CWNA Guide to Wireless LANs, Second Edition

1. CWNA Guide to Wireless LANs, Second Edition Chapter Twelve Personal, Metropolitan, and Wide Area Wireless Networks

2. WPANs: Radio Frequency ID (RFID) Figure 12-8: RFID tag CWNA Guide to Wireless LANs, Second Edition

3. WPANs: Radio Frequency ID (continued) • Passive RFID tags: No power supply • Can be very small • Limited amount of information transmitted • Active RFID tags: Must have power source • Longer ranges/larger memories than passive tags Table 12-4: RFID tags CWNA Guide to Wireless LANs, Second Edition

4. WPANs: IrDA • Infrared Data Association • IrDA specifications include standards for physical devices and network protocols they use to communicate • Devices communicate using infrared light-emitting diodes • Recessed into device • Many design considerations affect IrDA performance CWNA Guide to Wireless LANs, Second Edition

5. WPANs: IrDA (continued) Figure 12-9: IrDA diodes in device CWNA Guide to Wireless LANs, Second Edition

6. WPANs: IrDA (continued) • IrDA drawbacks: • Designed to work like standard serial port on a personal computer, which is seldom used today • Cannot send and receive simultaneously • Strong ambient light can negatively impact transmissions • Angle and distance limitation between communicating devices CWNA Guide to Wireless LANs, Second Edition

7. Infrared • Many wireless devices, such as PDAs, use infrared (IR) technology • Two common uses of infrared wireless technology are IrDA and wireless local area networks (WLANs) CWNA Guide to Wireless LANs, Second Edition

8. Communications Models and Standards • International Organization for Standardization (ISO) began work in 1970s to develop specifications for communication by computer-based networks • Goal was to create an abstract model of networking rather than official physical standard • Completed in 1983, these conceptual specifications are known as Open System Interconnect (OSI) model CWNA Guide to Wireless LANs, Second Edition

9. Communications Model: OSI • Breaks complex functions into seven basic layers • Each layer performs specific function that involves different tasks • See Table 4-1 CWNA Guide to Wireless LANs, Second Edition

10. OSI Layers and Functions CWNA Guide to Wireless LANs, Second Edition

11. OSI Model • Tasks may be performed using hardware and software • Each layer must cooperate with layer immediately above and immediately below it • Data travels down layers from sending device, and then up layers to receiving device • See Figure 4-2 CWNA Guide to Wireless LANs, Second Edition

12. OSI Data Flow CWNA Guide to Wireless LANs, Second Edition

13. Communications Standards: IEEE 803 • Institute of Electrical and Electronics Engineers (IEEE) began Project 802 to create standards that would ensure interoperability among data networks • While OSI model is theoretical, Project 802 created standards for actual practice • Several standards emerged from Project 802 including 802.3 (Ethernet) and 802.5 (Token Ring) CWNA Guide to Wireless LANs, Second Edition

14. Project 802 • Project 802 subdivided OSI model Layer 2, Data Link, into two sublayers • Logical Link Control (LLC) • Media Access Control (MAC) • For wireless networks, defined by 802.11, IEEE also subdivided Physical layer into two parts • Physical Medium Dependent (PMD) • Physical Layer Convergence Procedure (PLCD) • See Figure 4-3 CWNA Guide to Wireless LANs, Second Edition

15. OSI Model versus IEEE Project 802 CWNA Guide to Wireless LANs, Second Edition

16. PLCP Sublayer • PMD sublayer • Includes standards for wireless medium such as IR and RF • Defines how medium transmits and receives data • PLCD sublayer • Reformats data received from MAC layer into packet or frame that PMD sublayer can transmit, as shown in Figure 4-4 • Listens to medium to determine when data can be sent CWNA Guide to Wireless LANs, Second Edition

