Wireless Local Area Networks (WLAN)Wireless Local Area Networks (WLAN)Part-1: IEEE802.11Part-1: IEEE802.11

IT351: Mobile & Wireless ComputingIT351: Mobile & Wireless Computing

Objectives:– To provide a detailed study of the WLAN architecture and system operation

OutlineOutline

• Wireless LAN main uses, advantages, disadvantages• Classification of transmission technologies for WLAN• Classification of WLAN IEEE802.11

– Infrastructure networks

– Ad Hoc networks

• WLAN IEEE802.11– Architecture

– Protocols

– Physical layer

– MAC layer

– MAC management

– IEEE802.11-a/ b/... n

Overview of the main chaptersOverview of the main chapters

Chapter 2: Wireless Transmission

Chapter 3: Medium Access Control

Chapter 4: Telecommunication Systems

Chapter 5: Satellite Systems

Chapter 6: Broadcast Systems

Chapter 7: Wireless LAN

Chapter 8: Mobile Network Layer

Chapter 9: Mobile Transport Layer

Chapter 10: Support for Mobility

Mobile Communication Technology according to Mobile Communication Technology according to IEEE IEEE

Local wireless networksWLAN 802.11

802.11a

802.11b

802.11i/e/…/n/…/z/aa

802.11g

WiFi802.11h

Personal wireless nwWPAN 802.15

802.15.4

802.15.1802.15.2

Bluetooth

802.15.4a/b/c/d/e/f/gZigBee

802.15.3

Wireless distribution networksWMAN 802.16 (Broadband Wireless Access)

[802.20 (Mobile Broadband Wireless Access)]802.16e (addition to .16 for mobile devices)

+ Mobility

WiMAX

802.15.3b/c

802.15.5, .6 (WBAN)

Wireless LAN (WLAN)Wireless LAN (WLAN)

• Main uses:– Extension to existing

LAN– Cross building

interconnect– Nomadic access /

‘wireless hotspots’– Ad Hoc networks

• Main Standard is IEEE 802.11

• Wireless extension for Ethernet

• Wi-Fi, Wireless-Fidelity, Alliance to certify products to the IEEE standard

Distribution System

BSS1

BSS2 BSS3

BSS4

IBSS

ESS

Distribution System

BSS1

BSS2 BSS3

BSS4

IBSS

ESS

Characteristics of wireless LANsCharacteristics of wireless LANs

• Advantages– very flexible within the reception area,

– allow for design of small independent devices (e.g. to be put in pockets)

– Ad-hoc networks without previous planning possible

– (almost) no wiring difficulties (e.g. historic buildings, firewalls)

– more robust against disasters like, e.g., earthquakes, fire - or users pulling a plug...

– Cost is independent of the number of users

Characteristics of wireless LANsCharacteristics of wireless LANs

• Disadvantages– typically very low bandwidth compared to wired

networks (1-10 Mbit/s) due to shared medium

– high error rates, low quality

– many proprietary solutions, especially for higher bit-rates, standards take their time (e.g. IEEE 802.11n)

– products have to follow many national restrictions if working wireless, it takes a very long time to establish global solutions

– Safety & security

Design goals for wireless LANsDesign 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 (plug & play)• 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

• …

Classifications of transmission technologies: Classifications of transmission technologies: infrared vs. radio transmissioninfrared vs. radio transmission

• Infrared– At 900 nm wavelength, uses IR

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

• Advantages– simple, cheap, available in many

mobile devices– no licenses needed– simple shielding possible

• Disadvantages– interference by sunlight, heat

sources etc.– many things shield or absorb IR

light , can not penetrate objects– low bandwidth (115kbps – 4 Mbps

• Example– IrDA (Infrared Data Association)

interface available everywhere

• Radio– typically using the license free

ISM band at 2.4 GHz

• Advantages– experience from wireless WAN

and mobile phones can be used

– coverage of larger areas possible (radio can penetrate walls, furniture etc.)

