1. 1 Kyung Hee University Chapter 15 Wireless LANs

2. 2 Kyung Hee University IEEE 802 Standards Working Groups WiMAX, an acronym that stands for Worldwide Interoperability for Microwave Access(802.16) WiFi (Wireless Fidelity) : 802.11

3. 3 Kyung Hee University Introduction  Architecture  Physical Layer  MAC Layer  Addressing Mechanism

4. 4 Kyung Hee University 15.1 IEEE 802.11 - Architecture  Basic Service Set (BSS)  Extended Service Set (ESS)

5. 5 Kyung Hee University Basic Service Set made up of stationary or mobile wireless stations, and possibly a central base station (access point) BSS without an AP is stand-alone, cannot send data to other BSSs

6. 6 Kyung Hee University ESS – Extended Service Set  Made up of two or more BSSs with APs – connected through a distribution system (usually a wired LAN)

7. 7 Kyung Hee University Station Types  No-transition mobility – either stationary or moving only inside a BSS  BSS-transition mobility – can move from one BSS to another, confined to one ESS  ESS-transition mobility – can move from one ESS to another

8. 8 Kyung Hee University Physical layer specifications  802.11 defines the specs for the conversion of bits to a signal

9. 9 Kyung Hee University FHSS – Frequency hopping spread spectrum  sender sends on one carrier frequency for a short amount of time, hops to another frequency for the same time, then another, and so on, eventually the cycle is repeated  makes it difficult for unauthorized person to make sense of data  2.4 GHz industrial, scientific, and medical (ISM) band – 79 subbands of 1MHz  modulation is FSK (two-level or four-level)

10. 10 Kyung Hee University Frequency-Hopping example 

11. 11 Kyung Hee University DSSS – direct sequence spread spectrum  Each bit sent is replaced by a chip code (similar to CDMA, but this is at the physical layer, not a multiple- access data link layer method)  2.4 GHz ISM band  Modulation is PSK (BPSK or QPSK)

12. 12 Kyung Hee University 802.11  802.11 Infrared  Two capacities 1 Mbps or 2 Mbps.  Range is 10 to 20 meters and cannot penetrate walls.  Does not work outdoors.  802.11 FHSS (Frequence Hopping Spread Spectrum)  The main issue is multipath fading.  79 non-overlapping channels, each 1 Mhz wide at low end of 2.4 GHz ISM band.  Same pseudo-random number generator used by all stations.  Dwell time: min. time on channel before hopping (400msec).

13. 13 Kyung Hee University 801.11a,b,g  802.11a OFDM – orthogonal frequency division multiplexing  5-GHz ISM band  48 subbands for sending 48 groups of bits at a time, 4 subbands for control information  PSK for 18Mbps and QAM for 54 Mbps  802.11b HR-DSSS – high-rate direct sequence spread spectrum  2.4 GHz band  similar to DSSS except for encoding, complementary code keying (CCK), encodes 4 or 8 bits to one CCK symbol  modulation BPSK and QPSK  4 data rates (1, 2, 5.5, and 11 Mbps) : DSSS for 1, 2 Mbps, BPSKllfor 5.5, QPSK for 11 Mbps  Range is 7 times greater than 11a.  802.11b and 11a are incompatible!!

14. 14 Kyung Hee University 801.11a,b,g (cont’d)  802.11g OFDM  2.4 GHz band  54-Mbps data rate  Is backward compatible with 802.11b.

15. 15 Kyung Hee University MAC layers in IEEE 802.11 standard PCF : Point Coordination Function DCF : Distributed Coordination Function

16. 16 Kyung Hee University CSMA/CA  Cannot implement CSMA/CD:  collision detection implies the ability to send and receive at the same time, which implies costly stations and increased bandwidth requirements  collision may not be detected because of a hidden terminal  distance could cause signal fading which could prevent a station from hearing a collision

17. 17 Kyung Hee University Hidden and Exposed Terminals  (a)The hidden station problem (b) The exposed station problem

18. 18 Kyung Hee University CSMA/CA flowchart

19. 19 Kyung Hee University CSMA/CA and NAV DIFS – distributed interframe spreadNAV – network allocation vector SIFS – short interframe spreadcollision only occurs during RTS – request to sendhandshake period (RTS, CTS) CTS – clear to send