17. PLCD Sublayer Reformats MAC Data CWNA Guide to Wireless LANs, Second Edition

18. Summary of PMD and PLCD Sublayers CWNA Guide to Wireless LANs, Second Edition

19. Network Protocol Stacks • Protocols are rules network must follow for communications to pass between devices • Protocols are also divided into layers, generally corresponding to the OSI model • Variety of network protocol stacks • Transmission Control Protocol/Internet Protocol (TCP/IP)—a standard protocol for the Internet • Internet Packet eXchange/Sequenced Packet eXchange (IPX/SPX)—an older Novell NetWare protocol • AppleTalk—used by Apple Macintosh computers CWNA Guide to Wireless LANs, Second Edition

20. Infrared WLANs • Several different IR WLANs have been developed during past 20 years • Infrared WLANs use part of electromagnetic spectrum just below visible light • IR shares these characteristics • Operates at high frequencies • Travels in straight lines • Does not penetrate physical objects CWNA Guide to Wireless LANs, Second Edition

21. Other IR Characteristics • Has an abundance of available bandwidth that is unregulated • Operates at high data rates • Is more secure than radio frequency transmissions • Avoids many kinds of interference that affect RF signals • Components are small and consume little power CWNA Guide to Wireless LANs, Second Edition

22. Other IR Characteristics • IR transmissions can be directed or diffused • Directed transmission uses a narrow beam and line of sight • Both emitter and detector must be aimed directly at one another • Diffused transmission uses a wide beam and reflected light • Both emitter and detector point at a reflection point on the ceiling • Limited to 4 Mbps with a range of 30 to 50 feet CWNA Guide to Wireless LANs, Second Edition

23. IEEE 802.11 Infrared WLANs • IEEE 802.11 outlines specifications for infrared WLANs • Uses diffused transmission • PHY layer both reformats data from PLCP layer and transmits light impulses (PMD) CWNA Guide to Wireless LANs, Second Edition

24. Diffused Infrared Physical Layer Convergence Procedure Standards • Frame size is measured in time slots rather than bits CWNA Guide to Wireless LANs, Second Edition

25. Parts of the Infrared PLCP Frame • Synchronization field allows emitter and receiver to synchronize • Start Frame Delimiter defines beginning of frame by transmitting 1001 • Data Rate value sets transmission speed CWNA Guide to Wireless LANs, Second Edition

26. Parts of the Infrared PLCP Frame • Direct Current Level Adjustment lets receiving device determine signal level CWNA Guide to Wireless LANs, Second Edition

27. Parts of the Infrared PLCP Frame • Length field indicates time to transmit entire frame • Header Error Check has value to determine if data was transmitted correctly • Data field can be from 1 to 20,000 time slots Although the current IEEE 802.11 standard allows data transmission rates of 1 or 2 Mbps, the preamble and header are always transmitted at 1 Mbps to accommodate slower devices CWNA Guide to Wireless LANs, Second Edition

28. Diffused Infrared Physical Medium Dependent Standards • PMD layer translates 1s and 0s into light pulses for transmission • A 1 bit has a higher intensity signal than a 0 bit • Transmissions at 1 Mbps use a 16-pulse position modulation (16-PPM), as shown in Table 4-4 • Transmissions at 2 Mbps use a 4-pulse modulation (4-PPM), as shown in Table 4-5 CWNA Guide to Wireless LANs, Second Edition

29. 16-PPM Values CWNA Guide to Wireless LANs, Second Edition

30. 4-PPM Values A time slot is always one nanosecond (ns) or a billionth of a second, but a 4-PPM transmission contains four times as much data as a 16-PPM transmission CWNA Guide to Wireless LANs, Second Edition

31. IrDA • Infrared Data Association (IrDA) is the most common infrared connection today • It links notebook computers, Personal Digital Assistants (PDA) handheld devices, cameras, watches, pagers, and kiosks • IrDA specifications include both physical devices and network protocols used for communication CWNA Guide to Wireless LANs, Second Edition

