Wireless Local Area Network. Internet Protocol Suite

Transcription

1 Wireless Local Area Network Internet Protocol Suite Application layer File transfer protocol Telnet Hypertext transfer protocol Transport layer Network layer Host-tonetwork layer User datagram protocol Transmission control protocol Internet protocol IEEE Ethernet Data link layer Physical layer Logical link Medium Access 1

2 IEEE 802 LAN Family IEEE Institute of Electrical and Electronic Engineering Layers IEEE LLC Logical link IEEE Ethernet IEEE Token bus IEEE Token ring IEEE Wireless Medium access Physical IEEE WLAN IEEE Standard for Wireless LAN Medium Access (MAC) and Physical Layer (PHY) Specifications (1997) FHSS 2.4 GHz 1-2 Mbps DSSS 2.4 GHz 1-2 Mbps MAC IR 1-2 Mbps OFDM 5 GHz 6-54 Mbps (802.11a) DSSS/HR 2.4 GHz 1-11 Mbps (802.11b) 2

3 Network Topology (a) Independent Basic Service Set (IBSS) Ad hoc or peer-to-peer network (b) Infrastructure Basic Service Set (BSS) Access Point (i.e. Base Station) (a) (b) MT MT MT MT AP MT MT MT MT Physical layers in The original PHY layers FHSS DSSS IR Extensions IEEE a OFDM IEEE b HR/DSSS 3

4 IEEE PHY DSSS Direct Sequence Spread Spectrum ISM-band 2.45 GHz 1 Mbps uses DBPSK (Differential Binary Phase Shift Keying) 2 Mbps uses DQPSK (Differential Quadrature Phase Shift Keying) Spreading sequence: Barker word 11-bit Barker = {+1,-1,+1,+1,-1,+1,+1,+1,-1,-1,-1} Transmitted power 10 mw (Japan), 100 mw (Europe), 1000 mw (USA) IEEE PHY FHSS Frequency Hopping Spread Spectrum ISM-band 2.45 GHz 1 Mbps uses GFSK (Gaussian Frequency Shift Keying) M = 2 2 Mbps uses GFSK (Gaussian Frequency Shift Keying) M = 4 79 frequency channels (Europe and US) and 23 frequency channels (Japan) 1 MHz channels Minimum 2.5 hops/second The same transmitting power as DSSS 4

5 IEEE PHY Infrared Near-visible light as the transmission media Relies on light energy, reflected off objects or line of sight 1 Mbps uses 16-PPM (Pulse Position Modulation) 2 Mbps uses 4-PPM IEEE b PHY HR/DSSS ISM-band 2.45 GHz MSps = Mega Symbols per Second, CCK = Complementary Code Keying Data Rate Code Length Modulation Symbol Rate Bits/Symbol 1 Mbps 11 (Barker) DBPSK 1MSps 1 2 Mbps 11 (Barker) DQPSK 1MSps Mbps 8 (CCK) DQPSK MSps 4 11 Mbps 8 (CCK) DQPSK MSps 8 5

6 IEEE a OFDM Orthogonal Frequency Division Multiplexing (also used by HiperLAN/2) Transfer rates 6, 9, 12, 18, 24, 36, 48 and 54 Mbps Multi-carrier technique 1960 s Used both in wireless and wired systems Wired systems Discrete Multi-Tone OFDM How it works Divide available frequency spectrum into narrower sub-carriers Transmitting simultaneously over a number of subcarriers IEEE a uses 52 channels for each transmission (48 data sub carriers and 4 pilot sub carriers) 6

7 OFDM How it works cont OFDM uses an over-lapping modulation technique (b) not usually used in multicarrier (a) systems Saving bandwidth (a) (b) Ch Ch. 5 Frequency Frequency Saving of bandwidth Different Transfer Rates in OFDM Transfer rates 6 Mbps 9 Mbps 12 Mbps 18 Mbps 24 Mbps 36 Mbps 48 Mbps 54 Mbps Modulation BPSK BPSK QPSK QPSK 16-QAM 16-QAM 64-QAM 64-QAM Coding rate 1/2 3/4 1/2 3/4 1/2 3/4 2/3 3/4 7

8 IEEE Medium Access Control All the five physical layers described earlier use the same Medium Access Control Layer Two different modes of gaining access Distributed Coordination Function (DCF) Point Coordination Function (PCF) Only in infrastructure BSS (i.e. network with AP) Priority-based access Time deterministic by using a polling scheme IEEE MAC Responsibilities Controlling access to medium Reliable data delivery Fragmentation of frames ( byte) Roaming and authentication Power save functionality Control functions Addressing, frame check generation etc 8

