IT351: Mobile & Wireless Computing Wireless Local Area Networks (WLAN) Part-1: IEEE802.11 Objectives: To provide a detailed study of the WLAN architecture and system operation

Outline 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 chapters Support for Mobility Chapter 9: Mobile Transport Layer Chapter 8: Mobile Network Layer Chapter 4: Telecommunication Systems Chapter 5: Satellite Systems Chapter 6: Broadcast Systems Chapter 7: Wireless LAN Chapter 3: Medium Access Control Chapter 2: Wireless Transmission

Mobile Communication Technology according to IEEE Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 Mobile Communication Technology according to IEEE WiFi 802.11a 802.11h Local wireless networks WLAN 802.11 802.11i/e/…/n/…/z/aa 802.11b 802.11g ZigBee 802.15.4 802.15.4a/b/c/d/e/f/g Personal wireless nw WPAN 802.15 802.15.5, .6 (WBAN) 802.15.3 802.15.3b/c 802.15.2 802.15.1 Bluetooth Wireless distribution networks WMAN 802.16 (Broadband Wireless Access) WiMAX + Mobility [802.20 (Mobile Broadband Wireless Access)] 802.16e (addition to .16 for mobile devices) Prof. Dr.-Ing. Jochen Schiller

Wireless LAN (WLAN) Main uses: Main Standard is IEEE 802.11 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

Characteristics of wireless LANs Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 Characteristics 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 Prof. Dr.-Ing. Jochen Schiller

Characteristics 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 LANs Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 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 (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 … Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 Classifications of transmission technologies: infrared 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 Prof. Dr.-Ing. Jochen Schiller

IEEE802.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 Bands

IEEE 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: infrastructure vs. ad-hoc networks Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 Classifications of IEEE802.11: infrastructure vs. ad-hoc networks infrastructure network AP: Access Point AP AP wired network AP ad-hoc network Prof. Dr.-Ing. Jochen Schiller

802.11 - System architecture infrastructure network Freie Universität Berlin Institut of Computer Science 802.11 - System architecture infrastructure network Mobile Communications 2002 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 802.11 LAN 802.x LAN STA1 BSS1 Portal Access Point Distribution System Access Point ESS BSS2 STA2 STA3 802.11 LAN Prof. Dr.-Ing. Jochen Schiller 9

IEEE802.11: System architecture infrastructure 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 architecture Ad-hoc network Freie Universität Berlin Institut of Computer Science 802.11 – System architecture Ad-hoc network Mobile Communications 2002 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 STA1 IBSS1 STA3 STA2 IBSS2 STA5 STA4 802.11 LAN Prof. Dr.-Ing. Jochen Schiller

IEEE802.11: Protocol architecture Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 IEEE802.11: Protocol architecture fixed terminal mobile terminal infrastructure network access point application application TCP TCP IP IP LLC LLC LLC 802.11 MAC 802.11 MAC 802.3 MAC 802.3 MAC 802.11 PHY 802.11 PHY 802.3 PHY 802.3 PHY Prof. Dr.-Ing. Jochen Schiller

802.11 – Protocol Architecture Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 802.11 – Protocol Architecture MAC access mechanisms, fragmentation, encryption MAC Management Association/de-association, synchronization, roaming, MIB (management Information Base), power management to save battery power, authentication mechanism 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) Station Management LLC DLC MAC MAC Management PLCP PHY Management PHY PMD Prof. Dr.-Ing. Jochen Schiller

802.11 - Physical layer (legacy) Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 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 Prof. Dr.-Ing. Jochen Schiller

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

Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 802.11 - 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 Prof. Dr.-Ing. Jochen Schiller

MAC 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

Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 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 DIFS DIFS PIFS SIFS medium busy contention next frame t direct access if medium is free  DIFS Prof. Dr.-Ing. Jochen Schiller

802.11 - CSMA/CA access method I Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 802.11 - 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) contention window (randomized back-off mechanism) DIFS DIFS medium busy next frame direct access if medium is free  DIFS t slot time (20µs) Prof. Dr.-Ing. Jochen Schiller 12

