Chapter 3: Overview 802 Standard
IEEE - Institute of Electrical and Electronics Engineers What is the IEEE? international non-profit, professional organization for the advancement of technology related to electricity. largest technical professional organization in the world (in number of members), with more than 360,000 members in around 175 countries (2005) What does the IEEE do? produces 30 percent of the world's literature in the electrical and electronics engineering and computer science field, sponsors or cosponsors more than 300 international technical conferences each year. publishes an extensive range of peer-reviewed journals, major international standards body (nearly 900 active standards with 700 under development). - 2 -
Notable IEEE Committees and Formats IEEE 754 floating point arithmetic specifications IEEE 802 LAN/MAN IEEE 802.11 Wireless Networking IEEE 829 Software Test Documentation IEEE 896 Futurebus IEEE 1003 POSIX IEEE 1076 VHDL VHSIC Hardware Description Language IEEE 1149.1 JTAG IEEE 1275 Open Firmware IEEE 1284 Parallel port IEEE P1363 Public key cryptography IEEE 1394 Serial Bus ("FireWire") IEEE 12207 Information Technology - 3 -
family of IEEE standards on metropolitan area networks local area networks personal area networks IEEE 802 restricted to non-isochrononous networks carrying variable-size packets. By contrast: in cell-based networks data is transmitted in short, uniformly sized units called cells. Isochronous networks, where data is transmitted as a steady stream of octets, or groups of octets, at regular time intervals (example: mobile phone networks) From Wikipedia - 4 -
IEEE 802 Overview IEEE 802.1 Higher layer LAN protocols IEEE 802.2 Logical link control IEEE 802.3 Ethernet IEEE 802.4 Token bus (disbanded) IEEE 802.5 Token Ring IEEE 802.6 Metropolitan Area Networks (disbanded) IEEE 802.7 Broadband TAG (disbanded) IEEE 802.8 Fiber Optic TAG (disbanded) IEEE 802.9 Integrated Services LAN (disbanded) IEEE 802.10 Interoperable LAN Security (disbanded) IEEE 802.11 Wireless LAN IEEE 802.12 demand priority IEEE 802.13 (not used) IEEE 802.14 Cable modems (disbanded) IEEE 802.15 Wireless PAN IEEE 802.16 Broadband wireless access IEEE 802.17 Resilient packet ring IEEE 802.18 Radio Regulatory TAG IEEE 802.19 Coexistence TAG IEEE 802.20 Mobile Broadband Wireless Access IEEE 802.21 Media Independent Handoff IEEE 802.22 Wireless Regional Area Networks IEEE 802.23 Emergency Services www.ieee.org, Tanenbaum S.95-5 -
Network Differentiation by Range Body Area Networks (BAN) Personal Area Network (PAN) wireless PAN (IEEE 802.15) 802.15.1/Bluetooth 802.15.3/UWB 802.15.4/ZigBee Local Area Network (LAN) wireless LAN (IEEE 802.11) HomePNA Power line communication (HomePlug) Metropolitan Area Network (MAN) IEEE 802.16/WiMAX Mobile Broadband Wireless Access IEEE 802.20 Wireless Regional Area Network IEEE 802.22-6 -
OSI Layers and IEEE 802 Services and protocols specified in IEEE 802 address the lower two layers (Data Link and Physical) of the seven-layer OSI networking reference model 802.11 { 802.15 802.16 802.20-7 -
Chapter 4: Wireless LANs IEEE 802.11 These slides are to a great extent based on slides of Jochen Schiller, Mobilkommunikation, Chapter7
Overview Chapter 4 4.1 Characteristics of WLANs 4.2 Overview on IEEE 802.11 4.3 IEEE 802.11 Physical Layer Legacy 802.11, 802.11b, a, g, n Future developments: 802.11ac,ad 4.4 IEEE 802.11 MAC Layer 4.5 Security in 802.11-9 -
4.1 Characteristics and Design Goals