20. 20 Kyung Hee University Frame format

21. 21 Kyung Hee University Subfields in FC(frame control) field FieldExplanation VersionThe current version is 0. TypeType of information: management (00), control (01), or data (10). SubtypeDefines the subtype of each type (see ). To DSDefined later. From DSDefined later. More flagWhen set to 1, means more fragments. RetryWhen set to 1, means retransmitted frame. Pwr mgtWhen set to 1, means station is in power management mode. More dataWhen set to 1, means station has more data to send. WEPWired equivalent privacy. When set to 1, means encryption implemented. RsvdReserved.

22. 22 Kyung Hee University Control frames

23. 23 Kyung Hee University Values of subfields in control frames  type field : 01 SubtypeMeaning 1011 Request to send (RTS) 1100 Clear to send (CTS) 1101 Acknowledgment (ACK)

24. 24 Kyung Hee University Subfields in FC field  To DS From DS Address 1 Address 2 Address 3 Address 4 00 Destination station Source station BSS ID N/A 01 Destination station Sending AP Source station N/A 10 Receiving AP Source station Destination station N/A 11 Receiving AP Sending AP Destination station Source station

25. 25 Kyung Hee University Addressing mechanism: case 1 To DS = 0 and From DS = 0 Frame is not going to a distribution system Frame is going from one station in a BSS to another ACK sent to original sender

26. 26 Kyung Hee University Addressing mechanism: case 2  To DS = 0 and From DS = 1  Frame is coming from a distribution system  Frame is coming from an AP and going to a station  ACK sent to AP

27. 27 Kyung Hee University Addressing mechanism: case 3  To DS = 1 and From DS = 0  Frame is going to a distribution system  Frame is coming from a station to an AP  ACK sent to original station  address 3 contains final destination of frame

28. 28 Kyung Hee University Addressing mechanism: case 4  To DS = 1 and From DS = 1  Distribution system is wireless  Frame is coming from an AP going to another AP

29. 29 Kyung Hee University 15.2 Bluetooth Architecture Radio Layer Baseband Layer Other Upper Layers L2CAP Layer

30. 30 Kyung Hee University - Architecture - Two Types of Networks  Piconets  Scatternet

31. 31 Kyung Hee University Piconet  up to eight stations, one is the master, rest are slaves  slaves synchronize their clocks and hopping sequence with master  only one master  communication between master and slave can be 1-1 or 1-many  can have up to eight additional slaves in parked state  slave in parked state is synchronized, but cannot communicate

32. 32 Kyung Hee University Scatternet  scatternet – combined piconets  slave in one piconet can be master in another

33. 33 Kyung Hee University Bluetooth layers

34. 34 Kyung Hee University Radio Layers  roughly equivalent to the physical layer of the Internet model  2.4-GHz ISM band  FHSS – frequency hopping spread spectrum  modulation – sophisticated version of FSK, called GFSK (FSK w/ Gaussian bandwidth filtering)

35. 35 Kyung Hee University Baseband Layer  roughly equivalent to MAC sublayer in LANs  access method is TDMA  TDD-TDMA (time division duplexing TDMA) – a kind of half duplex communication  single slave communication – master uses even number slots, slave uses odd numbered  multiple slave communication – master uses even number slots, slave sends in the next odd-numbered slot if the packet in the previous slot was addressed to it

36. 36 Kyung Hee University Single-slave Communication

37. 37 Kyung Hee University Multiple-slave communication

38. 38 Kyung Hee University Physical Links  SCO – synchronous connection oriented link – avoiding latency is more important than integrity – damaged packet is never retransmitted  ACL – asynchronous connectionless link – data integrity is more important than avoiding latency – if packet is damaged, it is retransmitted

39. 39 Kyung Hee University Frame Format Types

40. 40 Kyung Hee University L2CAP data packet format  Logical link control and adaptation protocol – roughly equivalent to the LLC sublayer in LANs  used for data exchange on an ACL link  specific duties: multiplexing, segmentation and reassembly, quality of service, and group management

41. 41 Kyung Hee University Questions !