• Disadvantages– very limited license free

frequency bands – shielding more difficult,

interference with other electrical devices

• Example– Many different products

IEEE802.x standardsIEEE802.x standards

• 802 standards specify OSI layers 1 & 2– Physical layer

• Encoding/decoding signals• Preamble (for synchronization)• Bit transmission/reception

– Link layer (Medium Access Control (MAC))• Manage access to media• Assemble/disassemble frames• Addressing and error detection• Interface with higher layers

ISM Unlicensed Frequency BandsISM Unlicensed Frequency Bands

IEEE 802.11 WLANIEEE 802.11 WLAN– 802.11 (Legacy, 1997) operates at 1-2

Mbps, with 3 methods• 1 infrared• 2 radio access (FHSS, DSSS)

– 802.11a (1999) operates at 54Mbps (5GHz Freq. Band)

– 802.11b (Wi-Fi 1999) operates at 11Mbps (2.4GHz ISM Freq. Band - 2.400 – 2.4835 GHz)

– 802.11g (2003) operates at 54Mbps (2.4GHz Freq. Band)

– 802.11n (Oct 2009) operates at 540 M bps (typically 200Mbps) (2.4GHz or 5GHz Freq. Band)

Wireless Communications and Networks, W. Stallings, Prentice Hall, N.J., 2001.

• Two Modes:

– Infrastructure Mode (LAN extension)

– Ad Hoc (wireless only)

Classifications of IEEE802.11:Classifications of IEEE802.11: infrastructure vs. ad-hoc networks infrastructure vs. ad-hoc networksinfrastructure network

ad-hoc network

APAP

AP

wired network

AP: Access Point

802.11 - System architecture 802.11 - System architecture infrastructure network infrastructure network

• 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 Point– station integrated into the wireless

LAN and the distribution system

• Portal– bridge to other (wired) networks

• Distribution System– interconnection network to form one

logical network (ESS: Extended Service Set) based on several BSS

– Each ESS has its own identifier ESSID

Distribution System

Portal

802.x LAN

Access Point

802.11 LAN

BSS2

802.11 LAN

BSS1

Access Point

STA1

STA2 STA3

ESS

IEEE802.11: System architecture IEEE802.11: System architecture infrastructure networkinfrastructure network

• The distribution system is not specified in IEEE802.11. – It could consist of IEEE LANs, wireless links or any other

networks

– It handles data transfer between different APs

– To participate in a WLAN, you need to know the ESSID

• Stations can select an AP and associate with it– The AP supports roaming (changing access points)

– APs provide synchronization within a BSS, support power management, and can control medium access

802.11 – System architecture802.11 – System architectureAd-hoc networkAd-hoc network

• Direct communication within a limited range– Station (STA):

terminal with access mechanisms to the wireless medium

– Independent Basic Service Set (IBSS):group of stations using the same radio frequency

– No specific node for data routing, or forwarding or exchange of topology information

802.11 LAN

IBSS2

802.11 LAN

IBSS1

STA1

STA4

STA5

STA2

STA3

IEEE802.11: Protocol architectureIEEE802.11: Protocol architecture

mobile terminal

access point

fixedterminal

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

infrastructurenetwork

LLC LLC

802.11 – Protocol Architecture802.11 – Protocol Architecture• PLCP Physical Layer Convergence Protocol

– clear channel assessment signal (carrier sense)

– Service access point (SAP)

• PMD Physical Medium Dependent

– modulation, coding

• PHY Management– channel selection, MIB maintenance

• Station Management– coordination of all management functions,

higher layer functions (interaction with distribution system)

PMD

PLCP

MAC

LLC

MAC Management

PHY Management

• MAC– access mechanisms, fragmentation,

encryption

• MAC Management– Association/de-association,

synchronization, roaming, MIB (management Information Base), power management to save battery power, authentication mechanism

PH

YD

LC

Sta

tion

Man

agem

ent

802.11 - Physical layer (legacy)802.11 - Physical layer (legacy)

• 3 versions: 2 radio (typ. 2.4 GHz ISM), 1 IR– data rates 1 or 2 Mbit/s

• All physical variants include the provision of the clear channel assessment (CCA). This is needed for MAC mechanisms.

• The Physical layer a service access point (SAP) with 1 or 2 Mbits/s transfer rate to the MAC layer.

