9/29/08 Wireless LANs
9/29/08Wireless LANs Characteristics IEEE 802.11 (PHY, MAC, Roaming, .11a, b, g, h, i, n z) Bluetooth / IEEE 802.15.x IEEE 802.16/.20/.21/.22 RFID ComparisonMobile Communication Technologyaccording to IEEE (examples)Local wireless networksWLAN 802.11WiFi802.11a802.11h802.11i/e/ /n/ /z802.11b802.11gZigBeePersonal wireless netsWPAN .15.5, .6 (WBAN)802.15.3802.15.3b/cBluetoothWireless distribution networksWMAN 802.16 (Broadband Wireless Access)WiMAX Mobility[802.20 (Mobile Broadband Wireless Access)]802.16e (addition to .16 for mobile devices)Characteristics of wireless LANs Advantages very flexible within the reception areaad-hoc networks without previous planning possible(almost) no wiring difficulties (e.g., historic buildings)more robust against disasters like, e.g., earthquakes, fire - or userspulling a plug.cheap (additional users don’t increase cost) Disadvantages typically very low bandwidth compared to wired networks(1-10 Mbit/s) due to shared medium, more interferencesmany proprietary solutions, especially for higher bit-rates, standardstake their time (e.g., IEEE 802.11n)products have to follow many national regulations, takes time forglobal solutions (IMT-2000).safety/security1
9/29/08Design goals for wireless LANsglobal, seamless operationlow power for battery useno special permissions or licenses needed to use the LANrobust transmission technologysimplified spontaneous cooperation at meetingseasy to use for everyone, simple managementprotection of investment in wired networkssecurity (no one should be able to read my data), privacy (no oneshould 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 interference by sunlight, heatsources, etc.many things shield or absorb IRlightlow bandwidthexperience from wireless WAN andmobile phones can be usedcoverage of larger areas possible(radio can penetrate walls, furnitureetc.)higher transmission ratesDisadvantages typically using the license free ISMband at 2.4 GHzAdvantages Example Radio simple, cheap, available in manymobile devicesno licenses neededsimple shielding possibleDisadvantages uses IR diodes, diffuse light,multiple reflections (walls, furniture,etc.)Advantages Infrared very limited license free frequencybandsshielding more difficult, interferencewith other electrical devicesExample many different productsIrDA (Infrared Data Association)interface available everywhereComparison: infrastructure vs. ad-hocnetworksinfrastructurenetworkAPAPwired networkAP: Access PointAPad-hoc network2
9/29/08802.11 - Architecture of aninfrastructure network 802.11 LAN STA1Station (STA) 802.x LANBasic Service Set (BSS) BSS1PortalAccessPoint AccessPointESSSTA2bridge to other (wired) networksDistribution System 802.11 LANstation integrated into the wirelessLAN and the distribution systemPortal BSS2group of stations using the sameradio frequencyAccess Point Distribution Systemterminal with access mechanismsto the wireless medium and radiocontact to the access pointinterconnection network to form onelogical network (EES: ExtendedService Set) basedon several BSSSTA3802.11 - Architecture of an ad-hoc network Direct communication within alimited range802.11 LAN STA1STA3IBSS1 STA2Station (STA):terminal with accessmechanisms to the wirelessmediumIndependent Basic Service Set(IBSS):group of stations using thesame radio frequencyIBSS2STA5STA4802.11 LANIEEE standard 802.11fixedterminalmobile terminalinfrastructurenetworkaccess pointapplicationapplicationTCPTCPIPIPLLCLLC802.11 MAC802.11 MAC 802.3 MACLLC802.3 MAC802.11 PHY802.11 PHY802.3 PHY802.3 PHY3