Characteristics of wireless LANs Advantages very flexible within the reception area 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... Disadvantages typically lower data rate compared to wired networks (600 Mbit/s vs. 10 Gbit/s), higher error rates (10-4 instead of 10-12 ) many proprietary solutions, especially for higher bit-rates, standards take time (e.g. 802.11n) products have to follow many national restrictions if working wireless, it takes a very long time to establish global solutions like, e.g., IMT-2000 heavy interference on ISM band, no service guarantees - 11 -
Design goals for wireless LANs global, seamless operation low power for battery use no special permissions or licenses needed to use the WLAN 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 - 12 -
4.2 Overview on IEEE 802.11
The IEEE 802.11 Standard 802.11 Working Group for Wireless LANs over-the-air interface between wireless client and base station among wireless clients comparable to the IEEE 802.3 standard for Ethernet for wired LANs addresses both the Physical (PHY) and Media Access Control (MAC) layers resolve compatibility issues between manufacturers of Wireless LAN equipment. [http://standards.ieee.org/wireless/overview.html] - 14 -
Infrastructure vs. Ad-hoc Networks infrastructure network AP AP wired network AP: Access Point AP ad-hoc network - 15 -
802.11 - Architecture of an infrastructure network Station (STA) STA 1 ESS 802.11 LAN BSS 1 Access Point Distribution System BSS 2 Access Point 802.x LAN Portal terminal with access mechanisms to the wireless medium and radio contact to the access point Basic Service Set (BSS) group of stations (incl. AP) 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 STA 2 802.11 LAN STA 3-16 -
802.11 - Architecture of an ad-hoc network 802.11 LAN Direct communication within a limited range STA 1 IBSS 1 STA 3 Station (STA): terminal with access mechanisms to the wireless medium STA 2 Independent Basic Service Set (IBSS): group of stations using the same radio frequency IBSS 2 STA 5 STA 4 802.11 LAN - 17 -
Legacy IEEE 802.11 Original version released in 1997 1 and 2 Mbit/s via infrared (IR) and ISM band (2.4 Ghz) IR was never implemented in commercial products Media access method: Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) 5 different, somewhat-interoperable, commercial products appeared using the original specification, e.g. Alvarion PRO.11 and BreezeAccess-II), Netwave Technologies (AirSurfer Plus and AirSurfer Pro) and Proxim (OpenAir). Weakness of original spec.: too many choices, interoperability = challenge rapidly supplemented by 802.11b. - 18 -
IEEE 802.11b/a IEEE 802.11 b Higher Speed Physical Layer Extension in the 2.4 GHz Band (1999) 2 additional modulation schemes: CCK, PBCC 5.5 or 11 Mbit/s Uses DSSS, downward compatible to 802.11 1 Mbit/s IEEE 802.11 a High Speed Physical Layer in the 5 GHz Band, (1999) OFDM with BPSK, QPSK, 16-QAM and 64-QAM, coding rates 1/2, 3/4 leading to data rates of 6 54 Mbit/s - 19 -
IEEE 802.11g/n IEEE 802.11 g Further Higher Data Rate Extension for the 2.4 GHz Band (2003) OFDM within 2.4 GHz band Data rates up to 54 Mbit/s as in 802.11a Downwards compatible to 802.11 IEEE 802.11 n Enhancements for Higher Throughput (2009) Multiple Input Multiple Output, Frame Aggregation Gross data rates up to 600 Mbit/s - 20 -
IEEE 802.11 c-r IEEE 802.11c (included in 802.1D) (2001) Bridging functionaliy for data exchange between wireless and wired networks (MAC layer) IEEE 802.11d (2001) Specification for operation in additional regulatory domains IEEE 802.11e (2005) Quality-of-Service support (ongoing work) Different service classes, traffic types IEEE 802.11F (withdrawn 2006) Specification of an Inter-Access Point Protocol (IAPP) Seamless handover on link-layer; support of different vendors in larger WLANs IEEE 802.11h (2004) Spectrum Management in Europe for 5 GHz band (802.11a) Dynamic Frequency Selection/Transmit Power Control IEEE 802.11i (2004) Enhancing Security and Authentication Extension of basic WEP (Wired Equivalent Privacy) IEEE 802.11j (2004) 4.9-5 GHz adaptation for Japan IEEE 802.11k (2008) Enhancements for Radio Resource Measurements IEEE 802.11p (2010) For vehicular usage, speeds up to 200km/h 1 km range, 5 GHz frequency band WAVE Wireless Access for the Vehicular Environment IEEE 802.11r (2008) Improves L2 handover, Fast Roaming - 21 -