9 IEEE MAC DCF Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) Physical and virtual carrier sense (NAV) is used when a node wants to transmit Contention-based access Not time deterministic Acknowledgement used for every frame Backoff is used if medium is busy or frame is lost Medium reservation with RTS/CTS MAC Frame format Management, control and data frames Byte Frame Duration control ID Address Sequen Address field ce control field MAC Header Frame body FCS MAC Trail Duration ID = NAV (Virtual Carrier Sense) FCS = Frame Check Sequence (32-bit Cyclic Redundancy Check) 9

10 Timing in Packet Transmission SIFS = Short InterFrame Space DIFS = Distributed IFS PIFS = Priority IFS SIFS, DIFS, PIFS and Slot time PHY dependent Packet Transmission 10

11 Fragmented Packet Transmission Hidden node problem Coverage area cell Coverage area MT 1 MT 1 AP MT 2 Coverage area MT 2 RTS/CTS clears the cell 11

12 Packet Transmission with RTS/CTS Backoff/Defer Access When medium sensed busy or a packet/frame loss Backoff time based on the slot time Draw an integer from a uniform distribution between 0 and CW (Contention Window) The CW also PHY dependant Multiply the randomised number with the slot time Backoff time 12

13 Packet Transmission with Backoff Times Link adaptation Not specified in the IEEE standard Uses signal strength/error rates on previous packet/frame transmissions a has eight rates Every rate has limited operating range Cell size fluctuates with the rate (lower rates have more robust coding schemes) Link adaptation is also called Dynamic Rate Shifting 13

14 MAC Management Synchronization In Infrastructured mode, MT synchronized with AP In ad hoc mode, MT synchronized with each other Power Management Wireless terminals have limited battery capacity Power safe features necessary Roaming MTs may enter a new BSS MTs must change AP (roam between cells) Handover in GSM Synchronization All STA in an infrastructure BSS are synchronized The AP maintains a clock The AP transmits periodic frames called Beacons containing a clock value Time between two beacons are called Beacons interval All STAs hearing the beacon updates their clock accordingly This prevents clock drifting The Beacon is transmitted using normal CSMA/CA Beacons may be delayed significantly 14

15 Synchronization cont Beacon interval Access Point B B B B Channel Time Stamp B Beacon Busy Time Power Management A MT may enter sleeping mode and turn of radio The AP maintains a list of MTs sleeping Packets destined for a MT are buffered at AP, these are sent when MT wakes up MT must wake up periodically to receive Beacons Beacons tell sleeping stations that they have buffered data MTs are required to stay awake for receiving buffered data 15

16 Alphabet soup in IEEE (1997) Three different PHY layers (DSSS, FHSS, IR) 2.45 GHz MAClayer a (1999) PHY layer (OFDM) 5 GHz b (1999) PHY layer (HR/DSSS) 2.45 GHz Alphabet soup in IEEE cont d (ongoing) Supplement to the MAC layer For supporting different output powers in different countries e (ongoing) Supplement to the MAC layer For providing QoS for time-sensitive traffic f (ongoing) Supplement to the MAC layer For achieving interoperability between different vendors 16

17 Alphabet soup in IEEE cont g (ongoing) PHY standard 2.4 GHz and 5 GHz (dual band) h (ongoing) Supplement to the MAC layer For complying with the European regulations for 5 GHz Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) i (ongoing) Supplement to the MAC layer For increasing the security in the standard Cell size vs. Transfer rate 17

18 Range vs. Transfer rate Bluetooth 18

19 Introduction Universal short-range wireless capability Uses 2.4-GHz band Gaussian Frequency Shift Keying (GFSK) Available globally for unlicensed users Raw bit rate 1 Mbps Up to 720 kbps of information carrying capacity Supports open-ended list of applications Data, audio, graphics, video Introduction Data and voice access points Real-time voice and data transmissions Cable replacement Eliminates need for numerous cable attachments for connection Ad hoc networking Device with Bluetooth radio can establish connection with another when in range 19

20 Introduction Bluetooth is a layered protocol architecture Core protocols Cable replacement and telephony control protocols Adopted protocols Core protocols Radio Baseband Link manager protocol (LMP) Logical link control and adaptation protocol (L2CAP) Service discovery protocol (SDP) Introduction Cable replacement protocol RFCOMM Telephony control protocol Telephony control specification binary (TCS BIN) Adopted protocols PPP TCP/UDP/IP OBEX WAE/WAP 20

21 Introduction Network configurations Piconet Piconet Basic unit of Bluetooth networking Master and one to seven slave devices Master determines channel and phase slave 1 slave 3 master slave 2 21

22 Network configurations Scatternet slave 1 slave 3 master slave 4 master slave 5 slave 2 Inter-Piconet Jumping X Y SLAVE Ay SLAVE By SLAVE Ax MASTER X SLAVE Cxy native MASTER Y offset y SLAVE Bx offset x SLAVE Dy 22