32. Overview • IrDA devices have common characteristics • Communicate with minimal preconfiguration • Provide point-to-point data transfer between only two devices at a time • Devices include broad range of computing and communicating technology • Inexpensive technology • Three versions of IrDA specifications are shown in Table 4-6 CWNA Guide to Wireless LANs, Second Edition

33. Three Versions of IrDA Specifications CWNA Guide to Wireless LANs, Second Edition

34. Multiple Infrared Connections • Single IrDA link can establish multiple simultaneous connections • Two IrDA devices can simultaneously send and receive mail, update calendar and contact information, and print documents • A separate program controls each activity • IrDA devices use infrared light emitting diodes (LEDs) to send and photodiodes to receive signals • See Figure 4-6 CWNA Guide to Wireless LANs, Second Edition

35. Infrared LEDs and Photodiodes CWNA Guide to Wireless LANs, Second Edition

36. Diodes in Device CWNA Guide to Wireless LANs, Second Edition

37. Design Factors Improve IrDA Communication • Transparent window in front of IR module should be flat instead of curved • Window should be violet to minimize loss of signal • Module should be recessed several millimeters into device case to minimize interference from ambient light CWNA Guide to Wireless LANs, Second Edition

38. IrDA Protocol Stack • IrDA Protocol stack has several layers CWNA Guide to Wireless LANs, Second Edition

39. Functions of the Layers of the IrDA Protocol Stack • IrDA Physical Layer Protocol (IrPHY) controls hardware • IrDA Link Access Protocol (IrLAP) encapsulates frames and defines how connections are established • IrDA Link Management Protocol (IrLMP) allows devices to detect other devices • IrDA Transport Protocol (Tiny TP) manages channels, corrects errors, divides data into packets, and reassembles original data CWNA Guide to Wireless LANs, Second Edition

40. IrDA Physical Layer Protocol (IrPHY) • IrPHY controls hardware • Function depends on which one of two standard is used • Serial Infrared (Version 1.0) • Fast Infrared (Version 1.1) CWNA Guide to Wireless LANs, Second Edition

41. Serial Infrared (Version 1.0) • SIR transmitter works like standard serial port on a PC • Figure 4-9 shows block diagram of SIR transmitter • Uses UART (Universal Asynchronous Receiver/Transmitter) chip on PC • Serial port transmits bits one after another • Parallel port transmits all eight bits as a byte • See Figure 4-10 CWNA Guide to Wireless LANs, Second Edition

42. SIR Transmitter Block Diagram CWNA Guide to Wireless LANs, Second Edition

43. Parallel and Serial Transmission CWNA Guide to Wireless LANs, Second Edition

44. Functions of the UART • Converts bytes into a single serial bit stream for outbound transmission • Converts serial bit stream into parallel bytes for incoming transmission • Can add an optional parity bit for error checking • Adds and removes optional start and stop delineators called start and stop bits CWNA Guide to Wireless LANs, Second Edition

45. Functions of the UART • Provides some buffering of data to keep computer and the serial device coordinated • May handle other interrupt and device management to coordinate speed of computer and device CWNA Guide to Wireless LANs, Second Edition

46. UART Frame CWNA Guide to Wireless LANs, Second Edition

47. NRZ with Same Bit Transmitted • Standard RS-232 serial ports can use NRZ (non-return-to-zero) techniques that keep output level the same for the entire bit period CWNA Guide to Wireless LANs, Second Edition

48. Return-to-Zero, Inverted (RZI) • IrDA devices cannot use NRZ technology • They use RZI that uses the inverse of RZ • RZI increases voltage for a 0 bit and no voltage for a 1 bit • UARTS have a 16x clock cycle, as shown in Figure 4-13 CWNA Guide to Wireless LANs, Second Edition

49. IrDA SIR Transmission CWNA Guide to Wireless LANs, Second Edition

50. Fast Infrared (Version 1.1) • Specifies data transfer at 4 Mbps • Retains backward compatibility with SIR devices • Figure 4-14 shows block diagram of FIR transmission CWNA Guide to Wireless LANs, Second Edition