IEEE 802.11 s-ai IEEE 802.11s (2011) Def. of Wireless Distribution Systems and Extended Service Set Mesh Networking Define self configuring multi-hop topologies to improve ad-hoc capabilities of 802.11 IEEE 802.11T Wireless Performance Prediction (WPP) - test methods and metrics IEEE 802.11u (2011) Interworking with non-802.11 networks IEEE 802.11v (2011) Wireless Network Management IEEE 802.11w (2009) Protected Management Frames IEEE 802.11y (2008) 3650-3700 MHz operation in the U.S. IEEE 802.11z (2010) Extensions to Direct Link Setup (DLS) IEEE 802.11aa (2012) robust streaming of audio video transport streams IEEE 802.11ac: (ongoing) very high throughput < 6 GHz IEEE 802.11ad: (ongoing) Very high throughput at 60 GHz IEEE 802.11ae: (2012) QoS Management IEEE 802.11af: (ongoing) WLAN in TV Whitespace IEEE 802.11ah: (ongoing) Sub 1 GHz IEEE 802.11ai: (ongoing) Fast Initial Link Setup IEEE 802.11.2 Def. of Performance metrics, measurement methodologies and test conditions IEEE 802.11 a, b, d, e, g, h, i,j now included in updated standard IEEE 802.11-2007 - 22 -
IEEE Standard 802.11 mobile terminal fixed terminal application TCP IP LLC access point LLC infrastructure network application TCP IP 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 - 23 -
802.11 - Layers and functions PHY DLC MAC access mechanisms, fragmentation, encryption MAC Management synchronization, roaming, MIB, power management LLC MAC PLCP PMD MAC Management PHY Management Station Management PLCP (Physical Layer Convergence Protocol) clear channel assessment signal (carrier sense) PMD (Physical Medium Dependent) modulation, coding PHY Management channel selection, MIB Station Management coordination of all management functions - 24 -
4.3 IEEE 802.11 Physical Layer 4.3.1 IEEE 802.11 4.3.2 IEEE 802.11b 4.3.3 IEEE 802.11a 4.3.4 IEEE 802.11g 4.3.5 IEEE 802.11n
4.3.1. IEEE 802.11 FHSS (Frequency Hopping Spread Spectrum) spreading, despreading, signal strength, typ. 1 Mbit/s min. 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/s max. radiated power 1 W (USA), 100 mw (EU), min. 1mW Infrared 850-950 nm, diffuse light, typ. 10 m range carrier detection, energy detection, synchonization DSSS was most commonly used in the market - 26 -
Recap from Chapter 2: DSSS XOR of the signal with pseudo-random number (chipping sequence) many chips per bit (e.g., 128) result in higher bandwidth of the signal Advantages reduces frequency selective t b fading in cellular networks 0 1 base stations can use the same frequency range several base stations can detect and recover the signal soft handover Disadvantages precise power control necessary t c 0 1 1 0 1 0 1 0 1 1 0 1 0 1 0 1 1 0 1 0 1 1 0 0 1 0 1 0 t b : bit period t c : chip period user data XOR chipping sequence = resulting signal - 27 -
DSSS Similar to CDMA, but only one Spreading Sequence used for all users not possible for several users to operate in same frequency at same time Spreading to increase robustness 11-chip Barker Code (+1, 1, +1, +1, 1, +1, +1, +1, 1, 1, 1) US 11 Channels, EU 13 channels are available; 5 MHz apart from each other, each 22 MHz wide co-channel interference DBPSK modulation for 1 Mbit/s (Differential Binary Phase Shift Keying), DQPSK for 2 Mbit/s (Differential Quadrature PSK) Scrambling with s(z)=z 7 +z 4 +1, to eliminate DC components preamble and header of a frame is always transmitted with 1 Mbit/s, rest of transmission 1 or 2 Mbit/s max. radiated power 1 W (USA), 100 mw (EU), min. 1mW - 28 -
