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Wireless A to Z review-bloggers.blogspot.com

  1. 1. Wireless A to Z
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  3. 3. Wireless A to Z Nathan J. Muller McGraw-HillNew York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto
  4. 4. Copyright © 2003 by The McGraw-Hill Companies, Inc. All rights reserved. Manufacturedin the United States of America. Except as permitted under the United States Copyright Actof 1976, no part of this publication may be reproduced or distributed in any form or by anymeans, or stored in a database or retrieval system, without the prior written permission ofthe publisher.0-07-142918-2The material in this eBook also appears in the print version of this title: 0-07-141088-0.All trademarks are trademarks of their respective owners. Rather than put a trademarksymbol after every occurrence of a trademarked name, we use names in an editorial fash-ion only, and to the benefit of the trademark owner, with no intention of infringement ofthe trademark. Where such designations appear in this book, they have been printed withinitial caps.McGraw-Hill eBooks are available at special quantity discounts to use as premiums andsales promotions, or for use in corporate training programs. For more information, pleasecontact George Hoare, Special Sales, at george_hoare@mcgraw-hill.com or (212) 904-4069.TERMS OF USEThis is a copyrighted work and The McGraw-Hill Companies, Inc. (“McGraw-Hill”) andits licensors reserve all rights in and to the work. Use of this work is subject to these terms.Except as permitted under the Copyright Act of 1976 and the right to store and retrieveone copy of the work, you may not decompile, disassemble, reverse engineer, reproduce,modify, create derivative works based upon, transmit, distribute, disseminate, sell, pub-lish or sublicense the work or any part of it without McGraw-Hill’s prior consent. Youmay use the work for your own noncommercial and personal use; any other use of thework is strictly prohibited. Your right to use the work may be terminated if you fail tocomply with these terms.THE WORK IS PROVIDED “AS IS”. McGRAW-HILL AND ITS LICENSORS MAKENO GUARANTEES OR WARRANTIES AS TO THE ACCURACY, ADEQUACY ORCOMPLETENESS OF OR RESULTS TO BE OBTAINED FROM USING THE WORK,INCLUDING ANY INFORMATION THAT CAN BE ACCESSED THROUGH THEWORK VIA HYPERLINK OR OTHERWISE, AND EXPRESSLY DISCLAIM ANYWARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TOIMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICU-LAR PURPOSE. McGraw-Hill and its licensors do not warrant or guarantee that the func-tions contained in the work will meet your requirements or that its operation will be unin-terrupted or error free. Neither McGraw-Hill nor its licensors shall be liable to you oranyone else for any inaccuracy, error or omission, regardless of cause, in the work or forany damages resulting therefrom. McGraw-Hill has no responsibility for the content ofany information accessed through the work. Under no circumstances shall McGraw-Hilland/or its licensors be liable for any indirect, incidental, special, punitive, consequentialor similar damages that result from the use of or inability to use the work, even if any ofthem has been advised of the possibility of such damages. This limitation of liability shallapply to any claim or cause whatsoever whether such claim or cause arises in contract,tort or otherwise.DOI: 10.1036/0071429182
  5. 5. To my brother Jim On his retirement from theSouth Burlington, Vermont, Police Department
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  7. 7. For more information about this title, click here. CONTENTS Preface xiA 1 Access Points 1 Advanced Mobile Phone Service 6 Air-Ground Radiotelephone Service 8 Amateur Radio Service 12B 17 Basic Exchange Telephone Radio Service 17 Bluetooth 18 Bridges 27C 31 Cell Sites 31 Cellular Data Communications 34 Cellular Telephones 36 Cellular Voice Communications 48 Citizens Band Radio Service 55 Code Division Multiple Access 59 Competitive Local Exchange Carriers 67 Cordless Telecommunications 70D 75 Data Compression 75 Decibel 80 Digitally Enhanced Cordless Telecommunications 82 Direct Broadcast Satellite 87E 95 Enhanced Data Rates for Global Evolution 95 viiCopyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  8. 8. viii CONTENTSF 97 Family Radio Service 97 Federal Communications Commission 99 Fixed Wireless Access 103 Fraud Management Systems 105 Frequency Division Multiple Access 119G 123 Global Maritime Distress and Safety System 123 General Mobile Radio Service 125 General Packet Radio Service 128 Global Positioning System 131 Global System for Mobile (GSM) Telecommunications 139H 149 Hertz 149 Home Radio-Frequency (RF) Networks 152I 159 i-Mode 159 Incumbent Local Exchange Carriers 161 Infrared Networking 164 Integrated Digital Enhanced Network 172 Interactive Television 175 Interactive Video and Data Service 181 Interexchange Carriers 183 International Mobile Telecommunications 186L 195 Laser Transmission 195 Local Multipoint Distribution Service 198 Low-Power FM Radio Service 205 Low-Power Radio Service 208M 211 Maritime Mobile Service 211 Microwave Communications 213 Mobile Telephone Switching Office 217 Multichannel Multipoint Distribution Service 220 Multichannel Video Distribution and Data Service 223O 225 Over-the-Air Service Activation 225
  9. 9. CONTENTS ixP 229 Paging 229 PCS 1900 238 Peer-to-Peer Networks 243 Personal Access Communications Systems 251 Personal Air Communications Technology 254 Personal Communications Services 262 Personal Digital Assistants 266 Personal Handyphone System 273 Private Land Mobile Radio Services 279R 287 Radio Communication Interception 287 Remote Monitoring 290 Repeaters 301 Routers 304 Rural Radiotelephone Service 310S 311 Satellite Communications 311 Short Messaging Service 322 Software-Defined Radio 326 Specialized Mobile Radio 332 Spectrum Auctions 334 Spectrum Planning 338 Spread-Spectrum Radio 341T 349 Telegraphy 349 Telemetry 354 Time Division Multiple Access 360U 367 Ultra Wideband 367 Universal Mobile Telephone Service 371V 377 Voice Cloning 377 Voice Compression 380W 389 Wired Equivalent Privacy 389 Wireless E911 392
  10. 10. x CONTENTS Wireless Application Protocol 394 Wireless Application Service Providers 401 Wireless Centrex 405 Wireless Communications Services 409 Wireless Fidelity 411 Wireless Internet Access 414 Wireless Internet Service Providers 422 Wireless Internetworking 425 Wireless Intranet Access 430 Wireless IP 434 Wireless LAN Security 437 Wireless LANs 444 Wireless Local Loops 454 Wireless Local Number Portability 464 Wireless Management Tools 465 Wireless Medical Telemetry Service 468 Wireless Messaging 470 Wireless PBX 473 Wireless Telecommunications Bureau 481 Wireless Telecommunications Investment Fraud 483 Acronyms 487 Index 519
  11. 11. PREFACEOf all the communications services available today, wirelessservices are having the most dramatic impact on our personaland professional lives, enhancing personal productivity,mobility, and security. With every new wireless product andservice, the boundary between home and office is blurredfurther, perhaps to the point that one day they will be indis-tinguishable. Instead of the flexible work schedule, wirelessproducts and services give us the capability of being “alwayson.” For a growing number of people, a true vacation consistsof shutting down communication with the rest of the world. The wireless industry worldwide is experiencing rapidinnovation, increased competition, and diversity in serviceofferings—all of which have resulted in lower prices for con-sumers and businesses. Service providers continue to fill ingaps in their national coverage through mergers, acquisi-tions, license swaps, and joint ventures. Along with thisprocess of footprint building, service providers continue todeploy their networks in an increasing number of markets,expand their digital networks, and develop pricing plans thatattract new subscribers and stimulate minutes of usage. Mobile telephony is a particularly vibrant sector, experi-encing strong growth and reaching new levels of competitivedevelopment. At year-end 2001, mobile telephony servicesgenerated over $65 billion in revenues in the United States,increased subscribers from 109.5 million to 128.5 million, andproduced a nationwide penetration rate of over 50 percent. Broadband PCS carriers and digital SMR providers con-tinue to deploy their networks. According to the FederalCommunications Commission (FCC), 268 million people, or94 percent of the total U.S. population, live in areas served xi Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  12. 12. xii PREFACEby three or more different operators offering mobile telephoneservice. Over 229 million people, or 80 percent of the U.S.population, live in counties with five or more mobile tele-phone operators competing to offer service. And 151 millionpeople, or 53 percent of the population, live in areas in whichsix different mobile telephone operators are providing service. Digital technology is now dominant in the mobile tele-phone sector. At the end of 2001, digital customers made upalmost 80 percent of the industry total, up from 72 percentat year-end 2000. In part because of competitive pressuresin the marketplace, the average price of residential mobiletelephone service declined by 5.5 percent during 2001. Theaverage revenue per minute of mobile telephone use fell 31percent between 2000 and 2001. Many mobile telephone carriers are deploying advancedwireless service network technologies such as cdma20001xRTT and General Packet Radio Service (GPRS). Thesedeployments have contributed to the further convergence ofmobile voice and data. The increased capacity on these digitalnetworks has permitted operators to offer calling plans withlarge buckets of relatively inexpensive minutes, free enhancedservices such as voice mail and caller ID, and wireless dataand mobile Internet offerings. Once solely a business tool, wireless phones are now amass-market consumer device. By some estimates, 3 to 5percent of customers use their wireless phones as their onlyphone. Though relatively few wireless customers have “cutthe cord” in the sense of canceling their wireline telephoneservice, there is growing evidence that consumers are sub-stituting wireless service for traditional phone service. It isalso estimated that 20 percent of residential customers havereplaced some wireline phone usage with wireless, and that11 percent have replaced a significant percentage. Andalmost one in five mobile telephony users regard their wire-less phone as their primary phone. Contributing to these trends is the increasing number ofmobile wireless carriers offering service plans designed tocompete directly with wireline local telephone service, many