9/29/08802.11 - Layers and functions MAC PLCP Physical Layer ConvergenceProtocolaccess mechanisms,fragmentation, encryption MAC Management clear channel assessmentsignal (carrier sense) PMD Physical Medium Dependentsynchronization, roaming, MIB,power management modulation, coding PHY Management channel selection, MIB Station ManagementStation ManagementPHYDLC LLCMACMAC ManagementPLCPPHY ManagementPMDcoordination of all managementfunctions802.11 - Physical layer 3 versions: 2 radio (typ. 2.4 GHz), 1 IR data 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), GFSK modulation DSSS (Direct Sequence Spread Spectrum) DBPSK modulation for 1 Mbit/s (Differential Binary Phase ShiftKeying), 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 (Barkercode)max. radiated power 1 W (USA), 100 mW (EU), min. 1mW Infrared 850-950 nm, diffuse light, typ. 10 m rangecarrier detection, energy detection, synchronizationFHSS PHY packet format Synchronization synch with 010101. pattern SFD (Start Frame Delimiter) 0000110010111101 start pattern PLW (PLCP PDU Length Word) length of payload incl. 32 bit CRC of payload, PLW 4096 PSF (PLCP Signaling Field) data of payload (1 or 2 Mbit/s) HEC (Header Error Check) CRC with x16 x12 x5 180synchronization1612416SFDPLWPSFHECPLCP preamblevariablebitspayloadPLCP header4
9/29/08DSSS PHY packet format Synchronization future use, 00: 802.11 compliantLength data rate of the payload (0A: 1 Mbit/s DBPSK; 14: 2 Mbit/s DQPSK)Service 1111001110100000Signal synch., energy detection, frequency offset compensationSFD (Start Frame Delimiter)length of the payloadHEC (Header Error Check) protection of signal, service and length, x16 x12 x5 112816synchronizationSFDPLCP preamble881616signal service length HECvariablebitspayloadPLCP header802.11 - MAC layer I - DFWMAC Traffic services Asynchronous Data Service (mandatory) exchange of data packets based on “best-effort” support of broadcast and multicast Time-Bounded Service (optional) implemented using PCF (Point Coordination Function) Access methods 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) Distributed Foundation Wireless MAC avoids hidden terminal problem DFWMAC- PCF (optional) access point polls terminals according to a list802.11 - MAC layer II 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 serviceDIFSDIFSmedium busyPIFSSIFSdirect access ifmedium is free DIFScontentionnext framet5
9/29/08802.11 - CSMA/CA access method I Station ready to send starts sensing the medium (Carrier Sensebased 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, thenthe station must additionally wait a random back-off time (collisionavoidance, multiple of slot-time) If another station occupies the medium during the back-off time ofthe station, the back-off timer stops (fairness)DIFScontention window(randomized back-offmechanism)DIFSmedium busynext frametdirect access ifmedium is free DIFSslot time (20µs)802.11 - competing stations - simple versionDIFSDIFSDIFSboe borstation1DIFSboe borboebusyboe busyboeborboe busyboeborboe busystation2busystation3station4boe borstation5tbusymedium not idle (frame, ack etc.)boe elapsed backoff timepacket arrival at MACbor residual backoff time802.11 - CSMA/CA access method II Sending unicast packets station has to wait for DIFS before sending data receivers acknowledge at once (after waiting for SIFS) if the packetwas received correctly (CRC) automatic retransmission of data packets in case of Sotherstationswaiting timedatatcontention6
9/29/08802.11 - DFWMAC Sending unicast packets 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 ACKother stations store medium reservations distributed via RTS and CTSDIFSsenderRTSdataSIFSreceiverSIFSCTS SIFSACKDIFSNAV (RTS)otherstationsdataNAV (CTS)tdefer Sreceiverfrag2SIFSCTSSIFSSIFSACK1SIFSACK2NAV (RTS)NAV (CTS)NAV (frag1)otherstationsDIFSNAV (ACK1)contentiondatatDFWMAC-PCF I (almost never used)t0 t1medium busy stationsstations‘NAVSuperFrameU2NAV7
9/29/08DFWMAC-PCF elessstationsNAVstations‘NAVcontention free periodcontentionperiodt802.11 - 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 (logical) Miscellaneous bytes2FrameControlbits2sending time, checksum, frame control, data2666260-2312Duration/ Address Address Address Sequence AddressDataID123Control4241ProtocolToType SubtypeversionDS11From MoreDS Frag1Retry1114CRC1Power MoreWEP OrderMgmt DataMAC address formatDS: Distribution SystemAP: Access PointDA: Destination AddressSA: Source AddressBSSID: Basic Service Set IdentifierRA: Receiver AddressTA: Transmitter Address8