Physical Layer DSSS (Direct Sequence Spread Spectrum) transmit 1 Mbit/s 1 User data 0 0 1 Symbols, comprising of chips receive 00110011011 11 0 01100100 11001100100 00110011011 DBPSK 2 Mbit/s 1 0 0 1 0 0 1 1 transmit 00110011011 11 0 01100100 11001100100 00110011011 11001100100 00 1 10011011 11001100100 00110011011 receive DQPSK - 29 -
DSSS PHY packet format Synchronization synch., gain setting, energy detection, frequency offset compensation SFD (Start Frame Delimiter) 1111001110100000 Signal data rate of the payload coded in steps of 100 kbit/s; 0A: 1 Mbit/s DBPSK; 14: 2 Mbit/s DQPSK Service Length future use, 00: 802.11 compliant of the payload HEC (Header Error Check) protection of signal, service and length, x 16 +x 12 +x 5 +1 128 16 8 8 16 16 variable bits synchronization SFD signal service length HEC payload PLCP preamble PLCP header - 30 -
4.3.2 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 Free 2.4 GHz ISM band Only compatible to DSSS of legacy 802.11, not to FHSS Meanwhile superseded by faster standard extensions However downward compatibility still provided - 31 -
802.11b PHY: Modulation Schemes DBPSK (1 Mbit/s) DQPSK (2 Mbit/s) Complementary Coded Keying (CCK) Complex spreading codes Chip Rate 11 Mchip/s Symbol: sequence of 4 chips (5.5 Mbit/s) or 8 chips (11 Mbit/s) 5.5 Mbit/s: 4 bits per symbol, 2 chips per bit 11 Mbit/s: 8 bits per symbol, 1 chip per bit Low-level modulation scheme: DQSK - 32 -
Physical Layer: 5.5 Mbit/s CCK (Complementary Coded Keying) 2 bit 2 bit 1 0 1 0 1 1 0 1 user data byte A1 B1 A2 B2 A value 0 1 j -1 -j 1-1 j -j 1 j 1-1 j 1 j -1 -j 2 -j 1 j -1 j -j -1 1 3 1-1 j -j 1 j -1 -j complementary sequences 1 j -j B times -1 phase rotation of CCK symbol j -1 -j 1 -j j 1-1 QPSK - 33 -
Physical Layer: 11 Mbit/s 6 bit 2 bit 0 1 1 0 1 0 1 0 CCK (Complementary Coded Keying) User data byte A B A value 0 1 j -1 -j 1-1 j -j 1 j 1-1 j 1 j -1 -j 2 -j 1 j -1 j -j -1 1 22 63 1-1 j -j 1 j -1 -j -1 j 1 -j j -j -1 1 1 j -j B times -1 phase rotation of CCK symbol j -1 j 1 -j j 1-1 QPSK complementary sequences - 34 -
PHY Transmission Modes: Overview Bit rate Mbit/s Modulation scheme Chips/ bit Chip rate Mchips/s Symbol Rate MSyms /s Bits/ Symbol RF BW MHz 1 DBPSK 11 real 11 1 1 22 2 DQPSK 5.5 complex 11 1 2 22 5.5 CCK 2 complex 11 1.375 4 22 sensitivity against interference 11 CCK 1 complex 11 1.375 8 22 Transmit power: min. 1 mw; max. 100 mw EIRP (Europe); 1000mW (US); 200 mw (Japan) - 35 -
Channel selection (non-overlapping) Europe (ETSI) channel 1 channel 7 channel 13 2400 2412 2442 2472 2483.5 22 MHz MHz US (FCC)/Canada (IC) channel 1 channel 6 channel 11 2400 2412 2437 2462 2483.5 22 MHz MHz - 36 -
Spectrum of DSSS signal http://www-sop.inria.fr/intech/reseau_ss_fil_presentations/aad.pdf - 37 -
IEEE 802.11b PHY frame formats Long PLCP PPDU format 128 16 8 8 16 16 variable bits synchronization SFD signal servicelength HEC payload PLCP preamble PLCP header 192 µs at 1 Mbit/s DBPSK 1, 2, 5.5 or 11 Mbit/s Short PLCP PPDU format (optional) 56 16 8 8 16 16 variable bits short synch. SFD signal servicelength HEC payload PLCP preamble (1 Mbit/s, DBPSK) PLCP header (2 Mbit/s, DQPSK) 96 µs 2, 5.5 or 11 Mbit/s - 38 -
802.11b PHY Frame Format Long Frame: Mandatory Frame Format, backwards compatible to 802.11 Optional Short Frame half the length of Long Frame and further differences: Short sync field: scrambled 0s instead of scrambled 1s SFD of short is mirrored SFD of long frame Receiver not able to decode short frames can only detect activity on channel - 39 -