  13. 13. PREFACE xiiiwith virtually unlimited regional calling plans. For $40 to$50 per month, subscribers get a calling plan that includes4,000 minutes (usable anytime) and the ability to roamacross several states without extra fees. Several local carriers have attributed declining access-linegrowth rates in part to substitution by wireless. The numberof residential access lines served by BellSouth, SBC, andVerizon dropped by almost 3 percent during 2001, or morethan 2.5 million lines. Verizon attributes the decline in thenumber of access lines in part to the shift to wireless phones.Nationwide, by year-end 2001, wireless had displaced anestimated 10 million access lines, primarily by consumerschoosing wireless over installing additional access lines. Wireless plans are substituting for traditional wirelinelong distance as well. Many calling plans offered by nationalwireless carriers include free nationwide long distance. Forexample, about 20 percent of AT&T’s customers, or 5 millionpeople, have replaced some wireline long-distance usage withwireless. AT&T attributes the decline in its long-distancecalling volumes and revenues in part to wireless substitution.At least one wireless operator, Cingular Wireless, advertisesits nationwide calling plans with the slogan, “Never PayLong Distance Again.” Because of national advertising and the Internet, con-sumers all over the country are educated about nationwiderate plans and services enabled by digital technology andthe prices of wireless handsets. No matter where they live,customers expect and demand the diversity of services atcompetitive rates. Wireless is having an impact in other ways. PDAs, orhandheld devices, began as electronic organizers containingpersonal information management (PIM) functions, suchas an address book, calendar, and to-do list that could be“synched” with PIM software on a user’s desktop computer.While PDAs still contain these core PIM and software fea-tures, handhelds are being repositioned as wireless commu-nication devices instead of simple organizers. All of the PDAmodels introduced by the major manufacturers since 2001
  14. 14. xiv PREFACEallow users some method of connecting to the Internet wire-lessly. Some combine the features of mobile phones and PDAfeatures into so-called “smartphones.” Compared to traditional mobile handsets, smartphonesgenerally have larger screens, more advanced graphics andprocessing capabilities, more memory, a more user-friendlyoperating system, some form of keypad, and the ability tosynch data with and download software from a desktopcomputer. Smartphones also integrate traditional mobiletelephone phone number storage and access with a PDA’saddress book so users are not required to store numbers intwo different places. These smartphones also allow messaging via the ShortMessage Service (SMS). SMS provides the ability for users tosend and receive text messages to and from mobile handsetswith maximum message length ranging from 120 to 500characters. SMS also can be used to deliver a wide range ofinformation to mobile users, including stock prices, sportscores, news headlines, weather reports, and horoscopes.Worldwide, SMS has become increasingly popular, growingto 250 billion messages sent over wireless networks world-wide in 2001. Using their existing and next-generation networks, majormobile telephone service providers offer text-based wirelessweb services via mobile telephone handsets at speeds rangingfrom approximately 14.4 kbps on 2G networks to 60 kbps onadvanced 2.5/3G wireless networks. During 2001, mobiletelephone providers expanded their data service offerings asthey began to transition their networks to higher speedtechnologies. In addition to offering wireless web service onmobile telephone handsets, several carriers offer wirelessInternet connections via wireless modem cards for PDAs andlaptop computers as well. Mobile telephone service providers offer wireless webservices that enable customers to surf web sites for news,stock quotes, traffic reports, weather forecasts, movie listings,shopping, and other text-based information. To deliver wire-less web content to wireless handset users, carriers currently
  15. 15. PREFACE xvrestrict users to less graphically enriched content. This con-serves the resources of the memory-constrained devices.However, customers who connect to the Internet via a wire-less modem card attached to a notebook computer are able toaccess the full content of the web. Many PDAs have the ability to access almost the entire con-tent of the web. For example, Pocket PC PDAs include a PDAversion of Microsoft’s Internet Explorer web browser, whichcan access any web site. While many PDAs have the potentialto access web content with their browsing software, they stillrequire a subscription to a wireless Internet Service Provider(WISP) in order to connect to the Internet via wireless links. As workers become increasingly more mobile and remote,the ability for employees outside the office to access e-mailmessages and files stored electronically on corporate serversis likely to become an increasingly more important mobiledata application. Analysts claim that giving employeesmobile access to e-mail and to data and applications storedon corporate servers are two of the most important uses ofPDAs in the enterprise market. Surveys of U.S. firms indicatethat mobile access to e-mail is the top priority. There are short-range data transmission technologies thatare gaining in popularity: infrared, Bluetooth, and WirelessFidelity (Wi-Fi). Infrared is currently used in some PDAs toallow users to transfer data between two devices. Infrared isalso the technology commonly used in remote controls andrequires line-of-sight transmission. Bluetooth enables multi-point broadcasting applications, and Wi-Fi enables devices toconnect to wireless local area networks (WLANs). Bluetooth is a technology used to establish wireless con-nectivity between electronic devices that are up to 30 ft (10 m)apart. It allows users to send signals and transfer dataamong numerous electronic devices, thus creating a personalarea network (PAN). Bluetooth uses unlicensed spectrumin the 2.4 GHz band and transmits data at speeds close to1 Mbps. Bluetooth also uses frequency hopping spread spec-trum techniques to provide enhanced communications per-formance and an initial level of transmission security.
  16. 16. xvi PREFACE Wi-Fi is another wireless networking technology shar-ing the 2.4 GHz frequency band with Bluetooth. Also calledWi-Fi, the 802.11b standard is used to connect devices toWLANs, and allows a maximum throughput of 11 Mbps. Thetechnology is being used in a number of WLAN settings,such as college campuses, business parks, office buildings,and even private homes. It is also being implemented by anumber of vendors in public places such as airports, hotels,and cafes to give users of notebook computers, handhelddevices, and smartphones wireless Internet access any-where inside those locations. Wireless technologies and services have become so popularworldwide and sufficiently sophisticated and complex as tomerit dozens of books on the topic that are published everyyear. This encyclopedia is a quick reference that clearlyexplains the essential concepts of wireless, including services,applications, protocols, network methods, developmenttools, administration and management, standards, and reg-ulation. It is designed as a companion to other books youmay want to read about wireless, providing clarification ofconcepts that may not be fully covered elsewhere. The information contained in this book, especially as itrelates to specific vendors and products, is believed to be accu-rate at the time it was written and is, of course, subject tochange with continued advancements in technology and shiftsin market forces. Mention of specific products and services isfor illustration purposes only and does not constitute anendorsement of any kind by either the author or the publisher. Nathan J. Muller
  17. 17. AACCESS POINTSAn access point (AP) provides the connection between one ormore wireless client devices and a wired local area network(LAN). The AP is usually connected to the LAN via aCategory-5 cable connection to a hub or switch. Clientdevices communicate with the AP over the wireless link, giv-ing them access to all other devices through the hub orswitch, including a router on the other side of the hub, whichprovides Internet access (Figure A-1). An AP that adheres to the IEEE 802.11b Standard foroperation over the unlicensed 2.4-GHz band supports a wire-less link with a data transfer speed of up to 11 Mbps, whilean AP that adheres to the IEEE 802.11a Standard for opera-tion over the unlicensed 5-GHz band supports a wireless linkwith a data transfer speed of up to 54 Mbps. Access pointsinclude a number of the following functions and features:G Radio power control for flexibility and ease of networking setupG Dynamic rate scaling, mobile Internet Protocol (IP) func- tionality, and advanced transmit/receive technology to enable multiple access points to serve users on the move 1 Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  18. 18. 2 ACCESS POINTS Internet Hub Router Ethernet Access Point Wireless ClientsFigure A-1 A simple configuration showing the relationship of the accesspoint to the wired and wireless segments of the network.G Built-in bridging and repeating features to connect build- ings miles apart (The use of specialty antennas increases range. The AP can support simultaneous bridging and client connections.)G Wired Equivalent Privacy (WEP), which helps protect data in transit over the wireless link between the client device and the AP, via 64-, 128-, or 256-bit encryptionG Access control list (ACL) and virtual private network (VPN) compatibility to help guard the network from intrudersG Statistics on the quality of the wireless link (Figure A-2)G Configurability using the embedded Web browser Consumer-level APs stress ease of setup and use (FigureA-3). Many products are configured with default settings
  19. 19. ACCESS POINTS 3Figure A-2 The 5-GHz DWL-5000 Access Point from D-Link Systems, Inc., keeps the client device notified of the sta-tus of the wireless link. In this case, the signal is atmaximum strength and is capable of a data transfer rate of48 Mbps.that allow the user to plug in the device and use the wirelessconnection immediately. Later, the user can play with theconfiguration settings to improve performance and set upsecurity. Although APs adhere to the IEEE 802.11 Standards, man-ufacturers can include some proprietary features thatimprove the data transfer speed of the wireless link. Forexample, one vendor advertises a “turbo mode” that option-ally increases the maximum speed of IEEE 802.11b wirelesslinks from 11 to 22 Mbps. When this turbo feature is appliedto IEEE 802.11a wireless links, the maximum speed isincreased from 54 to 72 Mbps.
