technische universitÄt ilmenau ieee 802...basic service set (bss): group of stations using the same...
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TECHNISCHE UNIVERSITÄTILMENAU
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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)
Wireless Internet 3Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 4Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 5Andreas Mitschele-Thiel 9-Sep-07
Comparison: Infrastructure vs. Ad-hoc Networks
infrastructurenetwork
ad-hoc network
APAP
AP
wired network
AP: Access Point
Wireless Internet 6Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 7Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 8Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 9Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 10Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 11Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 12Andreas Mitschele-Thiel 9-Sep-07
DSSS PHY Packet Format
synchronization SFD signal service HEC payload
PLCP preamble PLCP header
128 16 8 8 16 variable bits
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
Wireless Internet 13Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 14Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 15Andreas Mitschele-Thiel 9-Sep-07
802.11 – Timing DetailsTransmission and Processing Delays
Times for 802.11aSlotTime – 9 μsSIFS – 16 μsPIFS – 25 μsDIFS – 34 μs
Wireless Internet 16Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 17Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 18Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 19Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 20Andreas Mitschele-Thiel 9-Sep-07
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)
Wireless Internet 21Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 22Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 23Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 24Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 25Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 26Andreas Mitschele-Thiel 9-Sep-07
Control Frames: ACK, RTS, CTS
Acknowledgement
Request To Send
Clear To Send
FrameControl Duration Receiver
AddressTransmitter
Address CRC
2 2 6 6 4bytes
FrameControl Duration Receiver
Address CRC
2 2 6 4bytes
FrameControl Duration Receiver
Address CRC
2 2 6 4bytes
ACK
RTS
CTS
Duration is used to determine NAV value
Wireless Internet 27Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 28Andreas Mitschele-Thiel 9-Sep-07
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!
Wireless Internet 29Andreas Mitschele-Thiel 9-Sep-07
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)
Wireless Internet 30Andreas Mitschele-Thiel 9-Sep-07
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?)
Wireless Internet 31Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 32Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 33Andreas Mitschele-Thiel 9-Sep-07
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)
Wireless Internet 34Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 35Andreas Mitschele-Thiel 9-Sep-07
IEEE 802.11b – PHY Frame Formats
synchronization SFD signal service HEC payload
PLCP preamble PLCP header
128 16 8 8 16 variable bits
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)
56 16 8 8 16 variable bits
length16
96 µs 2, 5.5 or 11 Mbit/s
Long PLCP PPDU format 8 (corresponds to 802.11)
Short PLCP PPDU format (optional)
Wireless Internet 36Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 37Andreas Mitschele-Thiel 9-Sep-07
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)
SecurityLimited, WEP insecure, SSID
Cost50€ adapter, 200€ base station
AvailabilitySome products, some vendors
Connection set-up timeConnectionless/always on
Quality of ServiceTyp. best effort, no guarantees (same as all 802.11 products)
ManageabilityLimited (no automated key distribution, sym. encryption)
Advantages/DisadvantagesAdvantage: free ISM band, compatible with 802.11b standardDisadvantage: heavy interference on ISM band, no service guarantees
Wireless Internet 38Andreas Mitschele-Thiel 9-Sep-07
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
SecurityLimited, WEP insecure, SSID
Cost100€ adapter, 200€ base station
AvailabilitySome products, some vendors
Connection set-up timeConnectionless/always on
Quality of ServiceTyp. best effort, no guarantees (same as all 802.11 products)
ManageabilityLimited (no automated key distribution, sym. encryption)
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
Wireless Internet 39Andreas Mitschele-Thiel 9-Sep-07
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)
Wireless Internet 40Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 41Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 42Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 43Andreas Mitschele-Thiel 9-Sep-07
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)
Wireless Internet 44Andreas Mitschele-Thiel 9-Sep-07
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
Wireless Internet 45Andreas Mitschele-Thiel 9-Sep-07
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.
Wireless Internet 46Andreas Mitschele-Thiel 9-Sep-07
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 - ?)
Wireless Internet 47Andreas Mitschele-Thiel 9-Sep-07
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
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