1. Introduction to Mobile Communications TCOM 552, Lecture #9 Hung Nguyen, Ph.D. 06 November, 2006

2. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 2Outline Wireless LAN Technology (Chapter 13) WLAN Standards (Chapter 14)

3. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 3 Wireless LAN Applications LAN Extension Cross-building interconnect Nomadic Access Ad hoc networking

4. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 4 LAN Extension Wireless LAN linked into a wired LAN on same premises –Wired LAN Backbone Support servers and stationary workstations – Wireless LAN Stations in large open areas Manufacturing plants, stock exchange trading floors, and warehouses

5. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 5 Cross-Building Interconnect Connect LANs in nearby buildings –Wired or wireless LANs Point-to-point wireless link is used Devices connected are typically bridges or routers

6. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 6 Nomadic Access Wireless link between LAN hub and mobile data terminal equipped with antenna –Laptop computer or notepad computer Uses: –Transfer data from portable computer to office server –Extended environment such as campus

7. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 7 Wireless LAN Infrastructure

8. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 8 Ad Hoc Networking Temporary peer-to-peer network set up to meet immediate need Example: –Group of employees with laptops convene for a meeting; employees link computers in a temporary network for duration of meeting

9. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 9 Ad Hoc LAN

10. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 10 Wireless LAN Requirements Throughput Number of nodes Connection to backbone LAN Service area Battery power consumption Transmission robustness and security Collocated network operation License-free operation Handoff/roaming Dynamic configuration

11. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 11 Wireless LAN Categories Infrared (IR) LANs Spread spectrum LANs Narrowband microwave

12. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 12 Strengths and Weaknesses of Infrared Over Microwave Radio Spectrum for infrared virtually unlimited –Possibility of high data rates Infrared spectrum unregulated Equipment inexpensive and simple Reflected by light-colored objects –Ceiling reflection for entire room coverage Doesn’t penetrate walls –More easily secured against eavesdropping –Less interference between different rooms

13. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 13 Drawbacks of Infrared Medium Indoor environments experience infrared background radiation –Sunlight and indoor lighting –Ambient radiation appears as noise in an infrared receiver –Transmitters of higher power required Limited by concerns of eye safety and excessive power consumption –Limits range

14. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 14 IR Data Transmission Techniques Directed Beam Infrared Ominidirectional Diffused

15. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 15 Directed Beam Infrared Used to create point-to-point links Range depends on emitted power and degree of focusing Focused IR data link can have range of kilometers –Cross-building interconnect between bridges or routers

16. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 16Omni-directional Single base station within line of sight of all other stations on LAN Station typically mounted on ceiling Base station acts as a multiport repeater –Ceiling transmitter broadcasts signal received by IR transceivers –IR transceivers transmit with directional beam aimed at ceiling base unit

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18. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 18Diffused All IR transmitters focused and aimed at a point on diffusely reflecting ceiling IR radiation strikes ceiling –Reradiated omnidirectionally –Picked up by all receivers

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20. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 20 Spread Spectrum LAN Configuration Multiple-cell arrangement (Figure 13.2 next) Within a cell, either peer-to-peer or hub Peer-to-peer topology –No hub –Access controlled with MAC algorithm CSMA: Carrier Sense Multiple Access –Appropriate for Ad Hoc LANs

21. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 21 Multiple-cell Wireless LAN CM: Control Module UM: User Module

22. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 22 Spread Spectrum LAN Configuration Hub topology –Mounted on the ceiling and connected to backbone –May control access –May act as multiport repeater –Automatic handoff of mobile stations –Stations in cell either: Transmit to / receive from hub only Broadcast using omnidirectional antenna

23. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 23 Narrowband Microwave LANs Use of a microwave radio frequency band for signal transmission Relatively narrow bandwidth Licensed Unlicensed

24. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 24 Licensed Narrowband RF Licensed within specific geographic areas to avoid potential interference Motorola holds 600 licenses (1,200 frequencies) in 18-GHz range –Covers all metropolitan areas –Can assure that independent LANs in nearby locations don’t interfere –Encrypted transmissions prevent eavesdropping

25. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 25 Unlicensed Narrowband RF RadioLAN introduced narrowband wireless LAN in 1995 –Uses unlicensed ISM spectrum –Used at low power (0.5 watts or less) –Operates at 10 Mbps in the 5.8-GHz band –Range = 50 m to 100 m

26. IEEE 802.11 Wireless LAN Standard

27. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 27 IEEE 802 Protocol Layers

28. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 28 802.11 Physical Layer Standard

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30. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 30 Pulse Position Modulation The location of the pulse within the specified pulse frame indicates what was sent Example

31. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 31 Gaussian Frequency Shift Keying GFSK is a type of Frequency Shift Keying modulation that utilizes a Gaussian filter to smooth positive/negative frequency deviations, which represent a binary 1 or 0. It is used by DECT and Bluetooth. For Bluetooth the minimum deviation is 115 kHz.

32. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 32 Protocol Architecture Functions of physical layer: –Encoding/decoding of signals (PSK, QAM, etc…) –Preamble generation/removal (for synchronization) –Bit transmission/reception –Includes specification of the transmission medium

33. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 33 IEEE 802.11 Services

34. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 34 Protocol Architecture Functions of medium access control (MAC) layer: –On transmission, assemble data into a frame with address and error detection fields –On reception, disassemble frame and perform address recognition and error detection –Govern access to the LAN transmission medium Functions of logical link control (LLC) Layer: –Provide an interface to higher layers and perform flow and error control

35. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 35 Separation of LLC and MAC The logic required to manage access to a shared-access medium not found in traditional layer 2 data link control For the same LLC, several MAC options may be provided

36. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 36 MAC Frame Format MAC control –Contains Mac protocol information Destination MAC address –Destination physical attachment point Source MAC address –Source physical attachment point CRC –Cyclic redundancy check

37. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 37 Logical Link Control Characteristics of LLC not shared by other control protocols: –Must support multi-access, shared-medium nature of the link –Relieved of some details of link access by MAC layer

38. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 38 LLC Services Unacknowledged connectionless service –No flow- and error-control mechanisms –Data delivery not guaranteed Connection-mode service –Logical connection set up between two users –Flow- and error-control provided Acknowledged connectionless service –Cross between previous two –Datagrams acknowledged –No prior logical setup

39. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 39 Differences between LLC and HDLC LLC uses asynchronous balanced mode of operation of HDLC (type 2 operation) LLC supports unacknowledged connectionless service (type 1 operation) LLC supports acknowledged connectionless service (type 3 operation) LLC permits multiplexing by the use of LLC service access points (LSAPs)

40. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 40 IEEE 802.11 Architecture Distribution system (DS) Access point (AP) Basic service set (BSS) –Stations competing for access to shared wireless medium –Isolated or connected to backbone DS through AP Extended service set (ESS) –Two or more basic service sets interconnected by DS

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42. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 42 Distribution of Messages Within a DS Distribution service –Used to exchange MAC frames from station in one BSS to station in another BSS Integration service –Transfer of data between station on IEEE 802.11 LAN and station on integrated IEEE 802.x LAN

43. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 43 Transition Types Based On Mobility No transition –Stationary or moves only within BSS BSS transition –Station moving from one BSS to another BSS in same ESS ESS transition –Station moving from BSS in one ESS to BSS within another ESS

44. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 44 Association-Related Services Association –Establishes initial association between station and AP Re-association –Enables transfer of association from one AP to another, allowing station to move from one BSS to another Disassociation –Association termination notice from station or AP

45. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 45 Access and Privacy Services Authentication –Establishes identity of stations to each other De-authentication –Invoked when existing authentication is terminated Privacy –Prevents message contents from being read by unintended recipient

46. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 46 IEEE 802.11 Medium Access Control MAC layer covers three functional areas: –Reliable data delivery –Access control –Security

47. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 47 Reliable Data Delivery More efficient to deal with errors at the MAC level than higher layer (such as TCP) Frame exchange protocol –Source station transmits data –Destination responds with acknowledgment (ACK) –If source doesn’t receive ACK, it retransmits frame Four frame exchange –Source issues request to send (RTS) –Destination responds with clear to send (CTS) –Source transmits data –Destination responds with ACK

48. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 48 Access Control

49. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 49 Medium Access Control Logic

50. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 50 Interframe Space (IFS) Values Short IFS (SIFS) –Shortest IFS –Used for immediate response actions Point coordination function IFS (PIFS) –Mid-length IFS –Used by centralized controller in PCF scheme when using polls Distributed coordination function IFS (DIFS) –Longest IFS –Used as minimum delay of asynchronous frames contending for access

51. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 51 IFS Usage SIFS –Acknowledgment (ACK) –Clear to send (CTS) –Poll response PIFS –Used by centralized controller in issuing polls –Takes precedence over normal contention traffic DIFS –Used for all ordinary asynchronous traffic

52. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 52 MAC Frame Format

53. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 53 MAC Frame Fields Frame Control – frame type, control information Duration/connection ID – channel allocation time Addresses – context dependant, types include source and destination Sequence control – numbering and reassembly Frame body – MSDU or fragment of MSDU Frame check sequence – 32-bit CRC

54. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 54 Frame Control Fields Protocol version – 802.11 version Type – control, management, or data Subtype – identifies function of frame To DS – 1 if destined for DS From DS – 1 if leaving DS More fragments – 1 if fragments follow Retry – 1 if retransmission of previous frame

55. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 55 Frame Control Fields Power management – 1 if transmitting station is in sleep mode More data – Indicates that station has more data to send WEP – 1 if wired equivalent protocol is implemented Order – 1 if any data frame is sent using the Strictly Ordered service

56. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 56 Control Frame Subtypes Power save – poll (PS-Poll) Request to send (RTS) Clear to send (CTS) Acknowledgment Contention-free (CF)-end CF-end + CF-ack

57. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 57 Data Frame Subtypes Data-carrying frames –Data –Data + CF-Ack –Data + CF-Poll –Data + CF-Ack + CF-Poll Other subtypes (don’t carry user data) –Null Function –CF-Ack –CF-Poll –CF-Ack + CF-Poll

58. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 58 Management Frame Subtypes Association request Association response Re-association request Re-association response Probe request Probe response Beacon

59. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 59 Management Frame Subtypes Announcement traffic indication message Dissociation Authentication De-authentication

60. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 60 Wired Equivalent Privacy

61. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 61Authentication Open system authentication –Exchange of identities, no security benefits Shared Key authentication –Shared Key assures authentication

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63. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 63 Physical Media Defined by Original 802.11 Standard Direct-sequence spread spectrum –Operating in 2.4 GHz ISM band –Data rates of 1 and 2 Mbps Frequency-hopping spread spectrum –Operating in 2.4 GHz ISM band –Data rates of 1 and 2 Mbps Infrared –1 and 2 Mbps –Wavelength between 850 and 950 nm

64. 11/06/2006 Hung Nguyen, TCOM 552, Fall 2006 64 IEEE 802.11a, 802.11b and 801.11g IEEE 802.11a –Makes use of 5-GHz band. Provides rates of 6, 9, 12, 18, 24, 36, 48, 54 Mbps –Uses orthogonal frequency division multiplexing (OFDM). Sub-carrier modulated using BPSK, QPSK, 16-QAM or 64- QAM IEEE 802.11b –Provides data rates of 5.5 and 11 Mbps –Complementary code keying (CCK) modulation scheme IEEE 802.11g –Uses 2.4 GHz band with DSSS & OFDM. Data rates from 1 to 54 Mbps. Compatible with WiFi at 11 Mbps

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