  20. 20. 4 ACCESS POINTSFigure A-3 An example of a consumer AP is this 5-GHz wireless accesspoint (WAP54A) from Linksys, which features antenna with a range of upto 328 feet indoors. Enterprise-level APs provide more management features,allowing LAN administrators to remotely set up and configuremultiple APs and clients from a central location. For monitor-ing and managing an entire wireless LAN infrastructure con-sisting of hundreds or even thousands of access points,however, a dedicated management system is usually required.Such systems automatically discover every AP on the networkand provide real-time monitoring of an entire wireless networkspread out over multiple facilities and subnets. These manage-ment systems support the Simple Network ManagementProtocol (SNMP) and can be tied into higher-level managementplatforms such as Hewlett-Packard’s OpenView.
  21. 21. ACCESS POINTS 5 Among the capabilities of these wireless managers is sup-port of remote reboot, group configuration, or group softwareuploads for all the wireless infrastructure devices on the net-work. In addition, the LAN administrator can see how manyclient devices are connected to each access point, monitorthose connections to measure link quality, and monitor allthe access points for performance. Some enterprise APs provide dual-band wireless connec-tions to support both IEEE 802.11a and 802.11b client usersat the same time. This is accomplished by equipping the APwith two plug-in radio cards—one that supports the 2.4-GHzfrequency specified by the IEEE 802.11b Standard and onethat supports the 5-GHz frequency specified by the IEEE802.11a Standard. The choice of a dual-band AP provides organizations witha migration path to the higher data transfer speeds availablewith IEEE 802.11a while continuing to support their existinginvestment in IEEE 802.11b infrastructure. Depending onmanufacturer, these dual-band APs are modular so that theycan be upgraded to support future IEEE 802.11 technologiesas they become available, which further protects an organi-zation’s investment in wireless infrastructure.SummaryAccess points are the devices that connect wireless clientdevices to the wired network. They are available in con-sumer and commercial versions, with the latter generallycosting more because of more extensive management capa-bilities and troubleshooting features. They may have moresecurity features as well and support both the 2.4- and 5-GHz frequency bands with separate radio modules that pluginto the same unit.See also Bluetooth Wired Equivalent Privacy Wireless Fidelity
  22. 22. 6 ADVANCED MOBILE PHONE SERVICE Wireless LANs Wireless SecurityADVANCED MOBILE PHONE SERVICEADVANCED SERVICEBefore the age of digital services, the predominant technologyfor analog cellular phone services in North America adheredto a set of standards for Advanced Mobile Phone Service(AMPS). Originally, AMPS operated in the 800-MHz fre-quency band using 30-kHz-wide channels. A variant of AMPS,known as Narrowband AMPS (NAMPS), uses 10-kHz-widechannels and consequently has triple the capacity of AMPS.Although AMPS or a variation of AMPS is still around—chances are that your cellular phone allows you to switchbetween analog and digital mode—its use is rapidly decliningin the face of more sophisticated digital cellular standards. The mobile telephone service that preceded AMPS wasknown as Improved Mobile Telephone Service (IMTS), whichoperated in several frequency ranges: 35 to 44 MHz, 152 to158 MHz, and 454 to 512 MHz. But IMTS suffered from callsetup delay, poor transmission, and limited frequency reuse.AMPS overcame the limitations of IMTS and set the stagefor the explosive growth of cellular service, which continuestoday worldwide. Interestingly, Pacific Bell finally droppedIMTS in 1995. Proposed by AT&T in 1971, AMPS is still the standard foranalog cellular networks. It was tested in 1978, and in theearly 1980s cellular systems based on the standards wereinstalled throughout North America. Although AMPS wasnot the first system for wireless telephony, the existence of asingle set of standards enabled the United States to domi-nate analog cellular throughout the 1980s. Today, Europedominates cellular primarily because it is a lower-cost alter-native to conventional telephone service. Analog cellular is delivered from a system of cellular hubsand base stations with associated radio towers. A mobile
  23. 23. ADVANCED MOBILE PHONE SERVICE 7telecommunications switching office (MTSO) authenticateswireless customers before they make calls, switches callsbetween cells as mobile phone users travel across cell bound-aries, and places calls from land-based telephones to wire-less customers. AMPS uses a technique called “frequency reuse” to greatlyincrease the number of customers that can be served at thesame time. Low-powered mobile phones and radio equipmentat each cell site permit the same radio frequencies to bereused in different cells, multiplying calling capacity withoutcreating interference. This spectrum-efficient method con-trasts sharply with earlier mobile systems that used a high-powered, centrally located transmitter to communicate withhigh-powered mobile equipment installed in vehicles over asmall number of frequencies. Once a channel was occupiedwith a call, its frequency could not reused over a wide area. Despite the success of AMPS, this method of transmissionhas its limitations. Analog signals can be intercepted easilyand suffer signal degradation from numerous sources, suchas terrain, weather, and traffic volume. Analog systems alsocould not handle the transmission of data very well. A digi-tal version of AMPS—referred to as DAMPS—solves manyof these problems while providing increased capacity and agreater range of services. Both AMPS and DAMPS operatein the 800-MHz band and can coexist with each other.DAMPS is implemented with Time Division Multiple Access(TDMA) as the underlying technology, which provides 10 to15 times more channel capacity than AMPS and allows theintroduction of new feature-rich services such as data com-munications, voice mail, call waiting, call diversion, voiceencryption, and calling-line identification. A digital control channel available with DAMPS supportssuch advanced features as a sleep mode, which increases bat-tery life on newer cellular phones by as much as 10 times overthe current battery capabilities of analog phones. DAMPSalso can be implemented with Code Division Multiple Access(CDMA) technology to increase channel capacity by as much
  24. 24. 8 AIR-GROUND RADIOTELEPHONE SERVICEas 20 times and provide a comparable range of services andfeatures. Unlike TDMA, which can be added onto existingAMPS infrastructure, CDMA requires an entirely new net-work infrastructure. DAMPS also allows operators to build overlay networksusing small micro- and picocells, boosting network capacitystill further in high-traffic areas and providing residentialand business in-building coverage. Advanced software in thenetworks’ exchanges continuously monitors call quality andmakes adjustments, such as handing calls over to differentcells or radio channels, when necessary. The network man-agement system provides an early warning to the networkoperator if the quality of service is deteriorating so that stepscan be taken to head off serious problems. Graphical dis-plays of network configuration and performance statisticshelp ensure maximum service quality for subscribers.SummaryIn 1983, AMPS was approved by the Federal CommunicationsCommission (FCC) and first used in Chicago. In order toencourage competition and keep prices low, the U.S. govern-ment required the presence of two carriers in every market,known as A and B carriers. One of the carriers was normallythe Local Exchange Carrier (LEC); in other words, the localphone company.See also Cellular Data Communications Cellular Voice CommunicationsAIR-GROUND RADIOTELEPHONE SERVICE SERVICEWith the Air-Ground Radiotelephone Service, a commercialmobile radio service (CMRS) provider offers two-way voice,
  25. 25. AIR-GROUND RADIOTELEPHONE SERVICE 9fax, and data service for hire to subscribers in aircraft—inflight or on the ground. Service providers must apply for anFCC license for each and every tower/base site. There aretwo versions of this service: one for general aviation and onefor commercial aviation.General Aviation Air-Ground ServiceAir-Ground Radiotelephone Service has been available togeneral aviation for more than 30 years. General AviationAir-Ground systems may operate in the 454.675- to 454.975-MHz and 459.675- to 459.975-MHz bands to provide serviceto private aircraft, specifically, small single-engine craft andcorporate jets. The service is implemented through general aviationair-ground stations, which comprise a network of indepen-dently licensed stations. These stations employ a stan-dardized duplex analog technology called “Air-GroundRadiotelephone Automated Service” (AGRAS) to providetelephone service to subscribers flying over the UnitedStates or Canada. Because there are only 12 channelsavailable for this service, it is not available to passengerson commercial airline flights.Commercial Aviation Air-Ground SystemsCommercial Aviation Air-Ground Systems may operate on10 channel blocks in the 849- to 851-MHz and 894- to 896-MHz bands. These nationwide systems employ various ana-log or digital wireless technologies to provide telephoneservice to passengers flying in commercial aircraft over theUnited States, Canada, and Mexico. Some systems havesatellite-calling capability as well, where the call is sent toan earth station instead of the base station. Passengers use credit cards or prearranged accounts tomake telephone calls from bulkhead-mounted telephonesor, in larger jets, from seatback-mounted telephones. This
  26. 26. 10 AIR-GROUND RADIOTELEPHONE SERVICEservice was available from one company on an experimentalbasis during the 1980s and began regular competitive oper-ations in the early 1990s. There are currently three operat-ing systems, one of which is GTE Airfone, a subsidiary ofVerizon Communications. When an Airfone call is placed over North America, infor-mation is sent from the phone handset to a receiver in theplane’s belly and then down to one of the 135 strategicallyplaced ground radio base stations. From there, it is sent toone of three main ground switching stations and then overto the public telephone network to the receiving party’s loca-tion. When an Airfone call is placed over water, informationis sent first to an orbiting satellite. From there, the calltransmission path is similar to the North American system,except that calls are sent to a satellite earth station insteadof a radio base station. Calls can be placed to any domesticor international location. To receive calls aboard aircraft, the passenger musthave an activation number. In the case of Airfone, an acti-vation number can be obtained by dialing 0 toll-freeonboard or 1-800-AIRFONE from the ground. For eachflight segment, the activation number will be the same.However, the passenger must activate the phone for eachflight segment and include his or her seat number. Theperson placing the call from the ground dials 1-800-AIR-FONE and follows the voice prompts to enter the passen-ger’s activation number. The passenger is billed for the callon a calling card or credit card but gets to choose whetheror not to accept the calls. The following steps are involved in receiving a call:G The phone will ring on the plane, and the screen will indi- cate a call for the seat location.G The passenger enters a personal identification number (PIN) to ensure that no one else can answer the call.G The phone number of the calling party will be displayed on the screen.
