFree 5.15-5.25, 5.25-5.35, 5.725-5.825 GHz ISM-band



AvailabilitySome products, some vendors


Quality of ServiceTyp. best effort, no guarantees (same as all 802.11 products)


Advantages/DisadvantagesAdvantage: fits into 802.x standards, free ISM band, available, simple system, uses less crowded 5 GHz bandDisadvantage: stronger shading due to higher frequency, no service guarantees


WLAN: IEEE 802.11h – Regulatory Details

Spectrum Managed 802.11a power controldyn. channel/frequency selection

4 frequency bands:

5.150 - 5.250 GHz 4 usable channels (100 MHz)indoor only max. 30mW EIRP (.11a)TPC (Transmit Power Control) max. 60mW EIRPcombined TPC and DCS/DFS (Dynamic Channel/Frequency Selection) max. 200mW EIRPTurbo Mode: combination of two carriers to reach 108 Mbps

5.250 - 5.350 GHz 4 usable channelsTPC, DCS/DFS mandatory

5.470 – 5.725 GHz indoor and outdoormax. 1W EIRPdisallowed in USnot supported by all chipsets

5.725 bis 5.825 GHz disallowed in Germany

EIRP (Equivalent Isotropic Radiated Power)

Usage in Germany according to the German Federal Regulation (Vorschrift derRegulierungsbehörde für das Telekommunikations- und Postwesen, RegTP, 35/2002)


IEEE 802.11a – PHY Frame Format

rate service payload

variable bits

6 Mbit/s

PLCP preamble signal data

symbols12 1 variable

reserved length tailparity tail pad

616611214 variable

6, 9, 12, 18, 24, 36, 48, 54 Mbit/s

PLCP header


Operating Channels for 802.11a / US U-NII

5150 [MHz]5180 53505200

36 44

16.6 MHz

center frequency = 5000 + 5*channel number [MHz]

channel40 48 52 56 60 64

149 153 157 161

5220 5240 5260 5280 5300 5320

5725 [MHz]5745 58255765

16.6 MHz

channel

5785 5805


OFDM in IEEE 802.11a (and HiperLAN2)

OFDM with 52 used subcarriers (64 in total)48 data + 4 pilot(plus 12 virtual subcarriers)312.5 kHz spacing

channel center frequency

subcarriernumber

1 7 21 26-26 -21 -7 -1

312.5 kHzpilot


IEEE 802.11a/b/g Data Rate

Barker: 11-bits Barker coding sequence (DPSK/DQPSK modulation, fixed code) CCK: Complementary Code Keying (DPSK/DQPSK modulation, switching of the spreading sequence)PBCC: Packet Binary Convolutional Code (8PSK, complex version of CCK))OFDM: Orthogonal Frequency Division Multiplexing (BPSK, QPSK, 16QAM, 64QAM)


WLAN: IEEE 802.11 – Extensions and developments (05/2007)

802.11d: Regulatory Domain Update – completed802.11e: MAC Enhancements – QoS – completed

Enhance the current 802.11 MAC to expand support for applications with Quality of Service requirements, and in the capabilities and efficiency of the protocol

802.11f: Inter-Access Point Protocol (IAPP) – withdrawn 2006Establish an Inter-Access Point Protocol for data exchange via the distribution system

802.11h: Spectrum Managed 802.11a (DCS, TPC) – completed 802.11i: Enhanced Security Mechanisms – completed

Enhance the current 802.11 MAC to provide improvements in security802.11j: MAC and PHY Specifications for Operation in 4.9-5 GHz Band in Japan –

completed802.11n: Throughput enhancement to 108-320 Mbps – draft

Study Groups5 GHz (harmonization ETSI/IEEE) – closed Radio Resource Measurements – startedHigh Throughput – started

See http://standards.ieee.org/getieee802/802.11.html for an update

http://standards.ieee.org/getieee802/802.11.html


WLAN: IEEE 802.11 – Details

802.11d aims to produce versions of 802.11b that work at other frequencies, making it suitable for parts of the world where the 2.4GHz band isn't available. Most countries have now released this band, thanks to an ITU recommendation and extensive lobbying by equipment manufacturers. The only holdout is Spain, which may follow soon.802.11e add QoS capabilities to 802.11 networks. It replaces the Ethernet-like MAC layer with a coordinated Time Division Multiple Access (TDMA) scheme, and adds extra error-correction to important traffic. The technology is similar to Whitecap, a proprietary protocol developed by Sharewave and used in Cisco's 802.11a prototypes. A standard was supposed to be finalized by the end of 2001, but has run into delays thanks to arguments over how many classes of service should be provided and exactly how they should be implemented. 802.11f tries to improve the handover mechanism in 802.11 so that users can maintain a connection while roaming between two different switched segments (radio channels), or between access points attached to two different networks. This is vital if wireless LANs are to offer the same mobility that cell phone users take for granted. 802.11h attempts to add better control over transmission power and radio channel selection to 802.11a. Along with 802.11e, this could make the standard acceptable to European regulators. 802.11i deals with 802.11's most obvious weakness: security. Rather than WEP, this is an entirely new standard based on the Advanced Encryption Standard (AES), the U.S. government's "official" encryption algorithm.


WLAN: IEEE 802.11 – More Details

IEEE 802.11 - THE WLAN STANDARD was original 1 Mbit/s and 2 Mb/s, 2.4 GHz RF and IR standard (1997), all the others listed below are Amendments to this standard, except for Recommended Practices 802.11F and 802.11T.