• FHSS (Frequency Hopping Spread Spectrum)– spreading, despreading using different hopping sequences (79

hopping channels for North America and Europe)

– Frequency Shift Keying (FSK) digital modulation

802.11 - Physical layer (legacy)802.11 - Physical layer (legacy)

• DSSS (Direct Sequence Spread Spectrum)– Spreading, despreading using 11-chip Barker code

chipping sequence: +1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1

– Phase Shift Keying (PSK) digital modulation

– max. radiated power 1 W (USA), 100 mW (EU), min. 1mW

– Robust against interference and multipath propagation

– More complex compared to FHSS

• Infrared– 850-950 nm, diffuse light, typ. 10 m range

– Typically in buildings (classrooms, meeting rooms,..)

– Frequency reuse is simple, a wall is enough for shielding

802.11 - MAC layer - DFWMAC802.11 - MAC layer - DFWMAC• The MAC mechanisms are called Distributed Foundation

Wireless Medium Access Control (DFWMAC) • Functions: medium access, support for roaming, authentication

and power conservation• Traffic services

– Asynchronous Data Service (mandatory)• exchange of data packets based on “best-effort” – no delay

bounds• support of broadcast and multicast• Implemented using distributed coordination function (DCF) OR

Point Coordination Function (PCF)• For both infrastructure and ad Hoc

– Time-Bounded Service (optional)• implemented using PCF (Point Coordination Function)• Provides delay guarantees • For infrastructure 802.11 only

MAC LayerMAC Layer

• Asynchronous Data Service access method– DFWMAC-DCF CSMA/CA (mandatory)

• collision avoidance via randomized „back-off“ mechanism

• minimum distance between consecutive packets• ACK packet for acknowledgements (not for broadcasts)

– DFWMAC-DCF w/ RTS/CTS (optional)• avoids hidden terminal problem

– DFWMAC-PCF (optional)

• Time-bounded Service access method– DFWMAC- PCF (optional)

• access point polls terminals according to a list

802.11 - MAC layer 802.11 - MAC layer • Priorities

– defined through different inter frame spaces

– no guaranteed, hard priorities

– SIFS (Short Inter Frame Spacing)• highest priority, for ACK, CTS, polling response

– PIFS (PCF IFS)• medium priority, for time-bounded service using PCF

– DIFS (DCF, Distributed Coordination Function IFS)• lowest priority, for asynchronous data service

t

medium busySIFS

PIFS

DIFSDIFS

next framecontention

direct access if medium is free DIFS

t

medium busy

DIFSDIFS

next frame

contention window(randomized back-offmechanism)

802.11 - CSMA/CA access method I802.11 - CSMA/CA access method I• 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 a DCF Inter-Frame Space (DIFS), the station can start sending

• 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 time (20µs)direct access if medium is free DIFS

802.11 - competing stations - simple 802.11 - competing stations - simple versionversion

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

DIFSboebusy

boe

boe

bor

bor

802.11 – CSMA/CA802.11 – CSMA/CA

• The contention window (CW) size affect the performance of the MAC scheme

• A small CW ensures shorter access delay but the probability of collision increases (more than one station can have the same backoff time)

• The contention window starts with a minimum value then doubles each time a collision occurs up to a maximum value (e.g. 7, 15, 31,63, 127, 255).

• This is called the exponential backoff algorithm (already used in CSMA/CD)

802.11 - CSMA/CA 802.11 - CSMA/CA • Sending unicast packets

– station has to wait for DIFS before sending data

– receivers acknowledge at once (after waiting for SIFS) if the packet was received correctly (CRC)

– automatic retransmission of data packets in case of transmission errors (The sender has to compete again)

t

SIFS

DIFS

data

ACK

waiting time

otherstations

receiver

senderdata

DIFS

contention

802.11 – DFWMAC with RTS/CTS (method II)802.11 – DFWMAC with RTS/CTS (method II)• Sending unicast packets

– To solve the problem of hidden terminal

– station 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 ACK

– other stations store medium reservations distributed via RTS and CTS in the NAV (net allocation vector)

t

SIFS

DIFS

data

ACK

defer access

otherstations

receiver

senderdata

DIFS

contention

RTS

CTSSIFS SIFS

NAV (RTS)NAV (CTS)

802.11 – DFWMAC with RTS/CTS (cont.)802.11 – DFWMAC with RTS/CTS (cont.)