  27. 27. AIR-GROUND RADIOTELEPHONE SERVICE 11G If the call is accepted, the passenger is prompted to slide a calling card or credit card to pay for the call.G Once the call has been accepted, the passenger is auto- matically connected to the party on the ground.G If the passenger chooses not to accept the call, he or she follows the screen prompts, and no billing will occur. Air-to-ground calls are very expensive. The cost to placedomestic calls using GTE’s Airfone Service, for example, is$2.99 to connect and $3.28 per minute or partial minute,plus applicable tax. By comparison, AT&T’s InflightCalling costs $2.99 to connect plus $2.99 per minute.These rates apply to all data/fax and voice calls. Evencalls to 800 and 888 numbers—which are normally toll-free on the ground—are charged at the same rate as regu-lar Airfone and Inflight calls. No billing ever occurs for theground party. The charges for international calls arehigher; both AT&T and GTE charge $5.00 to connect and$5.00 per minute. GTE offers satellite service for use overthe ocean and worldwide at $10.00 to connect and $10.00per minute, but the service is available only on UnitedAirlines.SummaryFCC rules specifically prohibit the use of cellular trans-mitters on aircraft, except for aircraft on the ground. Thisprohibition was not done to protect the aircraft’s avionicssystems from interference from the cellular transmitter.Rather, this prohibition was made to protect the cellularservice on the ground from interference. As the altitude ofa cellular handheld transmitter increases, its range alsoincreases and, consequently, its coverage area. At highaltitudes, such as would be achieved from an in-flight air-craft, the hand-held unit places its signal over several cel-lular base stations, preventing other cellular users withinrange of those base stations from using the same frequency.
  28. 28. 12 AMATEUR RADIO SERVICEThis would increase the number of blocked or dropped cel-lular calls.See also Cellular Data Communications Cellular Voice CommunicationsAMATEUR RADIO SERVICEAMATEUR SERVICEAmateur Radio Service is defined by the FCC as “A radiocommunication service for the purpose of self-training, inter-communication, and technical investigations carried out byamateurs; that is, duly authorized persons interested inradio technique solely with a personal aim and without pecu-niary interest.”1 Amateur radio stations are licensed by the FCC and mayengage in domestic and international communications—both two-way and one-way. Applications for new licenses orfor a change in operator class are filed through a volunteerexaminer-coordinator (VEC). Operators can use their sta-tion equipment as soon as they see that information abouttheir amateur operator/primary station license grantappears on the amateur service database. New operatorsdo not need to have the license document in their posses-sion to commence operation of an amateur radio station. Since amateur stations must share the air waves, eachstation licensee and each control operator must cooperate inselecting transmitting channels and in making the mosteffective use of the amateur service frequencies. A specifictransmitting channel is not assigned for the exclusive use ofany amateur station.1There are two exceptions to this rule. A person may accept compensation when in ateaching position and the amateur station is used as a part of classroom instruction atan educational institution. The other exception is when the control operator of a clubstation is transmitting telegraphy practice or information bulletins.
  29. 29. AMATEUR RADIO SERVICE 13Types of CommunicationsWith regard to two-way communications, amateur stationsare authorized to exchange messages with other stations inthe amateur service, except those in any country whoseadministration has given notice that it objects to such com-munications.2 In addition, transmissions to a different coun-try must be made in plain language. Communication islimited to messages of a technical nature relating to testsand to remarks of a personal nature for which, by reason oftheir unimportance, use of public telecommunications ser-vices is not justified. Amateur radio stations also may engage in one-way com-munications. For example, they are authorized to transmitauxiliary, beacon, and distress signals. Specifically, an ama-teur station may transmit the following types of one-waycommunications:G Brief transmissions necessary to make adjustments to the stationG Brief transmissions necessary for establishing two-way communications with other stationsG Transmissions necessary to provide emergency communi- cationsG Transmissions necessary for learning or improving profi- ciency in the use of international Morse codeG Transmissions necessary to disseminate an information bulletin of interest to other amateur radio operatorsG TelemetryProhibited CommunicationsAlthough the FCC does not provide a list of communicationsthat are suitable or unsuitable for the amateur radio service,2As of mid-2002, no administration in another country had given notice that theyobject to communications between the amateur radio stations.
  30. 30. 14 AMATEUR RADIO SERVICEthere are several types of amateur-operator communicationsthat are specifically prohibited, includingG Transmissions performed for compensationG Transmissions done for the commercial benefit of the sta- tion control operatorsG Transmissions done for the commercial benefit of the sta- tion control operator’s employerG Transmissions intended to facilitate a criminal actG Transmissions that include codes or ciphers intended to obscure the meaning of the messageG Transmissions that include obscene or indecent words or languageG Transmissions that contain false or deceptive messages, signals, or identificationG Transmissions on a regular basis that could reasonably be furnished alternatively through other radio services Broadcasting information intended for the general public isalso prohibited. Amateur stations may not engage in any formof broadcasting or in any activity related to program produc-tion or newsgathering for broadcasting purposes. The oneexception is when communications directly related to theimmediate safety of human life or the protection of propertymay be provided by amateur stations to broadcasters for dis-semination to the public where no other means of communica-tion is reasonably available before or at the time of the event. Amateur stations are not afforded privacy protection.This means that the content of the communications by ama-teur stations may be intercepted by other parties anddivulged, published, or used for another purpose.SummaryIn August 1999, the FCC’s Wireless TelecommunicationsBureau (WTB) began the transition to the Universal Licensing
  31. 31. AMATEUR RADIO SERVICE 15System (ULS) for all application and licensing activity in theAmateur Radio Services. As of February 2000, amateurlicensees were required to file using ULS forms, which meansthat applications using Forms 610 and 610V are no longeraccepted by the WTB.3 The ULS is an interactive licensingdatabase developed by the WTB to consolidate and replace 11existing licensing systems used to process applications andgrant licenses in wireless services. ULS provides numerousbenefits, including fast and easy electronic filing, improveddata accuracy through automated checking of applications,and enhanced electronic access to licensing information.See also Citizens Band Radio Service Telegraphy Telemetry3 For applications that do not need to be filed by a volunteer-examiner coordinator(VEC), such as renewals and administrative updates. Amateur Service licensees maystill file FCC Form 605 electronically (interactively) or manually, despite the ULSrequirement for other filings.
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  33. 33. BBASIC EXCHANGE TELEPHONE RADIOSERVICESERVICEDeveloped in the mid-1980s, Basic Exchange Telephone RadioService (BETRS) is a fixed radio service that uses a multi-plexed digital radio link as the last segment of the local loopto provide wireless telephone service to subscribers in remoteareas where it would be impractical to provide wireline tele-phone service. The wireless link allows up to four subscribersto use a single radio channel pair simultaneously withoutinterfering with one another. Licensed by the Federal Communications Commission(FCC) under the Rural Radiotelephone Service, BETRS maybe licensed only to state-certified carriers in the area wherethe service is provided and is considered a part of the PublicSwitched Telephone Network (PSTN) by state regulators. This service operates in the paired 152/158- and 454/459-MHz bands and on 10 channel blocks in the 816- to 820-MHzand 861- to 865-MHz bands. These channels are also allo-cated for paging services. Since BETRS primarily servesrural areas in the western part of the United States, it typi-cally does not conflict geographically with paging services.When there is a conflict, the FCC provides a remedy. 17 Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  34. 34. 18 BLUETOOTH Rural Radiotelephone Service and BETRS providersobtain site licenses and operate facilities on a secondarybasis. This means that if any geographic area licensee sub-sequently notifies the Rural Radiotelephone Service orBETRS licensee that a facility must be shut down because itmay cause interference to the paging licensee’s existing orplanned facilities, the Rural Radiotelephone Service orBETRS licensee must discontinue use of the particular chan-nel at that site no later than 6 months after such notice.SummaryBETRS primarily serves rural, mountainous, and sparselypopulated areas that might not otherwise receive basic tele-phone service. Although the industry has raised concernsthat auctioning spectrum for BETRS would have the effectof raising the cost of the service, which could deprive theseareas of basic telephone service, the FCC does not distin-guish BETRS from other services that use radio spectrum toprovide commercial communication services.See also Rural Radiotelephone ServiceBLUETOOTHBluetooth is an omnidirectional wireless technology that pro-vides limited-range voice and data transmission over the unli-censed 2.4-GHz frequency band, allowing connections with awide variety of fixed and portable devices that normally wouldhave to be cabled together. Up to eight devices—one masterand seven slaves—can communicate with one another in a so-called piconet at distances of up to 30 feet. Table B-1 summa-rizes the performance characteristics of Bluetooth productsthat operate at 1 Mbps in the 2.4-GHz range.
