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CWNA Guide to Wireless LANs, Second Edition Chapter Twelve Personal, Metropolitan, and Wide Area Wireless Networks WPANs: Radio Frequency ID (RFID) Figure 12-8: RFID tag CWNA Guide to Wireless LANs, Second Edition 2 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 3 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 4 WPANs: IrDA (continued) Figure 12-9: IrDA diodes in device CWNA Guide to Wireless LANs, Second Edition 5 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 6 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 7 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 8 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 9 OSI Layers and Functions CWNA Guide to Wireless LANs, Second Edition 10 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 11 OSI Data Flow CWNA Guide to Wireless LANs, Second Edition 12 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 13 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 14 OSI Model versus IEEE Project 802 CWNA Guide to Wireless LANs, Second Edition 15 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 16 PLCD Sublayer Reformats MAC Data CWNA Guide to Wireless LANs, Second Edition 17 Summary of PMD and PLCD Sublayers CWNA Guide to Wireless LANs, Second Edition 18 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 19 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 20 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 21 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 22 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 23 Diffused Infrared Physical Layer Convergence Procedure Standards • Frame size is measured in time slots rather than bits CWNA Guide to Wireless LANs, Second Edition 24 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 25 Parts of the Infrared PLCP Frame • Direct Current Level Adjustment lets receiving device determine signal level CWNA Guide to Wireless LANs, Second Edition 26 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 27 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 28 16-PPM Values CWNA Guide to Wireless LANs, Second Edition 29 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 30 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 31 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 32 Three Versions of IrDA Specifications CWNA Guide to Wireless LANs, Second Edition 33 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 34 Infrared LEDs and Photodiodes CWNA Guide to Wireless LANs, Second Edition 35 Diodes in Device CWNA Guide to Wireless LANs, Second Edition 36 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 37 IrDA Protocol Stack • IrDA Protocol stack has several layers CWNA Guide to Wireless LANs, Second Edition 38 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 39 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 40 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 41 SIR Transmitter Block Diagram CWNA Guide to Wireless LANs, Second Edition 42 Parallel and Serial Transmission CWNA Guide to Wireless LANs, Second Edition 43 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 44 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 45 UART Frame CWNA Guide to Wireless LANs, Second Edition 46 NRZ with Same Bit Transmitted • Standard RS-232 serial ports can use NRZ (non-returnto-zero) techniques that keep output level the same for the entire bit period CWNA Guide to Wireless LANs, Second Edition 47 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 48 IrDA SIR Transmission CWNA Guide to Wireless LANs, Second Edition 49 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 50 FIR Transmitter Block Diagram CWNA Guide to Wireless LANs, Second Edition 51 IrDA FIR Transmission • FIR uses 4 PPM • Only two bits are transmitted • Receiving device determines transmitted bit by locating pulse within time slot CWNA Guide to Wireless LANs, Second Edition 52 Other Considerations • Several other factors influence infrared transmission, including – Latency – Ambient light – Deflection angle CWNA Guide to Wireless LANs, Second Edition 53 Half-Duplex and Latency • IrDA devices cannot send and receive at same time – Their communication mode is half-duplex • A time delay is required for device to stop transmitting and get ready to receive – This delay is called latency or receiver set-up time – IrDA specifications allow 10 ms latency CWNA Guide to Wireless LANs, Second Edition 54 Ambient Light • IrDA specifies test methods for measuring data integrity of an IrDA connection under electromagnetic fields, sunlight, incandescent light, and fluorescent light • Lux is a photometric measurement of light intensity • If lux values exceed standard, devices may still communicate, but they must be placed closer to each other CWNA Guide to Wireless LANs, Second Edition 55 Deflection Angle • How sending and receiving IrDA devices align is important • Devices with a deflection angle up to 15 degrees can be 3 feet apart, as shown in Figure 4-16 • With deflection angle between 15 and 30 degrees, devices must be closer together • With a deflection angle over 30 degrees, infrared transmission will be impossible CWNA Guide to Wireless LANs, Second Edition 56 Deflection Angle CWNA Guide to Wireless LANs, Second Edition 57 Wireless Metropolitan Area Networks • Cover an area of up to 50 kilometers (31 miles) • Used for two primary reasons: – Alternative to an organization’s wired backhaul connection • i.e., T1, T3, T4 lines – Fiber Optics • Very expensive to install backhaul connections • Often less expensive to use a WMAN to link remote sites CWNA Guide to Wireless LANs, Second Edition 58 Wireless Metropolitan Area Networks (continued) • Used for two primary reasons (continued): – Overcome last mile connection • Connection that begins at a fast Internet service provider, goes through local neighborhood, and ends at the home or office • Slower-speed connection – Bottleneck CWNA Guide to Wireless LANs, Second Edition 59 Wireless Metropolitan Area Networks: Free Space Optics • Optical, wireless, point-to-point, line-of-sight wireless technology – Able to transmit at speed comparable to Fiber Optics – Transmissions sent by low-powered IR beams • Advantages compared to fiber optic and RF: – – – – Lower installation costs Faster installation Scaling transmission