Chapter 3: Overview 802 Standard

Transcription

1 Chapter 3: Overview 802 Standard

2 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)

3 Notable IEEE Committees and Formats IEEE 754 floating point arithmetic specifications IEEE 802 LAN/MAN IEEE Wireless Networking IEEE 829 Software Test Documentation IEEE 896 Futurebus IEEE 1003 POSIX IEEE 1076 VHDL VHSIC Hardware Description Language IEEE JTAG IEEE 1275 Open Firmware IEEE 1284 Parallel port IEEE P1363 Public key cryptography IEEE 1394 Serial Bus ("FireWire") IEEE Information Technology - 3 -

4 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 -

5 IEEE 802 Overview IEEE Higher layer LAN protocols IEEE Logical link control IEEE Ethernet IEEE Token bus (disbanded) IEEE Token Ring IEEE Metropolitan Area Networks (disbanded) IEEE Broadband TAG (disbanded) IEEE Fiber Optic TAG (disbanded) IEEE Integrated Services LAN (disbanded) IEEE Interoperable LAN Security (disbanded) IEEE Wireless LAN IEEE demand priority IEEE (not used) IEEE Cable modems (disbanded) IEEE Wireless PAN IEEE Broadband wireless access IEEE Resilient packet ring IEEE Radio Regulatory TAG IEEE Coexistence TAG IEEE Mobile Broadband Wireless Access IEEE Media Independent Handoff IEEE Wireless Regional Area Networks IEEE Emergency Services Tanenbaum S

6 Network Differentiation by Range Body Area Networks (BAN) Personal Area Network (PAN) wireless PAN (IEEE ) /Bluetooth /UWB /ZigBee Local Area Network (LAN) wireless LAN (IEEE ) HomePNA Power line communication (HomePlug) Metropolitan Area Network (MAN) IEEE /WiMAX Mobile Broadband Wireless Access IEEE Wireless Regional Area Network IEEE

7 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 {

8 Chapter 4: Wireless LANs IEEE These slides are to a great extent based on slides of Jochen Schiller, Mobilkommunikation, Chapter7

9 Overview Chapter Characteristics of WLANs 4.2 Overview on IEEE IEEE Physical Layer Legacy , b, a, g, n Future developments: ac,ad 4.4 IEEE MAC Layer 4.5 Security in

10 4.1 Characteristics and Design Goals

11 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 ) many proprietary solutions, especially for higher bit-rates, standards take time (e.g n) 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

12 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

13 4.2 Overview on IEEE

14 The IEEE Standard Working Group for Wireless LANs over-the-air interface between wireless client and base station among wireless clients comparable to the IEEE 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. [

15 Infrastructure vs. Ad-hoc Networks infrastructure network AP AP wired network AP: Access Point AP ad-hoc network

16 Architecture of an infrastructure network Station (STA) STA 1 ESS 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 LAN STA

17 Architecture of an ad-hoc network 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 LAN

18 Legacy IEEE Original version released in 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 b

19 IEEE b/a IEEE 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 Mbit/s IEEE 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

20 IEEE g/n IEEE 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 a Downwards compatible to IEEE n Enhancements for Higher Throughput (2009) Multiple Input Multiple Output, Frame Aggregation Gross data rates up to 600 Mbit/s

21 IEEE c-r IEEE c (included in 802.1D) (2001) Bridging functionaliy for data exchange between wireless and wired networks (MAC layer) IEEE d (2001) Specification for operation in additional regulatory domains IEEE e (2005) Quality-of-Service support (ongoing work) Different service classes, traffic types IEEE F (withdrawn 2006) Specification of an Inter-Access Point Protocol (IAPP) Seamless handover on link-layer; support of different vendors in larger WLANs IEEE h (2004) Spectrum Management in Europe for 5 GHz band (802.11a) Dynamic Frequency Selection/Transmit Power Control IEEE i (2004) Enhancing Security and Authentication Extension of basic WEP (Wired Equivalent Privacy) IEEE j (2004) GHz adaptation for Japan IEEE k (2008) Enhancements for Radio Resource Measurements IEEE p (2010) For vehicular usage, speeds up to 200km/h 1 km range, 5 GHz frequency band WAVE Wireless Access for the Vehicular Environment IEEE r (2008) Improves L2 handover, Fast Roaming

22 IEEE s-ai IEEE s (2011) Def. of Wireless Distribution Systems and Extended Service Set Mesh Networking Define self configuring multi-hop topologies to improve ad-hoc capabilities of IEEE T Wireless Performance Prediction (WPP) - test methods and metrics IEEE u (2011) Interworking with non networks IEEE v (2011) Wireless Network Management IEEE w (2009) Protected Management Frames IEEE y (2008) MHz operation in the U.S. IEEE z (2010) Extensions to Direct Link Setup (DLS) IEEE aa (2012) robust streaming of audio video transport streams IEEE ac: (ongoing) very high throughput < 6 GHz IEEE ad: (ongoing) Very high throughput at 60 GHz IEEE ae: (2012) QoS Management IEEE af: (ongoing) WLAN in TV Whitespace IEEE ah: (ongoing) Sub 1 GHz IEEE ai: (ongoing) Fast Initial Link Setup IEEE Def. of Performance metrics, measurement methodologies and test conditions IEEE a, b, d, e, g, h, i,j now included in updated standard IEEE

23 IEEE Standard mobile terminal fixed terminal application TCP IP LLC access point LLC infrastructure network application TCP IP LLC MAC MAC MAC MAC PHY PHY PHY PHY

24 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

25 4.3 IEEE Physical Layer IEEE IEEE b IEEE a IEEE g IEEE n

26 IEEE 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 nm, diffuse light, typ. 10 m range carrier detection, energy detection, synchonization DSSS was most commonly used in the market

27 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 t b : bit period t c : chip period user data XOR chipping sequence = resulting signal

28 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

29 Physical Layer DSSS (Direct Sequence Spread Spectrum) transmit 1 Mbit/s 1 User data Symbols, comprising of chips receive DBPSK 2 Mbit/s transmit receive DQPSK

30 DSSS PHY packet format Synchronization synch., gain setting, energy detection, frequency offset compensation SFD (Start Frame Delimiter) 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: compliant of the payload HEC (Header Error Check) protection of signal, service and length, x 16 +x 12 +x variable bits synchronization SFD signal service length HEC payload PLCP preamble PLCP header

31 4.3.2 IEEE b 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 , not to FHSS Meanwhile superseded by faster standard extensions However downward compatibility still provided

32 802.11b 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

33 Physical Layer: 5.5 Mbit/s CCK (Complementary Coded Keying) 2 bit 2 bit 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 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

34 Physical Layer: 11 Mbit/s 6 bit 2 bit 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 j -j 1 j -1 -j -1 j 1 -j j -j j -j B times -1 phase rotation of CCK symbol j -1 j 1 -j j 1-1 QPSK complementary sequences

35 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 DQPSK 5.5 complex CCK 2 complex sensitivity against interference 11 CCK 1 complex Transmit power: min. 1 mw; max. 100 mw EIRP (Europe); 1000mW (US); 200 mw (Japan)

36 Channel selection (non-overlapping) Europe (ETSI) channel 1 channel 7 channel MHz MHz US (FCC)/Canada (IC) channel 1 channel 6 channel MHz MHz

37 Spectrum of DSSS signal

38 IEEE b PHY frame formats Long PLCP PPDU format 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) 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

39 802.11b PHY Frame Format Long Frame: Mandatory Frame Format, backwards compatible to 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