  35. 35. BLUETOOTH 19ApplicationsAmong the many things users can do with Bluetooth is swapdata and synchronize files merely by having the devicescome within range of one another. Images captured with adigital camera, for example, can be dropped off at a personalcomputer (PC) for editing or a color printer for output onphoto-quality paper—all without having to connect cables,load files, open applications, or click buttons. The technology is a combination of circuit switching andpacket switching, making it suitable for voice as well asdata. Instead of fumbling with a cell phone while driving, forexample, the user can wear a lightweight headset to answera call and engage in a conversation even if the phone istucked away in a briefcase or purse. While useful in minimizing the need for cables, wirelesslocal area networks (LANs) are not intended for intercon-necting the range of mobile devices people carry aroundeveryday between home and office. For this, Bluetooth isneeded. And in the office, a Bluetooth portable device can beTABLE B-1 Performance Characteristics of Bluetooth ProductsFeature/Function PerformanceConnection type Spread spectrum (frequency hopping)Spectrum 2.4-GHz ISM (industrial, scientific, and medical) bandTransmission power 1 milliwatt (mW)Aggregate data rate 1 Mbps using frequency hoppingRange Up to 30 feet (9 meters)Supported stations Up to eight devices per piconetVoice channels Up to three synchronous channelsData security For authentication, a 128-bit key; for encryption, the key size is configurable between 8 and 128 bitsAddressing Each device has a 48-bit Media Access Control (MAC) address that is used to establish a connection with another device
  36. 36. 20 BLUETOOTHin motion while connected to the LAN access point as long asthe user stays within the 30-foot range. Bluetooth can be combined with other technologies tooffer wholly new capabilities, such as automatically lower-ing the ring volume of cell phones or shutting them off asusers enter quiet zones such as churches, restaurants, the-aters, and classrooms. On leaving the quiet zone, the cellphones are returned to their original settings.TopologyThe devices within a piconet play one of two roles: that ofmaster or slave. The master is the device in a piconet whoseclock and hopping sequence are used to synchronize all otherdevices (i.e., slaves) in the piconet. The unit that carries outthe paging procedure and establishes a connection is bydefault the master of the connection. The slaves are theunits within a piconet that are synchronized to the mastervia its clock and hopping sequence. The Bluetooth topology is best described as a multiple-piconet structure. Since Bluetooth supports both point-to-point and point-to-multipoint connections, several piconetscan be established and linked together in a topology called a“scatternet” whenever the need arises (Figure B-1). Piconets are uncoordinated, with frequency hoppingoccurring independently. Several piconets can be establishedand linked together ad hoc, where each piconet is identifiedby a different frequency-hopping sequence. All users partic-ipating on the same piconet are synchronized to this hoppingsequence. Although synchronization of different piconets isnot permitted in the unlicensed ISM band, Bluetooth unitsmay participate in different piconets through Time DivisionMultiplexing (TDM). This enables a unit to sequentially par-ticipate in different piconets by being active in only onepiconet at a time. With its service discovery protocol, Bluetooth enables amuch broader vision of networking, including the creation of
  37. 37. BLUETOOTH 21 Master Slaves Master Master Master Slave Master Slaves Slave Slaves SlaveSingle Slave Multi-Slave Scatternet Piconet PiconetFigure B-1 Possible topologies of networked Bluetooth devices, whereeach is either a master or slave.personal area networks, where all the devices in a person’slife can communicate and work together. Technical safe-guards ensure that a cluster of Bluetooth devices in publicplaces, such as an airport lounge or train terminal, wouldnot suddenly start talking to one another.TechnologyTwo types of links have been defined for Bluetooth in sup-port of voice and data applications: an asynchronous connec-tionless (ACL) link and a synchronous connection-oriented(SCO) link. ACL links support data traffic on a best-effortbasis. The information carried can be user data or controldata. SCO links support real-time voice and multimediatraffic using reserved bandwidth. Both data and voice arecarried in the form of packets, and Bluetooth devices cansupport active ACL and SCO links at the same time. ACL links support symmetric or asymmetric packet-switched point-to-multipoint connections, which are typically
  38. 38. 22 BLUETOOTHused for data. For symmetric connections, the maximum datarate is 433.9 kbps in both directions, send and receive. Forasymmetric connections, the maximum data rate is 723.2kbps in one direction and 57.6 kbps in the reverse direction.If errors are detected at the receiving device, a notification issent in the header of the return packet so that only lost or cor-rupt packets need to be retransmitted. SCO links provide symmetric circuit-switched point-to-point connections, which are typically used for voice. Threesynchronous channels of 64 kbps each are available for voice.The channels are derived through the use of either PulseCode Modulation (PCM) or Continuous Variable Slope Delta(CVSD) Modulation. PCM is the standard for encodingspeech in analog form into the digital format of ones andzeros. CVSD is another standard for analog-to-digital encod-ing but offers more immunity to interference and thereforeis better suited than PCM for voice communication over awireless link. Bluetooth supports both PCM and CVSD; theappropriate voice-coding scheme is selected after negotia-tions between the link managers of each Bluetooth devicebefore the call takes place. Voice and data are sent as packets. Communication ishandled with Time Division Duplexing (TDD), which dividesthe channel into time slots, each 625 microseconds (µs) inlength. The time slots are numbered according to the clock ofthe piconet master. In the time slots, master and slave cantransmit packets. In the TDD scheme, master and slavealternatively transmit (Figure B-2). The master starts itstransmission in even-numbered time slots only, and theslave starts its transmission in odd-numbered time slotsonly. The start of the packet is aligned with the slot start.Packets transmitted by the master or the slave may extendover as many as five time slots. With TDD, bandwidth can be allocated on an as-neededbasis, changing the makeup of the traffic flow as demandwarrants. For example, if the user wants to download a largedata file, as much bandwidth as is needed will be allocated
  39. 39. BLUETOOTH 23 Channel Time Slot 0 Time Slot 1 Time Slot 2 Master Send Receive Send Slave 625 µsFigure B-2 With the TDD scheme used in Bluetooth, packets are sentover time slots of 625 microseconds (µs) in length between the master andslave units within a piconet.to the transfer. Then, at the next moment, if a file is beinguploaded, that same amount of bandwidth can be allocatedto that transfer. No matter what the application—voice or data—makingconnections between Bluetooth devices is as easy as power-ing them up. In fact, one advantage of Bluetooth is that itdoes not need to be set up—it is always on, running in thebackground, and looking for other devices that it can com-municate with. When Bluetooth devices come within range of oneanother, they engage in a service discovery procedure, whichentails the exchange of messages to become aware of eachother’s service and feature capabilities. Having locatedavailable services within the vicinity, the user may selectfrom any of them. After that, a connection between two ormore Bluetooth devices can be established. The radio link itself is very robust, using frequency-hopping spread-spectrum technology to overcome interfer-ence and fading. Spread spectrum is a digital coding tech-nique in which the signal is taken apart or “spread” so that
  40. 40. 24 BLUETOOTHit sounds more like noise as it is sent through the air. Withthe addition of frequency hopping—having the signals skipfrom one frequency to another—wireless transmissions aremade even more secure. Bluetooth specifies a rate of 1600hops per second among 79 frequencies. Since only the senderand receiver know the hopping sequence for coding anddecoding the signal, eavesdropping is virtually impossible.For enhanced security, Bluetooth also supports deviceauthentication and encryption. Other frequency-hopping transmitters in the vicinity willbe using different hopping patterns and much slower hoprates than Bluetooth devices. Although the chance ofBluetooth devices interfering with non-Bluetooth devicesthat share the same 2.4-GHz band is minimal, should non-Bluetooth transmitters and Bluetooth transmitters coinci-dentally attempt to use the same frequency at the samemoment, the data packets transmitted by one or both deviceswill become garbled in the collision, and a retransmission ofthe affected data packets will be required. A new data packetwill be sent again on the next hopping cycle of each trans-mitter. Voice packets, because of their sensitivity to delay,are never retransmitted.Points of ConvergenceIn some ways, Bluetooth competes with infrared, and inother ways, the two technologies are complementary. Withboth infrared and Bluetooth, data exchange is considered tobe a fundamental function. Data exchange can be as simpleas transferring business card information from a mobilephone to a palmtop or as sophisticated as synchronizing per-sonal information between a palmtop and desktop PC. Infact, both technologies can support many of the same appli-cations, raising the question: Why would users need bothtechnologies? The answer lies in the fact that each technology has itsadvantages and disadvantages. The very scenarios that leave