speed Good security • Atmospheric conditions can affect transmission CWNA Guide to Wireless LANs, Second Edition 60 Wireless Metropolitan Area Networks: Local Multipoint Distribution Service (LMDS) • LMDS provides wide variety of wireless services – High-frequency, low-powered RF waves have limited range – Point-to-multipoint signal transmission • Signals transmitted back are point-to-point – Voice, data, Internet, and video traffic – Local carrier determines services offered • LMDS network is composed of cells – Cell size affected by line of site, antenna height, overlapping cells, and rainfall CWNA Guide to Wireless LANs, Second Edition 61 Wireless Metropolitan Area Networks: LMDS (continued) Figure 12-11: LMDS cell CWNA Guide to Wireless LANs, Second Edition 62 Wireless Metropolitan Area Networks: Multichannel Multipoint Distribution Service (MMDS) • Many similarities to LMDS – Differs in area of transmission – Higher downstream transmission, lower upstream transmission, greater range • In homes, alternative to cable modems and DSL service • For businesses, alternative to T1 or fiber optic connections • MMDS hub typically located at a very high point – On top of building, towers, mountains CWNA Guide to Wireless LANs, Second Edition 63 Wireless Metropolitan Area Networks: MMDS (continued) • Hub uses point-to-multipoint architecture – Multiplexes communications to multiple users – Tower has backhaul connection • MMDS uses cells – Single MMDS cell as large as 100 LDMS cells • Receiving end uses pizza box antenna • Advantages: – Transmission range, cell size, low vulnerability to poor weather conditions • Still requires line-of-site, not encrypted CWNA Guide to Wireless LANs, Second Edition 64 Wireless Metropolitan Area Networks: IEEE 802.16 (WiMAX) • High potential – Can connect IEEE 802.11 hotspots to Internet – Can provide alternative to cable and DSL for last mile connection – Up to 50 kilometers of linear service area range – Does not require direct line of sight – Provides shared data rates up to 70 Mbps • Uses scheduling system – Device competes once for initial network entry CWNA Guide to Wireless LANs, Second Edition 65 Wireless Metropolitan Area Networks: IEEE 802.16 (continued) • Currently addresses only devices in fixed positions – 802.16e will add mobile devices to the standard • IEEE 802.20 standard: Sets standards for mobility over large areas – Will permit users to roam at high speeds • WiMAX base stations installed by a wireless Internet service provider (wireless ISP) can send high-speed Internet connections to homes and businesses in a radius of up to 50 km (31 miles) CWNA Guide to Wireless LANs, Second Edition 66 Wireless Wide Area Networks (WWANS) • Wireless networks extending beyond 50 kilometers (31 miles) • Two primary technologies: – Digital cellular telephony – Satellites CWNA Guide to Wireless LANs, Second Edition 67 Digital Cellular Telephony • Two keys to cellular telephone networks: – Coverage area divided into cells • • • • Cell transmitter at center Mobile devices communicate with cell center via RF Transmitters connected to base station, Each base station connected to a mobile telecommunications switching office (MTSO) – Link between cellular and wired telephone network – All transmitters and cell phones operate at low power • Enables frequency reuse CWNA Guide to Wireless LANs, Second Edition 68 Digital Cellular Telephony (continued) Figure 12-13: Frequency reuse CWNA Guide to Wireless LANs, Second Edition 69 Satellites • Satellite use falls into three broad categories: – Acquire scientific data, perform research – Examine Earth • Military and weather satellites – “Reflectors” • Relay signals • Communications, navigation, broadcast CWNA Guide to Wireless LANs, Second Edition 70 Satellites (continued) • Satellite systems classified by type of orbit: – Low earth orbiting (LEO): Small area of earth coverage • Over 225 satellites needed for total coverage of earth • Must travel very fast – Medium earth orbiting (MEO): Larger area of coverage than LEO • Do not need to travel as fast – Geosynchronous earth orbiting (GEO): orbit matches earth’s rotation • “Fixed” position • Very large coverage area CWNA Guide to Wireless LANs, Second Edition 71 Satellites (continued) Figure 12-14: LEO coverage area CWNA Guide to Wireless LANs, Second Edition 72 The Future of Wireless Networks • IEEE 802.11 subcommittees currently at work: – 802.11d: Supplementary to 802.11 MAC layer • Promote worldwide use of 802.11 WLANs – 802.11f: Inter-Access Point Protocol (IAPP) • Will assist with faster handoff from one AP to another – 802.11h: Supplement to MAC layer to comply with European regulations for 5 GHz WLANs – 802.11j: Incorporates Japanese regulatory extensions to 802.11a standard – 802.11s: Defines a mesh wireless network • Devices configure themselves and are intelligent CWNA Guide to Wireless LANs, Second Edition 73 Summary • WPANs encompass technology that is designed for portable devices, typically PDAs, cell phones, and tablet or laptop computers at transmission speeds lower than the other types of networks • The IEEE 802.15 standards address wireless personal area networks • RFID is not a standard but is a technology that uses RF tags to transmit information • IrDA technology uses infrared transmissions to transmit data at speeds from 9,600 bps to 16 Mbps CWNA Guide to Wireless LANs, Second Edition 74 Summary (continued) • FSO is an optical, wireless, point-to-point wireless metropolitan area network technology • LMDS can provide a wide variety of wireless services, including high-speed Internet access, real-time multimedia file transfer, remote access to local area networks, interactive video, video-ondemand, video conferencing, and telephone • MMDS has many of similarities to LMDS, yet has a longer distance range CWNA Guide to Wireless LANs, Second Edition 75 Summary (continued) • The IEEE 802.16 (WiMAX) standard holds great promise for providing higher throughput rates for fixed location and mobile users • Wireless wide area network (WWAN) technology encompasses digital cellular telephony and satellite • The future of wireless networks is hard to predict, but most experts agree that wireless networks will be faster, more global, and easier to use in the years ahead CWNA Guide to Wireless LANs, Second Edition 76