9/29/08Special Frames: ACK, RTS, CTS Acknowledgementbytes2FrameControlACK Request To Sendbytes2FrameControlRTS Clear To on64ReceiverCRCAddress664Receiver TransmitterCRCAddress Address64ReceiverCRCAddress802.11 - MAC management Synchronization try to find a LAN, try to stay within a LAN synchronization of internal clocks, generation of beacons Power management sleep-mode without missing a message periodic sleep, frame buffering, traffic measurements Association/Reassociation integration into a LAN roaming, i.e., change networks by changing access points scanning, i.e., active search for a network MIB - Management Information Base managing, read, writeSynchronization using a Beacon(infrastructure)beacon interval(20ms – 1s)accesspointmediumBBbusybusyBbusyBbusytvalue of the timestampB beacon frame9
9/29/08Synchronization using a Beacon (ad-hoc)beacon busytB beacon framevalue of the timestamprandom delayPower 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 Infrastructure Traffic Indication Map (TIM) Delivery Traffic Indication Map (DTIM) list of unicast receivers transmitted by APlist of broadcast/multicast receivers transmitted by AP Ad-hoc Ad-hoc Traffic Indication Map (ATIM) announcement of receivers by stations buffering framesmore complicated - no central APcollision of ATIMs possible (scalability?) APSD (Automatic Power Save Delivery) new method in 802.11e replacing above schemesPower saving with wake-up patterns(infrastructure)TIM intervalaccesspointmediumDTIM intervalD BTbusybusyTdD BbusybusypstationdtT TIMD DTIMB broadcast/multicastawakep PS polld data transmissionto/from the station10
9/29/08Power saving with wake-up patterns (adhoc)ATIMwindowstation1beacon intervalB1AB2station2B beacon frameawakeB2DaB1dA transmit ATIMrandom delaya acknowledge ATIMtDtransmit datad acknowledge data802.11 - Roaming No or bad connection? Then perform: Scanning scan the environment, i.e., listen into the medium for beacon signalsor send probes into the medium and wait for an answer Reassociation Request station sends a request to one or several AP(s) Reassociation Response success: AP has answered, station can now participatefailure: continue scanning AP accepts Reassociation Request signal the new station to the distribution systemthe distribution system updates its data base (i.e., location information)typically, the distribution system now informs the old AP so it canrelease resources Fast roaming – 802.11r e.g., for vehicle-to-roadside networksWLAN: IEEE 802.11b Data rate 1, 2, 5.5, 11 Mbit/s, dependingon SNRUser data rate max. approx. 6Mbit/s Transmission range 300m outdoor, 30m indoorMax. data rate 10m indoor Frequency Connection set-up time Security Limited, WEP insecure, SSID Many products, many vendorsLimited (no automated keydistribution, sym. Encryption)Special Advantages/DisadvantagesDSSS, 2.4 GHz ISM-band AvailabilityTyp. Best effort, no guarantees(unless polling is used, limitedsupport in products)Manageability Connectionless/always onQuality of Service Advantage: many installedsystems, lot of experience,available worldwide, free ISM-band,many vendors, integrated inlaptops, simple systemDisadvantage: heavy interferenceon ISM-band, no serviceguarantees, slow relative speedonly11
9/29/08IEEE 802.11b – PHY frame formatsLong PLCP PPDU format12816synchronizationSFD881616signal service length HECPLCP preamblebitsvariablepayloadPLCP header192 µs at 1 Mbit/s DBPSK1, 2, 5.5 or 11 Mbit/sShort PLCP PPDU format (optional)56short synch.16SFD881616signal service length HECPLCP preamble(1 Mbit/s, DBPSK)bitsvariablepayloadPLCP header(2 Mbit/s, DQPSK)96 µs2, 5.5 or 11 Mbit/sChannel selection (non-overlapping)Europe (ETSI)channel 12400channel 7channel 1324422472241222 MHz2483.5[MHz]US (FCC)/Canada (IC)channel 12400channel 6channel 1124372462241222 MHz2483.5[MHz]WLAN: IEEE 802.11a Data rate 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s,depending on SNRUser throughput (1500 bytepackets): 5.3 (6), 18 (24), 24 (36),32 (54)6, 12, 24 Mbit/s mandatoryE.g., 54 Mbit/s up