  41. 41. BLUETOOTH 25infrared falling short are the ones where Bluetooth excels,and vice versa. Take the electronic exchange of business cardinformation between two devices. This application usuallywill take place in a conference room or exhibit floor where anumber of other devices may be attempting to do the samething. This is the situation where infrared excels. The short-range and narrow angle of infrared—30 degrees or less—allow each user to aim his or her device at the intendedrecipient with point-and-shoot ease. Close proximity toanother person is natural in a business card exchange situa-tion, as is pointing one device at another. The limited rangeand angle of infrared allow other users to perform a similaractivity with ample security and no interference. In the same situation, a Bluetooth device would not per-form as well as an infrared device. With its omnidirectionalcapability, the Bluetooth device must first discover theintended recipient. The user cannot simply point at theintended recipient—a Bluetooth device must perform a dis-covery operation that probably will reveal several otherBluetooth devices within range, so close proximity offers noadvantage here. The user will be forced to select from a listof discovered devices and apply a security mechanism to pre-vent unauthorized access. All this makes the use ofBluetooth for business card exchange an awkward and need-lessly time-consuming process. However, in other data-exchange situations, Bluetoothmight be the preferred choice. Bluetooth’s ability to pene-trate solid objects and its ability to communicate with otherdevices in a piconet allow for data-exchange opportunitiesthat are very difficult or impossible with infrared. For exam-ple, Bluetooth allows a user to synchronize a mobile phonewith a notebook computer without taking the phone out of ajacket pocket or purse. This would allow the user to type anew address at the computer and move it to the mobilephone’s directory without unpacking the phone and settingup a cable connection between the two devices. The omnidi-rectional capability of Bluetooth allows synchronization to
  42. 42. 26 BLUETOOTHoccur instantly, assuming that the phone and computer arewithin 30 feet of each other. Using Bluetooth for synchronization does not require thatthe phone remain in a fixed location. If a phone is carriedabout in a briefcase, the synchronization can occur while theuser moves around. This is not possible with infrared becausethe signal is not able to penetrate solid objects, and thedevices must be within a few feet of each other. Furthermore,the use of infrared requires that both devices remain station-ary while the synchronization occurs. When it comes to data transfers, infrared does offer a bigspeed advantage over Bluetooth. While Bluetooth moves databetween devices at an aggregate rate of 1 Mbps, infraredoffers 4 Mbps of data throughput. A higher-speed version ofinfrared is now available that can transmit data betweendevices at up to 16 Mbps—a four times improvement over theprevious version. The higher speed is achieved with the VeryFast Infrared (VFIR) Protocol, which is designed to addressthe new demands of transferring large image files betweendigital cameras, scanners, and PCs. Even when Bluetooth isenhanced for higher data rates in the future, infrared is likelyto maintain its speed advantage for many years to come. Bluetooth complements infrared’s point-and-shoot ease ofuse with omnidirectional signaling, longer-distance commu-nications, and capacity to penetrate walls. For some users,having both Bluetooth and infrared will provide the optimalshort-range wireless solution. For others, the choice ofadding Bluetooth or infrared will be based on the applica-tions and intended usage.SummaryCommunicator platforms of the future will combine a numberof technologies and features in one device, including mobileInternet browsing, messaging, imaging, location-based appli-cations and services, mobile telephony, personal informationmanagement, and enterprise applications. Bluetooth will be a
  43. 43. BRIDGES 27key component of these platforms. Since Bluetooth radiotransceivers operate in the globally available ISM (indus-trial, scientific, and medical) radio band of 2.4 GHz, productsdo not require an operator license from a regulatory agency,such as the FCC in the United States. The use of a generallyavailable frequency band means that Bluetooth-enableddevices can be used virtually anywhere in the world and linkup with one another for ad hoc networking when they comewithin range.See also Infrared Networking Spread Spectrum RadioBRIDGESBridges are used to extend or interconnect LAN segments,whether the segments consist of wired or wireless links. Atone level, they are used to create an extended network thatgreatly expands the number of devices and services avail-able to each user. At another level, bridges can be used forsegmenting LANs into smaller subnets to improve perfor-mance, control access, and facilitate fault isolation and test-ing without impacting the overall user population. The bridge does this by monitoring all traffic on the sub-nets that it links. It reads both the source and destinationaddresses of all the packets sent through it. If the bridgeencounters a source address that is not already contained inits address table, it assumes that a new device has beenadded to the local network. The bridge then adds the newaddress to its table. In examining all packets for their source and destinationaddresses, bridges build a table containing all local addresses.The table is updated as new packets are encountered and asaddresses that have not been used for a specified period of time
  44. 44. 28 BRIDGESare deleted. This self-learning capability permits bridges tokeep up with changes on the network without requiring thattheir tables be updated manually. The bridge isolates traffic by examining the destinationaddress of each packet. If the destination address matchesany of the source addresses in its table, the packet is notallowed to pass over the bridge because the traffic is local.If the destination address does not match any of the sourceaddresses in the table, the packet is discarded onto anadjacent network. This filtering process is repeated ateach bridge on the internetwork until the packet eventu-ally reaches its destination. Not only does this processprevent unnecessary traffic from leaking onto the inter-network, it acts as a simple security mechanism that canscreen unauthorized packets from accessing various corpo-rate resources. Bridges also can be used to interconnect LANs that usedifferent media, such as twisted-pair, coaxial, and fiberop-tic cabling and various types of wireless links. In officeenvironments that use wireless communications technolo-gies such as spread spectrum and infrared, bridges canfunction as an access point to wired LANs (Figure B-3). Onthe widea area network (WAN), bridges even switch trafficto a secondary port if the primary port fails. For example,a full-time wireless bridging system can establish amodem connection on the public network if the primarywire or wireless link is lost because of environmentalinterference. In reference to the Open Systems Interconnection (OSI)model, a bridge operates at Layer 2; specifically, it oper-ates at the Media Access Control (MAC) sublayer of theData Link Layer. It routes by means of the Logical LinkControl (LLC), the upper sublayer of the Data Link Layer(Figure B-4). Because the bridge connects LANs at a relatively lowlevel, throughput often exceeds 30,000 packets per second
  45. 45. BRIDGES 29Figure B-3 For the home or small office network, the InstantWireless Ethernet Bridge from Linksys extends wireless connec-tivity to any Ethernet-ready network device, such as a printer,scanner, or desktop or notebook PC.(pps). Multiprotocol routers and gateways, which provideLAN interconnection over the WAN, operate at higher levelsof the OSI model and provide more functionality. In per-forming more protocol conversions and delivering more func-tionality, routers and gateways are generally moreprocessing-intensive and, consequently, slower than bridges.
  46. 46. 30 BRIDGES Source Station Destination Station7 Application Application 76 Presentation Presentation 65 Session Session 54 Transport Transport 4 Bridge3 Network Network 3 Data Link Data Link2 Data Link (MAC/LCC) (MAC/LCC) Data Link 21 Physical Physical Physical Physical 1 Ethernet EthernetFigure B-4 Bridge functionality in reference to the OSI modelSee also Access Points Repeaters Routers
  47. 47. CCELL SITESA cellular system operates by dividing a large geographic ser-vice area into cells (Figure C-1) and assigning the same fre-quencies to multiple, nonadjacent cells. This is known in theindustry as “frequency reuse.” As a subscriber travels acrossthe service area, the call is transferred (handed off) from onecell to another without noticeable interruption. All the base sta-tions in a cellular system, including radio towers, are connectedto a mobile telephone switching office (MTSO) by landline ormicrowave links. The MTSO controls the switching betweenthe Public Switched Telephone Network (PSTN) and the cellsite for all wireline-to-mobile and mobile-to-wireline calls.Site PlanningThere is a huge investment at stake when determining thelocation of a cell site. The radio tower alone can cost from$250,000 to $1 million. Thus, before a cell site is installed, anumber of studies are performed to justify the cost and calcu-late the return on investment (ROI). A demographics study, forexample, helps forecast the potential subscriber base in thearea planned for the cell site. The study begins with the total 31 Copyright 2003 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  48. 48. 32 CELL SITES 3 2 1 4 1 2 3Figure C-1 In a cellular network, the signal cover-age of each tower is limited so that the same fre-quencies can be assigned to multiple nonadjacentcells. This increases the total call-handling capacityof the network while conserving spectrum.population, broken down by sex, age, race, types of households,occupancy rates, and income levels. Much of this informationis gleaned from data compiled by the U.S. Census Bureau. By generating a topography map, engineers are able todetermine if there will be any obvious interference issues. Thegoal is to discover problems that would impair the perfor-mance of the wireless cell site solution or wireless link.Sometimes a 50-foot portable crank-up tower is used to createa temporary cell site. Together with vehicles containing bothaccess points and subscriber units, tests are run to find outwhat may interfere with the signal and demonstrate a real-time cell site coverage area. After determining any interference issues and the beststrategic location for the cell site, a full site survey is done to