• The scheme reserves the medium for one user (virtual reservation scheme)

• RTS/CTS can result in a non-negligible overhead causing a waste of bandwidth and higher delay

• A threshold based on frame size can be used to determine when to use the additional mechanism and when to disable it

• To reduce the bit error-rates in transmission, fragmentation can be used. However, for RTS/CTS scheme all fragments are sent by one RTS. Each fragment reserve the medium for the next fragment.

CTS/RTS with FragmentationCTS/RTS with Fragmentation

t

SIFS

DIFS

data

ACK1

otherstations

receiver

senderfrag1

DIFS

contention

RTS

CTSSIFS SIFS

NAV (RTS)NAV (CTS)

NAV (frag1)NAV (ACK1)

SIFSACK2

frag2

SIFS

DFWMAC-PCF with polling – Method III DFWMAC-PCF with polling – Method III (almost never used)(almost never used)

• The two previous methods cannot guarantee a maximum delay or minimum bandwidth

• PCF provides time-bounded service• It requires an access point that control medium access and

polls the single nodes • Ad Hoc network can’t use this function so it provides only best-

effort service• The point coordinator in the access point splits the access time

into super frame periods.• A super frame comprises an contention-free period and a

contention period• If only PCF is used and polling is distributed evenly, the

bandwidth is also distributed evenly – static centrally controlled TDMA with TDD transmission

• Much overhead if nodes have nothing to send.

DFWMAC-PCF (cont.)DFWMAC-PCF (cont.)

tstations‘NAV

wirelessstations

point coordinator

D3

NAV

PIFSD4

U4

SIFS

SIFSCFend

contentionperiod

contention free period

t2 t3 t4

PIFS

stations‘NAV

wirelessstations

point coordinator

D1

U1

SIFS

NAV

SIFSD2

U2

SIFS

SIFS

SuperFramet0

medium busy

t1

802.11 - Frame format802.11 - Frame format• Types: control frames, management frames, data frames• Sequence numbers

– important against duplicated frames due to lost ACKs

• Addresses– receiver, transmitter (physical), BSS identifier, sender/receiver

(logical)

• Miscellaneous– Duration (to set the NAV), checksum, frame control, data

FrameControl

Duration/ID

Address1

Address2

Address3

SequenceControl

Address4

Data CRC

2 2 6 6 6 62 40-2312bytes

Protocolversion

Type SubtypeToDS

MoreFrag

RetryPowerMgmt

MoreData

WEP

2 2 4 1

FromDS

1

Order

bits 1 1 1 1 1 1

802.11 - Frame format802.11 - Frame format• Frame Control

– Protocol version: 2 bits

– Type (management 00, control 01, data 10)

– Subtype (e.g. Management- association 0000, beacon 100 Control – RTS 1011, CTS 1100)

– More fragments: 1 if another fragment to follow

– Retry: 1 if retransmission of an earlier frame

– Power Management: 1 if the station will go to power save mode

– More Data: A sender has more data to send

– Wired Equivalent Privacy (WEP): Standard security mechanism applied

– Order: frame must be processed in strict order

FrameControl

Duration/ID

Address1

Address2

Address3

SequenceControl

Address4

Data CRC

2 2 6 6 6 62 40-2312bytes

Protocolversion

Type SubtypeToDS

MoreFrag

RetryPowerMgmt

MoreData

WEP

2 2 4 1

FromDS

1

Order

bits 1 1 1 1 1 1

MAC address formatMAC 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 SystemAP: Access PointDA: Destination AddressSA: Source AddressBSSID: Basic Service Set IdentifierRA: Receiver AddressTA: Transmitter Address

802.11 - MAC management802.11 - MAC management

MAC management plays a central role in an IEEE802.11 as it controls all the functions related to system integration, i.e., integration of a wireless station into a BSS, formation of an ESS, synchronization of stations,..etc

The major functions are:

• Synchronization– try to find a WLAN and stay within it– synchronization of internal clock (timing synchronization

function (TSF)• For power management• For coordination of PCF (super frame)• For synchronization of hopping sequence in FHSS systems

– Generation of beacon signals

802.11 - MAC management (cont.)802.11 - MAC management (cont.)