to 5 m, 48 up to12 m, 36 up to 25 m, 24 up to 30m,18 up to 40 m, 12 up to 60 m Limited, WEP insecure, SSIDTyp. best effort, no guarantees(same as all 802.11 products)ManageabilityLimited (no automated keydistribution, sym. Encryption)Special Advantages/Disadvantages Free 5.15-5.25, 5.25-5.35,5.725-5.825 GHz ISM-bandSecurity Connectionless/always onQuality of ServiceFrequency 100m outdoor, 10m indoor Connection set-up time Transmission range Advantage: fits into 802.xstandards, free ISM-band,available, simple system, uses lesscrowded 5 GHz bandDisadvantage: stronger shadingdue to higher frequency, no QoSAvailability Some products, some vendors12
9/29/08IEEE 802.11a – PHY frame format4rate1121616reserved length parity tailvariable6service payloadtailvariablebitspadPLCP headerPLCP preamblesignal12data1variable6 Mbit/ssymbols6, 9, 12, 18, 24, 36, 48, 54 Mbit/sOperating channels of 802.11a in Europe36515040444852566064channel5180 5200 5220 5240 5260 5280 5300 53205350 [MHz]16.6 MHz1005470104108140channel5500 5520 5540 5560 5580 5600 5620 5640 5660 5680 57005725[MHz]16.6 MHz112116120124128132136center frequency 5000 5*channel number [MHz]Operating channels for 802.11a / US U-NII365150404448525660645180 5200 5220 5240 5260 5280 5300 5320channel5350 [MHz]16.6 MHz149153157161channelcenter frequency 5000 5*channel number [MHz]5725 5745 5765 5785 5805 5825 [MHz]16.6 MHz13
9/29/08OFDM in IEEE 802.11a OFDM with 52 used subcarriers (64 in total) 48 data 4 pilot (plus 12 virtual subcarriers) 312.5 kHz spacing312.5 kHzpilot-26 -21-7 -1 1721 26channel center frequencysubcarriernumberWLAN: IEEE 802.11 – current developments(05/2008) 802.11c: Bridge Support Successful successor of 802.11b, performance loss during mixed operation with .11b802.11h: Spectrum Managed 802.11a Establish an Inter-Access Point Protocol for data exchange via the distribution system802.11g: Data Rates 20 Mbit/s at 2.4 GHz; 54 Mbit/s, OFDM Enhance the current 802.11 MAC to expand support for applications with Quality ofService requirements, and in the capabilities and efficiency of the protocolDefinition of a data flow (“connection”) with parameters like rate, burst, period supportedby HCCA (HCF (Hybrid Coordinator Function) Controlled Channel Access, optional)Additional energy saving mechanisms and more efficient retransmissionEDCA (Enhanced Distributed Channel Access): high priority traffic waits less for channelaccess802.11F: Inter-Access Point Protocol (withdrawn) Support of additional regulations related to channel selection, hopping sequences802.11e: MAC Enhancements – QoS Definition of MAC procedures to support bridges as extension to 802.1D802.11d: Regulatory Domain Update Extension for operation of 802.11a in Europe by mechanisms like channel measurementfor dynamic channel selection (DFS, Dynamic Frequency Selection) and power control(TPC, Transmit Power Control)802.11i: Enhanced Security Mechanisms Enhance the current 802.11 MAC to provide improvements in security.TKIP enhances the insecure WEP, but remains compatible to older WEP systemsAES provides a secure encryption method and is based on new hardwareWLAN: IEEE 802.11– current developments(05/2008) 802.11j: Extensions for operations in Japan Changes of PHY and MAC with the goal of 100Mbit/s at MAC SAPMIMO antennas (Multiple Input Multiple Output), up to 600Mbit/s are currently feasibleHowever, still a large overhead due to protocol headers and inefficient mechanisms802.11p: Inter car communications Devices and access points should be able to estimate channel quality in order to be ableto choose a better access point of channel802.11m: Updates of the 802.11-2007 standard802.11n: Higher data rates above 100Mbit/s Comprises amendments a, b, d, e, g, h, i, j802.11k: Methods for channel measurements Changes of 802.11a for operation at 5GHz in Japan using only half the channel width atlarger range802.11-2007: Current “complete” standard Communication between cars/road side and cars/carsPlanned for relative speeds of min. 200km/h and ranges over 1000mUsage of 5.850-5.925GHz band in North America802.11r: Faster Handover between BSS Secure, fast handover of a station from one AP to another within an ESSCurrent mechanisms (even newer standards like 802.11i) plus incompatible devices fromdifferent vendors are massive problems for the use of, e.g., VoIP in WLANsHandover should be feasible within 50ms in order to support multimedia applicationsefficiently14