  49. 49. CELL SITES 33establish the final plans for cell site deployment. Thisincludes having all the information about the types of mountsneeded as well as having potential interference-filteringmeasures defined. Certified network engineers then deter-mine the best base station configuration and orientation. Ifno problems are encountered, a tower can be up and runningwithin 6 weeks.RegulationThe Telecommunications Act of 1996 specifically leaves inplace the authority that local zoning authorities have over theplacement of cell towers. It does prohibit the denial of facili-ties siting based on radio frequency (RF) emissions if thelicensee has complied with the Federal CommunicationsCommission’s (FCC’s) regulations concerning RF emissions. Italso requires that denials be based on a reasoned approachand prohibits discrimination and outright bans on construc-tion, placement, and modification of wireless facilities. The FCC mandates that service providers build out theirsystems so that adequate service is provided to the public. Inaddition, all antenna structures used for communicationsmust be approved by the FCC, which determines if there isa reasonable possibility that the structure may constitute amenace to air navigation. The tower height and its proxim-ity to an airport or flight path will be considered when mak-ing this determination. If such a determination is made, theFCC will specify appropriate painting and lighting require-ments. Thus the FCC does not mandate where towers mustbe placed, but it may prohibit the placement of a tower in aparticular location without adequate lighting and marking.SummaryLow-powered transmitters are an inherent characteristic ofcellular radio and broadband personal communication ser-vices (PCS). As these systems mature and more subscribers
  50. 50. 34 CELLULAR DATA COMMUNICATIONSare added, the effective radiated power of the cell site trans-mitters is reduced so that frequencies can be reused at closerintervals, thereby increasing subscriber capacity. There aremore than 50,000 cell sites operating within the UnitedStates and its possessions and territories. Therefore, due tothe nature of frequency reuse and the consumer demand forservices, cellular and PCS providers must build numerousbase sites. The sheer number of towers has caused munici-palities to impose new requirements on service providers,such as requiring them to disguise new towers to look liketrees, which can add $150,000 to the cost of a tower.See also Cellular Data Communications Cellular Voice Communications Mobile Telephone Switching Office Personal Communications ServicesCELLULAR DATA COMMUNICATIONS DAT COMMUNICATIONSOne of the oldest services for sending data over a cellularcommunications network is known as “Cellular DigitalPacket Data” (CDPD), which provides a way of passingInternet Protocol (IP) data packets over analog cellular voicenetworks at speeds of up to 19.2 kbps. Although CDPDemploys digital modulation and signal processing tech-niques, the underlying service is still analog. The mediumused to transport data consists of the idle radio channels typ-ically used for Advanced Mobile Phone System (AMPS) cel-lular service. Channel hopping automatically searches out idle channeltimes between cellular voice calls. Packets of data selectavailable cellular channels and go out in short bursts withoutinterfering with voice communications. Alternatively, cellu-lar carriers also may dedicate voice channels for CDPD traf-
  51. 51. CELLULAR DATA COMMUNICATIONS 35fic to meet high traffic demand. This situation is common indense urban environments where cellular traffic is heaviest. Once the user logs onto the network, the connection staysin place to send or receive data. In accordance with the IP,the data are packaged into discrete packets of informationfor transmission over the CDPD network, which consists ofrouters and digital radios installed in current cell sites. Inaddition to addressing information, each IP packet includesinformation that allows the data to be reassembled in theproper order via the Transmission Control Protocol (TCP) atthe receiving end. The transmissions are encrypted over theair link for security purposes. Although CDPD piggybacks on top of the cellular voiceinfrastructure, it does not suffer from the 3-kHz limit onvoice transmissions. Instead, it uses the entire 30-kHz RFchannel during idle times between voice calls. Using theentire channel contributes to CDPD’s faster data transmis-sion rate. Forward error correction ensures a high level ofwireless communications accuracy. With encryption andauthentication procedures built into the specification,CDPD offers more robust security than any other nativewireless data transmission method. As with wireline net-works, CDPD users also can customize their own end-to-end security. To take advantage of CDPD, the user must have an inte-grated mobile device that operates as a fully functional cel-lular phone and Internet appliance. For example, theAT&T PocketNet Phone contains both a circuit-switchedcellular modem and a CDPD modem to provide users withfast and convenient access to two-way wireless messagingservices and Internet information. GTE provides a similarservice through its Wireless Data Services. Both compa-nies have negotiated intercarrier agreements that enabletheir customers to enjoy seamless CDPD service in virtu-ally all markets across the country. AT&T’s Wireless IPservice, for example, is available in 3000 cities in theUnited States.
  52. 52. 36 CELLULAR TELEPHONES Among the applications for CDPD are access to theInternet for e-mail and to retrieve certain Web-based content.AT&T PocketNet Phone users, for example, have access totwo-way messaging, airline flight information, financialinformation, show times, restaurant reviews, and door-to-door travel directions. AT&T provides unlimited access to fea-tured sites on the wireless Internet, which means that thereare no per-minute charges for surfing wireless Web sites. Companies also can use CDPD to monitor alarmsremotely, send/receive faxes, verify credit cards, and dispatchvehicles. Although CDPD services might prove too expensivefor heavy database access, the use of intelligent agents cancut costs by minimizing connection time. Intelligent agentsgather requested information and report back only theresults the next time the user logs onto the network.SummaryWireless IP is an appealing method of transporting data overcellular voice networks because it is flexible, fast, widely avail-able, and compatible with a vast installed base of computersand has security features not offered with other wireless dataservices. One caveat: The carrier’s wireless data network isdifferent from its wireless voice network. Therefore, users ofAT&T Digital PocketNet service, for example, will not be ableto access that service everywhere voice calls can be made. It isimportant to look at coverage maps and compare service plansbefore subscribing to this type of service.See also Wireless IPCELLULAR TELEPHONESBell Labs built the first cellular telephone in 1924 (FigureC-2). After decades of development, cellular telephones have
  53. 53. CELLULAR TELEPHONES 37Figure C-2 The first cellular telephone, developed by Bell Labs in 1924.emerged as a “must have” item among mobile professionalsand consumers alike, growing in popularity every year sincethey became commercially available in 1983. Their wide-spread use for both voice and data communications hasresulted from significant progress made in their functional-ity, portability, the availability of network services, and thedeclining cost for equipment and services.System ComponentsThere are several categories of cellular telephone. Mobileunits are mounted in a vehicle. Transportable units can beeasily moved from one vehicle to another. Pocket phones,weighing in at less than 4 ounces, can be conveniently car-ried in a jacket pocket or purse. There are even cellulartelephones that can be worn. Regardless of how they arepackaged, cellular telephones consist of the same basicelements.
  54. 54. 38 CELLULAR TELEPHONESHandset/Keypad The handset and keypad provide the inter-face between the user and the system. This is the only com-ponent of the system with which, under normal operation,the user needs to be concerned. Any basic or enhanced systemfeatures are accessible via the keypad, and once a connectionis established, this component provides similar handset func-tionality to that of any conventional telephone. Until a con-nection is established, however, the operation of the handsetdiffers greatly from that of a conventional telephone. Instead of initiating a call by first obtaining a dial tonefrom the network switching system, the user enters thedialed number into the unit and presses the “Send” functionkey. This process conserves the resources of the cellular sys-tem, since only a limited number of talk paths are availableat any given time. The “Clear” key enables the user to cor-rect misdialed digits. Once the network has processed the call request, the userwill hear conventional call-progress signals such as a busysignal or ringing. From this point on, the handset operatesin the customary manner. To disconnect a call, the “End”function key is pressed on the keypad. The handset containsa small illuminated display that shows dialed digits and pro-vides a navigational aid to other features. The keypadenables storage of numbers for future use and providesaccess to other enhanced features, which may vary accordingto manufacturer.Logic/Control The logic/control functions of the phoneinclude the numeric assignment module (NAM) for pro-grammable assignment of the unit’s telephone number bythe service provider and the electronic serial number of theunit, which is a fixed number unique to each telephone.When a customer signs up for service, the carrier makes arecord of both numbers. When the unit is in service, the cel-lular network interrogates the phone for both of these num-bers in order to validate that the calling/called cellulartelephone is that of an authentic subscriber.