802.11 - competing stations - simple version Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 802.11 - competing stations - simple version DIFS DIFS DIFS DIFS boe bor boe bor boe busy station1 boe busy station2 busy station3 boe busy boe bor station4 boe bor boe busy boe bor station5 t busy medium not idle (frame, ack etc.) boe elapsed backoff time packet arrival at MAC bor residual backoff time Prof. Dr.-Ing. Jochen Schiller

802.11 – 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)

Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 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) DIFS data sender SIFS ACK receiver DIFS data other stations t waiting time contention Prof. Dr.-Ing. Jochen Schiller

802.11 – DFWMAC with RTS/CTS (method II) Freie Universität Berlin Institut of Computer Science 802.11 – DFWMAC with RTS/CTS (method II) Mobile Communications 2002 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) DIFS RTS data sender SIFS SIFS SIFS CTS ACK receiver DIFS NAV (RTS) data other stations NAV (CTS) t defer access contention Prof. Dr.-Ing. Jochen Schiller

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 Fragmentation Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 CTS/RTS with Fragmentation DIFS RTS frag1 frag2 sender SIFS SIFS SIFS SIFS SIFS CTS ACK1 ACK2 receiver NAV (RTS) NAV (CTS) DIFS NAV (frag1) data other stations NAV (ACK1) t contention Prof. Dr.-Ing. Jochen Schiller

DFWMAC-PCF with polling – Method III (almost never used) Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 DFWMAC-PCF with polling – Method III (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. Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 DFWMAC-PCF (cont.) PIFS stations‘ NAV wireless stations point coordinator D1 U1 SIFS D2 U2 SuperFrame t0 medium busy t1 t stations‘ NAV wireless stations point coordinator D3 PIFS D4 U4 SIFS CFend contention period contention free period t2 t3 t4 Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 802.11 - 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 bytes 2 2 6 6 6 2 6 0-2312 4 Frame Control Duration/ ID Address 1 Address 2 Address 3 Sequence Control Address 4 Data CRC bits 2 2 4 1 1 1 1 1 1 1 1 Protocol version Type Subtype To DS From DS More Frag Retry Power Mgmt More Data WEP Order Prof. Dr.-Ing. Jochen Schiller

802.11 - 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 bytes 2 2 6 6 6 2 6 0-2312 4 Frame Control Duration/ ID Address 1 Address 2 Address 3 Sequence Control Address 4 Data CRC bits 2 2 4 1 1 1 1 1 1 1 1 Protocol version Type Subtype To DS From DS More Frag Retry Power Mgmt More Data WEP Order

Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 MAC address format DS: Distribution System AP: Access Point DA: Destination Address SA: Source Address BSSID: Basic Service Set Identifier RA: Receiver Address TA: Transmitter Address Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 802.11 - 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 Prof. Dr.-Ing. Jochen Schiller

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) Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 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) B B B B access point busy busy busy busy medium t B value of the timestamp beacon frame Prof. Dr.-Ing. Jochen Schiller

Synchronization using a Beacon (ad-hoc) Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 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 beacon interval B1 B1 station1 B2 B2 station2 busy busy busy busy medium t B value of the timestamp beacon frame random delay Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 Power 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 Prof. Dr.-Ing. Jochen Schiller

Power 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 (infrastructure) Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 Power saving with wake-up patterns (infrastructure) TIM interval DTIM interval D B T T d D B access point busy busy busy busy medium p d station t T TIM D DTIM awake d data transmission to/from the station B broadcast/multicast p PS poll Prof. Dr.-Ing. Jochen Schiller

Power saving with wake-up pattern (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

Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 802.11 - 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 Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 WLAN: 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 Prof. Dr.-Ing. Jochen Schiller

Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 WLAN: 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 Prof. Dr.-Ing. Jochen Schiller

WLAN: IEEE 802.11– current developments Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 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 Prof. Dr.-Ing. Jochen Schiller

WLAN: IEEE 802.11– current developments Freie Universität Berlin Institut of Computer Science Mobile Communications 2002 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/ Prof. Dr.-Ing. Jochen Schiller