9/29/08WLAN: IEEE 802.11– current developments(05/2008) 802.11s: Mesh Networking 802.11T: Performance evaluation of 802.11 networks Standardization of performance measurement schemes802.11u: Interworking with additional external networks802.11v: Network management Design of a self-configuring Wireless Distribution System (WDS) based on802.11Support of point-to-point and broadcast communication across several hopsExtensions of current management functions, channel measurementsDefinition of a unified interface802.11w: Securing of network control Classical standards like 802.11, but also 802.11i protect only data frames, notthe 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 USA802.11z: Extension to direct link setup Note: Not all “standards” will end in products, many ideas get stuck atworking group levelInfo: www.ieee802.org/11/, 802wirelessworld.com, standards.ieee.org/getieee802/ 15
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 802.11 LAN IBSS 2 802.11 LAN IBSS 1 STA 1 STA 4 STA 5 STA 2 STA 3 IEEE standard 802.11 mobile terminal access point fixed terminal
1 Spring, 2003 EE 4272 Chapter 13. Local Area Network Technology LAN Applications LAN Architecture ¾Protocol Architecture ¾Topologies ¾MAC Bus LANs Ring LANs Star LANs Extended LANs: Bridge Spring, 2003 EE 4272 LAN Applications Personal computerLANs ¾Low cost ¾Limited data rate Backend networks and storage area networks
information that are recommended to further a student's knowledge of wireless LANs: CWNA Study Guide. This book from Planet3 Wireless contains extensive information on the administration of wireless LANs, and prepares students to take the CWNA exam. The Internet provides many websi
A wireless Local Area Network (LAN) is a moderate to high-speed flexible data communications system implemented as an extension to, or as an alternative for, a wired Local Area Network. Using radio frequency (RF) technology, Wireless LANs transmit and receive data over the air, minimizing the need for wired connections. Thus, wireless LANs combine
ECB-3220 has high transmitted output power and high receivable sensitivity. High . The following list describes some of the many applications made possible through the power and flexibility of wireless LANs: a) Difficult-to-wire environments . Network managers implement wireless LANs to provide backup for
How Cisco Tracks RFID with Active RFID and Wireless LANs Active RFID tags and WLANs ensure compliance with corporate finance and government regulations. Cisco IT Case Study / Wireless / Cisco RFID Solutions: Maintaining accurate information about the location of valuable equipment is a
area like a department or a college campus. LANs are typically linked together by WANs. LANs tend to connect to WANs at only a few points, through expensive leased lines. LANs are optimized for speed over short distances. WANs are optimized for reliability over long distances. Because of all this, WA
The LAN itself is referred to as a broadcast domain, because if any device within the LAN sends out a broadcast packet, it will be transmitted to all devices in that LAN, but not to devices beyond the LAN. Using VLANs to segment LANs As LANs became larger, data rates became fa ster, and users desired greater flexibility, the
LANs, High Speed LANs & LAN Interconnections, 2002, Dr. Z. Sun 8 IEEE 802 relevant to LANs „ 802.1 — High layer LAN Protocol: Overview & architecture, bridging, VLAN „ 802.2 — Logical Link Control services Working Group (WG) (inactive) „ 802.3 — Ethernet (CSMA/CD) WG: access method & physical signalling „ 802.4 — Token Bus WG: access method & physical signalling (inactive)