IEEE 802.11a - 54 Mbit/s, 5 GHz standard (1999, shipping products in 2001) IEEE 802.11b - Enhancements to 802.11 to support 5.5 and 11 Mb/s (1999) IEEE 802.11c - Bridge operation procedures; included in the IEEE 802.1D standard (2001) IEEE 802.11d - International (country-to-country) roaming extensions (2001) IEEE 802.11e - Enhancements: QoS, including packet bursting (2005) IEEE 802.11F - Inter-Access Point Protocol (2003) Withdrawn February 2006 IEEE 802.11g - 54 Mb/s, 2.4 GHz standard (backwards compatible with b) (2003) IEEE 802.11h - Spectrum Managed 802.11a (5 GHz) for European compatibility (2004) IEEE 802.11i - Enhanced security (2004) IEEE 802.11j - Extensions for Japan (2004) IEEE 802.11k - Radio resource measurement enhancements (proposed - 2007?) IEEE 802.11m - Maintenance of the standard; odds and ends. (ongoing) IEEE 802.11n - Higher throughput improvements using MIMO (multiple input, multiple output antennas)

(pre-draft - 2009?) IEEE 802.11p - WAVE - Wireless Access for the Vehicular Environment (such as ambulances and

passenger cars) (working - 2009?) IEEE 802.11r - Fast roaming Working "Task Group r" - 2007? IEEE 802.11s - ESS Extended Service Set Mesh Networking (working - 2008?) IEEE 802.11T - Wireless Performance Prediction (WPP) - test methods and metrics Recommendation

(working - 2008?) IEEE 802.11u - Interworking with non-802 networks (for example, cellular) (proposal evaluation - ?) IEEE 802.11v - Wireless network management (early proposal stages - ?) IEEE 802.11w - Protected Management Frames (early proposal stages - 2008?) IEEE 802.11y - 3650-3700 Operation in the U.S. (early proposal stages - ?)

http://en.wikipedia.org/wiki/802.11#802.11a

http://en.wikipedia.org/wiki/802.11#802.11b

http://en.wikipedia.org/wiki/IEEE_802.11c

http://en.wikipedia.org/wiki/IEEE_802.1D

http://en.wikipedia.org/wiki/IEEE_802.11d

http://en.wikipedia.org/wiki/IEEE_802.11e

http://en.wikipedia.org/wiki/Quality_of_service

http://en.wikipedia.org/wiki/IEEE_802.11F

http://en.wikipedia.org/wiki/Inter-Access_Point_Protocol

http://en.wikipedia.org/wiki/802.11#802.11g

http://en.wikipedia.org/wiki/IEEE_802.11h

http://en.wikipedia.org/wiki/IEEE_802.11i

http://en.wikipedia.org/wiki/IEEE_802.11j

http://en.wikipedia.org/wiki/IEEE_802.11k

http://en.wikipedia.org/wiki/IEEE_802.11m

http://en.wikipedia.org/wiki/802.11#802.11n

http://en.wikipedia.org/wiki/IEEE_802.11p

http://en.wikipedia.org/wiki/IEEE_802.11r

http://en.wikipedia.org/wiki/Roaming

http://en.wikipedia.org/wiki/IEEE_802.11s

http://en.wikipedia.org/wiki/Extended_Service_Set

http://en.wikipedia.org/wiki/IEEE_802.11T

http://en.wikipedia.org/wiki/IEEE_802.11u

http://en.wikipedia.org/wiki/IEEE_802.11v

http://en.wikipedia.org/wiki/Network_management

http://en.wikipedia.org/wiki/IEEE_802.11w

http://en.wikipedia.org/wiki/IEEE_802.11y


ReferenceBooks on 802.11:

Franz-Joachim Kauffels: Wireless LANs: Drahtlose Netze planen und verwirklichen, der Standard IEEE 802.11 im Detail, WLAN-Design und Sicherheitsrichtlinien. 1. Aufl., mitp-Verl., Bonn, 2002 Frank Ohrtman: WiFi-Handbook – Building 802.11b wireless networks. McGraw-Hill, 2003 Jochen Schiller: Mobile Communications (German and English), Kap 7.3, Addison-Wesley, 2002

Details on 802.11e:Anders Lindgren, Andreas Almquist, Olov Schelén. Quality of service schemes for IEEE 802.11 wireless LANs: an evaluation. Mobile Networks and Applications, Volume 8 Issue 3, June 2003Daqing Gu; Jinyun Zhang. QoS enhancement in IEEE 802.11 wireless local area networks. Communications Magazine, IEEE , Volume: 41 Issue: 6, June 2003 Qiu Qiang; Jacob, L., Radhakrishna Pillai, R., Prabhakaran, B.. MAC protocol enhancements for QoSguarantee and fairness over the IEEE 802.11 wireless LANs. 11th Intl. Conf. on Computer Communications and Networks, Oct. 2002 Mangold S, Choi S, May P, Klein O, Hiertz G, and Stibor L. IEEE 802.11e wireless LAN for quality of service. Proc. Of European Wireless (EW2002), Feb. 2002

Web Links:The IEEE 802.11 Wireless LAN Standardshttp://standards.ieee.org/getieee802/802.11.html

Introduction to the IEEE 802.11 Wireless LAN Standardhttp://www.wlana.org/learn/80211.htm

http://standards.ieee.org/getieee802/802.11.html

http://www.wlana.org/learn/80211.htm

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