23 Robust Operation Frequency hopping High interference protection 1600 hops/s 79 (or 23) channels 1 MHz spacing 220 µs switching time Fast acknowledge FEC CVSD voice Radio Classes Classes of transmitters Class 1: Outputs 100 mw (20dBm) Power control mandatory Provides greatest distance Class 2: Outputs 2.4 mw (4dBm) Power control optional Class 3: Output is 1 mw (0dBm) Lowest power 23

24 Addressing Bluetooth Device Address (BD_ADDR) 48-bit IEEE 802 address 24-bit lower address part (LAP) 8-bit upper address part (UAP) Active Member Address (AM_ADDR) 3-bit active slave address all-zero broadcast address Parked Member Address (PM_ADDR) 8-bit parked slave address Frequency Hopping Sequence Master BD_ADDR sequence Master CLOCK phase slave 1 slave 2 master slave 3 slave 4 24

25 Hop Selection Mechanism HOP SELECTION NATIVE CLK phase HOP sequence offset MASTER BD_ADDR FH/TDD Channel f(2k) f(2k+1) f(2k+2) master t slave t 625 µs 25

26 Multi-slot Packets 625 µs f(k) f(k+1) f(k+2) f(k+3) f(k+4) f(k+5) f(k) f(k+3) f(k+4) f(k+5) f(k) f(k+5) Packet Format access code packet header payload 26

27 Access Code BCH LAP BRK PREAMBLE SYNC WORD TRAILER LSB MSB Access Code Types Device Access Code (DAC): unit identifier derived from unit LAP Channel Access Code (CAC): channel identifier derived from master LAP Inquiry Access Code (IAC): reserved identifier derived from reserved address 27

28 Packet Header AM_ADDR TYPE FLOW ARQN SEQN HEC parameter AM_ADDR TYPE FLOW ARQN SEQN HEC information slave active member address payload type LC flow control ACK/NAK retransmit ordering header error check Error Correction Forward-Error Correction (FEC) 1/3 rate: bit-repeat code 2/3 rate: (15,10) shortened Hamming code Automatic Retransmission Query (ARQ) 1-bit fast ACK/NAK 1-bit sequence number header piggy-backing 28

29 ARQ (I) RX CRC check TX ACK/NAK ACK/NAK retransmission new ARQ (II) MASTER A B B X C SLAVE 1 G F H SLAVE 2 Z Z NAK ACK 29

30 Physical Link Definition (I) Purpose: multi-media support Mixing: circuit switching packet switching Physical Link Definition (II) Synchronous Connection-Oriented (SCO) Link circuit switching symmetric, synchronous services slot reservation at fixed intervals Asynchronous Connection-Less (ACL) Link packet switching (a)symmetric, asynchronous services polling access scheme 30

31 Mixed Link Example MASTER SCO ACL SCO ACL ACL SCO SCO ACL SLAVE 1 SLAVE 2 SLAVE 3 Packet Types SEGMENT TYPE SCO link ACL link NULL POLL FHS DM1 HV1 HV2 HV3 DV NULL POLL FHS DM1 DH1 AUX1 DM3 DH3 DM5 DH5 31

32 Link Control Packets ID packet IQ packet NULL packet POLL packet FHS packet Data Rates (kb/s) TYPE symmetric asymmetric DM DH DM DH DM DH

33 State Transition Diagram Page Scan unit clock k k+1 k s scanf(k) sleep f(k+1) f(k+2) ms 33

34 Page Transmission f(k) f(k+1) f (k) f (k+1) f(k+2) f(k+3) ID TX RX TX t µs 1250 µs Page Trains A f(k-8) f(k-7) f(k) f(k+1) f(k+7) B f(k-16) f(k-15) f(k-9) f(k+8) f(k+15) 34

35 Page Response f(k) f(k+1) f (k) f (k+1) f(k+2) f(k+2) f(m) MASTER FHS ID ID ID ID f(k+1) SLAVE 625 µs Inquiry 1.25ms INQUIRER train A A A A A B A A A 10 ms STANDBY scan f(k) A sleep RAND1 f(k) f(k+1) f(k+1) f(k+2) A A sleep RAND2 A A ms FHS FHS 35

36 Inquiry Response f(k) f(k+1) f (k) f (k+1) f(k+4) IQ IQ IQ f(k+1) FHS 625 µs Connection Setup 1.25ms MASTER train A A A A B B 10 ms FHS CONNECTION SLAVE scan f(k) B sleep f(k+1) B ms 36

37 Low Energy Consumption Stand-by modes Low-voltage RF duty cycle % RX sleep Operational States Stand-by, Scan Page, Inquiry Connection -active - hold -sniff - park 37

38 Active Park Standby master active slave parked slave standby Sniff Example MASTER ACL ACL ACL lost SLAVE 1 SNIFF INTERVAL SLAVE 2 38

39 Park Mode BEACON PM_ADDR active slave master parked slaves Park Example PARK INTERVAL MASTER BC ACL ACL BC SLAVE X SLAVE 2 SLAVE Y 39