  55. 55. CELLULAR TELEPHONES 39 The logic/control component of the phone also serves tointeract with the cellular network protocols. Among otherthings, these protocols determine what control channel theunit should monitor for paging signals and what voice chan-nels the unit should use for a specific connection. Thelogic/control component is also used to monitor the controlsignals of cell sites so that the phone and network can coor-dinate transitions to adjacent cells as conditions warrant.Transmitter/Receiver The transmitter/receiver component ofthe cell phone is under the command of the logic/control unit.Powerful 3-watt telephones are typically of the vehicle-mounted or transportable type, and their transmitters areunderstandably larger and heavier than those containedwithin lighter-weight handheld cellular units. These morepowerful transmitters require significantly more inputwattage than hand-held units that transmit at power levelsof only a fraction of a watt, and they use the main batterywithin a vehicle or a relatively heavy rechargeable battery todo so. Special circuitry within the phone enables the trans-mitter and receiver to use a single antenna for full-duplexcommunication.Antenna The antenna for a cellular telephone can consist ofa flexible rubber antenna mounted on a hand-held phone, anextendible antenna on a pocket phone, or the familiar curlystub seen attached to the rear window of many automobiles.Antennas and the cables used to connect them to radiotransmitters must have electrical performance characteris-tics that are matched to the transmitting circuitry, fre-quency, and power levels. Use of antennas and cables thatare not optimized for use by these phones can result in poorperformance. Improper cable, damaged cable, or faulty con-nections can render the cell phone inoperative.Power Sources Cell phones are powered by a rechargeablebattery. Nickel-cadmium (NiCd) batteries are the oldest and
  56. 56. 40 CELLULAR TELEPHONEScheapest power source available for cellular phones. Newernickel–metal hydride (NiMH) batteries provide extend talktime compared to lower-cost conventional NiCd units. Theyprovide the same voltage as NiCd batteries but offer at least30 percent more talk time than NiCd batteries and takeapproximately 20 percent longer to charge. Lithium ion batteries offer increased power capacity andare lighter in weight than similar-size NiCd and NiMH bat-teries. These batteries are optimized for the particularmodel of cellular phone, which helps ensure maximumcharging capability and long life. Newer cellular phones may operate with optional high-energy AA alkaline batteries that can provide up to 3 hoursof talk time or 30 hours of standby time. These batteries takeadvantage of lithium–iron disulfide technology, whichresults in 34 percent lighter weight than standard AA 1.5-volt batteries (15 versus 23 grams per battery) and 10-yearstorage life—double that of standard AA alkaline batteries. Vehicle-mounted cell phones can be optionally poweredvia the vehicle’s 12-volt dc battery by using a battery elimi-nator that plugs into the dashboard’s cigarette lighter. Thissaves useful battery life by drawing power from the vehicle’sbattery and comes in handy when the phone’s battery hasrun down. A battery eliminator will not recharge the phone’sbattery, however. Recharging the battery can only be donewith a special charger. Lead-acid batteries are used to power transportable cellu-lar phones when the user wishes to operate the phone awayfrom a vehicle. The phone and battery are usually carried ina vinyl pouch.Features and OptionsCellular telephones offer many features and options, includingG Voice activation Sometimes called “hands-free operation,” this feature allows the user to establish and answer calls by
  57. 57. CELLULAR TELEPHONES 41 issuing verbal commands. This safety feature enables a dri- ver to control the unit without becoming visually distracted.G Memory functions These allow storage of frequently called numbers to simplify dialing. Units may offer as few as 10 memory locations or in excess of 100, depending on model and manufacturer.G Multimode This allows the phone to be used with multiple carriers. The phone can be used to access digital service where it is available and then switch to an analog service of another wireless carrier when roaming.G Multiband This allows the phone to be used with multi- ple networks using different frequency bands. For exam- ple, the cell phone can be used to access the 1900-MHz band when it is available and then switch to the 800- MHz band when roaming.G Visual status display This conveys information on num- bers dialed, state of battery charge, call duration, roaming indication, and signal strength. Cell phones differ widely in the number of characters and lines of alphanumeric information they can display. The use of icons enhances ease of use by visually identifying the phone’s features.G Programmable ring tones Some cellular phones allow the user to select the phone’s ring tone. Multiple ring tones can be selected, each assigned to a different caller. A vari- ety of ring tones may be downloaded from the Web.G Silent call alert Features include visual or vibrating noti- fication in lieu of an audible ring tone. This can be partic- ularly useful in locations where the sound of a ringing phone would constitute an annoyance.G Security features These include password access via the keypad to prevent unauthorized use of the cell phone as well as features to help prevent access to the phone’s tele- phone number in the event of theft.G Voice messaging This allows the phone to act as an answering machine. A limited amount of recording time
  58. 58. 42 CELLULAR TELEPHONES (about 4 minutes) is available on some cell phones. However, carriers also offer voice-messaging services that are not dependent on the phone’s memory capacity. While the phone is in standby mode, callers can leave messages on the integral answering device. While the phone is off, callers can leave messages on the carrier’s voice-mail sys- tem. Users are not billed for airtime charges when retriev- ing their messages.G Call restriction This enables the user to allow use of the phone by others to call selected numbers, local numbers, or emergency numbers without permitting them to dial the world at large and rack up airtime charges.G Call timers These provide the user with information as to the length of the current call and a running total of air- time for all calls. These features make it easier for users to keep track of call charges.G User-defined ring tones These offer users the option to compose or download ring tones of their choice to replace the standard ring tone that comes with the cell phone.G Data transfer kit For cell phones that are equipped with a serial interface, there is software for the desktop PC that allows users to enter directory information via keyboard rather than the cell phone keypad. The information is transferred via the kit’s serial cable. Through the software and cable connection, information can be synchronized between the PC and cell phone, ensuring that both devices have the most recent copy of the same information.Location-Reporting TechnologyMobile phone companies are under orders from the FCC toincorporate location-reporting technology into cellularphones. Dubbed E-911, or enhanced 911, the initiative ismeant to provide law enforcement and emergency servicespersonnel with a way to find people calling 911 from mobilephones when callers do not know where they are or are
  59. 59. CELLULAR TELEPHONES 43unable to say. Since no carrier was able to make an October2001 deadline to fully implement E-911, the FCC issuedwaivers permitting carriers to add location-detection ser-vices to new phones over time so that 95 percent of all mobilephones will be compliant with E-911 rules by 2005. One way manufacturers can address this requirement is byproviding cell phones with a Global Positioning System (GPS)capability in which cell phone towers help GPS satellites fix acell phone caller’s position. Special software installed in thebase station hardware serves location information to cellphones, which is picked up at the public safety answeringpoint (PSAP). However, subscribers would need to purchase anew GPS-equipped handset, since this method would not allowlegacy handsets to use the location-determination system. Another location-determination technique is called “TimeDifference of Arrival” (TDOA), which works by measuringthe exact time of arrival of a handset radio signal at three ormore separate cell sites. Because radio waves travel at afixed known rate (the speed of light), by calculating the dif-ference in arrival time at pairs of cell sites, it is possible tocalculate hyperbolas on which the transmitting device islocated. The TDOA technique makes use of existing receiveantennas at the cell sites. This location technique workswith any handset, including legacy units, and only requiresmodifications to the network.Internet-Enabled Mobile PhonesInternet-enabled mobile phones potentially represent animportant communications milestone, providing users withaccess to Web content and applications, including the abilityto participate in electronic commerce transactions. TheWireless Application Protocol (WAP), an internationallyaccepted specification, allows wireless devices to retrievecontent from the Internet, such as general news, weather,airline schedules, traffic reports, restaurant guides, sportsscores, and stock prices.
  60. 60. 44 CELLULAR TELEPHONES Users also can personalize these services by creating aprofile that might request updated stock quotes every half-hour or specify tastes in music and food. A user also could setup predefined locations, such as home, main office, or tran-sit, so that the information is relevant for that time and loca-tion. With access to real-time traffic information, forexample, users can obtain route guidance on their cell phonescreens via the Internet. Up-to-the-minute road conditionsare displayed directly on the cell phone screen. Street-by-street guidance is provided for navigating by car, subway, orsimply walking, taking into account traffic congestion towork out the best itinerary. Such services can even locateand guide users to the nearest facilities, such as free parkinglots or open gas stations, using either an address entered onthe phone keypad or information supplied by an automaticlocation identification (ALI) service. One vendor that has been particularly active in develop-ing WAP-compliant Internet-enabled mobile phones isNokia, the world’s biggest maker of mobile phones. Thecompany’s Model 7110 works only on GSM 900 and GSM1800 in Europe and Asia but is indicative of the types of newmobile phones that about 70 other manufacturers are tar-geting at the world’s 200 million cellular subscribers. It dis-plays Internet-based information on the same screen usedfor voice functions. It also supports Short MessagingService (SMS) and e-mail and includes a calendar andphonebook as well. The phone’s memory also can save up to 500 messages—SMS or e-mail—sorted in various folders such as the inbox,outbox, or user-defined folders. The phonebook has enoughmemory for up to 1000 names, with up to five phone and faxnumbers and two addresses for each entry. The user canmark each number and name with a different icon to signifyhome or office phone, fax number, or e-mail address, forexample. The phone’s built-in calendar can be viewed by day,week, or month, showing details of the user’s schedule andcalendar notes for the day. The week view shows icons for the
  61. 61. CELLULAR TELEPHONES 45jobs the user has to do each day. Up to 660 notes in the cal-endar can be stored in the phone’s memory. Nokia has developed several innovative features to makeit faster and easier to access Internet information using amobile phone:G Large display The screen has 65 rows of 96 pixels (Figure C-3), allowing it to show large and small fonts, bold or reg- ular, as well as full graphics.G Microbrowser Like a browser on the Internet, the micro- browser feature enables the user to find information by entering a few words to launch a search. When a site of interest is found, its address can be saved in a “favorites” folder or input using the keypad.G Navi Roller This built-in mouse looks like a roller (Figure C-4) that is manipulated up and down with a finger to scroll and select items from an application menu. In each situation, the Navi Roller knows what to do when it is clicked—select, save, or send.G Predictive text input As the user presses various keys to spell words, a built-in dictionary continually compares the word in progress with the words in the database. It selects the most likely word to minimize the need to con- tinue spelling out the word. If there are several word pos- sibilities, the user selects the right one using the NaviFigure C-3 Display screen of the Nokia 7110.
  62. 62. 46 CELLULAR TELEPHONESFigure C-4 Close-up of the Navi Roller on the Nokia 7110. Roller. New names and words can be input into the phone’s dictionary. However, the Nokia phone cannot be used to access justany Web site. It can access only Web sites that have beendeveloped using WAP-compliant tools. The WAP standardincludes its own Wireless Markup Language (WML), whichis a simple version of the HyperText Markup Language(HTML) that is used widely for developing Web content. Thestrength of WAP is that it is supported by multiple airlinkstandards and, in true Internet tradition, allows contentpublishers and application developers to be unconcernedabout the specific delivery mechanism.Third-Generation PhonesThe world is moving toward third-generation (3G) mobilecommunications systems that are capable of bringing high-quality mobile multimedia services to a mass market.The International Telecommunication Union (ITU) hasput together a 3G framework known as InternationalMobile Telecommunications-2000 (IMT-2000). This frame-work encompasses a small number of frequency bands,available on a globally harmonized basis, that make use ofexisting national and regional mobile and mobile-satellitefrequency allocations.