• Power management– To control transmitter activity for power conservation

– sleep-mode without missing a frame

– periodic sleep, frame buffering, traffic measurements

• Association/Re-association– integration into a WLAN

– roaming, i.e. change networks by changing access points

– scanning, i.e. active search for a network

• MIB - Management Information Base– managing, read, write, update

Synchronization using a Beacon (infrastructure)Synchronization using a Beacon (infrastructure)• Within a BSS, timing is conveyed by the periodic transmission of a beacon

frame• A beacon contains a timestamp and other management information

(identification of BSS, power management, roaming)• In infrastructure-based networks, the beacon is sent by the access point

periodically. However, it may be delayed if medium is busy, but beacon interval is not shifted if one beacon is delayed.

• The time stamp is used by a node to adjust its local clock

beacon interval(20ms – 1s)

tmedium

accesspoint

busy

B

busy busy busy

B B B

value of the timestamp B beacon frame

Synchronization using a Beacon (ad-hoc)Synchronization using a Beacon (ad-hoc)

• Each node maintains its own timer and starts transmission of a beacon frame after the beacon interval

• Using random backoff algorithm, one beacon only wins

• All other stations adjust their internal clock according to the received beacon

tmedium

station1

busy

B1

beacon interval

busy busy busy

B1

value of the timestamp B beacon frame

station2

B2 B2

random delay

Power managementPower management• Power-saving mechanisms are crucial for wireless

devices• Standard WLAN protocols assume that stations are

always ready to receive data. This permanent readiness consumes much power

• Idea: switch the transceiver off if not needed• States of a station: sleep and awake• Timing Synchronization Function (TSF)

– stations wake up periodically at the same time

• Buffering of data at senders• Senders announce destination during wake periods • Longer off periods save battery life but reduce

average throughput and increase delay

Power ManagementPower Management• Infrastructure

– Access point buffers all frames destined for stations operating in power-save mode

– With every beacon sent, a Traffic Indication Map (TIM) is transmitted• TIM contains a list of unicast receivers transmitted by AP• Beacon interval = TIM interval

– Additionally, the AP maintains a Delivery Traffic Indication Map (DTIM)• list of broadcast/multicast receivers transmitted by AP• DTIM interval = multiple of TIM interval

– The TSF assures that sleeping stations will wake-up periodically and listen to the beacon and TIM

– If TIM indicates a unicast frame buffered for a station, the station stay awake to receive it

– Stations always stay awake for muti-cast/ broadcast transmission

– Stations also wake-up when they have frames to be transmitted

Power saving with wake-up patterns Power saving with wake-up patterns (infrastructure)(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

Power saving with wake-up pattern Power saving with wake-up pattern (Ad hoc)(Ad hoc)

• Ad-hoc– Ad-hoc Traffic Indication Map (ATIM)

• announcement of receivers by stations buffering frames• more complicated - no central AP• collision of ATIMs possible (scalability?)

• APSD (Automatic Power Save Delivery)– new method in 802.11e replacing above schemes

802.11 - Roaming802.11 - Roaming• No or bad connection? Then perform:• Scanning

– scan the environment,• Passive scanning: listen into the medium for beacon signals • Active scanning: send probes into the medium and wait for an answer

• Reassociation Request– Choose best AP (e.g. based on signal strength)– station sends a request to one or several AP(s)

• Reassociation Response– success: AP has answered, station can now participate– failure: continue scanning

• AP accepts Reassociation Request– signal the new station to the distribution system– the distribution system updates its data base (i.e., location information)– typically, the distribution system now informs the old AP so it can

release resources

• Fast roaming – 802.11r– e.g. for vehicle-to-roadside networks

WLAN: IEEE 802.11bWLAN: IEEE 802.11b• Data rate

– 1, 2, 5.5, 11 Mbit/s, depending on SNR

– User data rate max. approx. 6 Mbit/s

• Transmission range– 300m outdoor, 30m indoor

– Max. data rate ~10m indoor

• Frequency– DSSS, 2.4 GHz ISM-band

• Security– Limited, WEP insecure, SSID

(service set identifier)

• Availability– Many products, many vendors

• Connection set-up time– Connectionless/always on

• Quality of Service– Typ. Best effort, no guarantees

(unless polling is used, limited support in products)

• Manageability– Limited (no automated key

distribution, sym. Encryption)

• Special Advantages/Disadvantages– Advantage: many installed systems,

lot of experience, available worldwide, free ISM-band, many vendors, integrated in laptops, simple system

– Disadvantage: heavy interference on ISM-band, no service guarantees, slow relative speed only

WLAN: IEEE 802.11aWLAN: IEEE 802.11a• Data rate

– 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s, depending on SNR

– User throughput (1500 byte packets): 5.3 (6), 18 (24), 24 (36), 32 (54)

– 6, 12, 24 Mbit/s mandatory

• Transmission range– 100m outdoor, 10m indoor

• E.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

• Frequency– Free 5.15-5.25, 5.25-5.35, 5.725-

5.825 GHz ISM-band

• Security– Limited, WEP insecure, SSID

• Availability– Some products, some vendors

• Connection set-up time– Connectionless/always on

• Quality of Service– Typ. best effort, no guarantees

(same as all 802.11 products)

• Manageability– Limited (no automated key

distribution, sym. Encryption)

• Special Advantages/Disadvantages– Advantage: fits into 802.x standards,

free ISM-band, available, simple system, uses less crowded 5 GHz band

– Disadvantage: stronger shading due to higher frequency, no QoS

WLAN: IEEE 802.11– current developments WLAN: IEEE 802.11– current developments

• 802.11j: Extensions for operations in Japan– Changes of 802.11a for operation at 5GHz in Japan using only half the channel width at larger

range• 802.11-2007: Current “complete” standard

– Comprises amendments a, b, d, e, g, h, i, j• 802.11k: Methods for channel measurements

– Devices and access points should be able to estimate channel quality in order to be able to choose a better access point of channel

• 802.11m: Updates of the 802.11-2007 standard• 802.11n: Higher data rates above 100Mbit/s

– Changes of PHY and MAC with the goal of 100Mbit/s at MAC SAP– MIMO antennas (Multiple Input Multiple Output), up to 600Mbit/s are currently feasible– However, still a large overhead due to protocol headers and inefficient mechanisms

• 802.11p: Inter car communications– Communication between cars/road side and cars/cars– Planned for relative speeds of min. 200km/h and ranges over 1000m– Usage of 5.850-5.925GHz band in North America

• 802.11r: Faster Handover between BSS– Secure, fast handover of a station from one AP to another within an ESS– Current mechanisms (even newer standards like 802.11i) plus incompatible devices from

different vendors are massive problems for the use of, e.g., VoIP in WLANs– Handover should be feasible within 50ms in order to support multimedia applications efficiently

WLAN: IEEE 802.11– current developments WLAN: IEEE 802.11– current developments

• 802.11s: Mesh Networking– Design of a self-configuring Wireless Distribution System (WDS) based on 802.11– Support of point-to-point and broadcast communication across several hops

• 802.11T: Performance evaluation of 802.11 networks– Standardization of performance measurement schemes

• 802.11u: Interworking with additional external networks• 802.11v: Network management

– Extensions of current management functions, channel measurements– Definition of a unified interface

• 802.11w: Securing of network control– Classical standards like 802.11, but also 802.11i protect only data frames, not the

control frames. Thus, this standard should extend 802.11i in a way that, e.g., no control frames can be forged.

• 802.11y: Extensions for the 3650-3700 MHz band in the USA• 802.11z: Extension to direct link setup• 802.11aa: Robust audio/video stream transport• 802.11ac: Very High Throughput <6Ghz• 802.11ad: Very High Throughput in 60 GHz

• Note: Not all “standards” will end in products, many ideas get stuck at working group level

• Info: www.ieee802.org/11/, 802wirelessworld.com, standards.ieee.org/getieee802/