30 September 1997
Source: Bill Stewart <stewarts@ix.netcom.com>

 (Converted by others from original Microsoft Word to HTML using MSOffice97; page numbers and other formatting have changed.) Zipped original in Microsoft Word (598K).

AT&T Digital PCS White Paper

AT&T Wireless Services

Corporate Communications

Kirkland, Washington 98033


Todd Wolfenbarger

Ken Woo






  1. Executive Summary 3
  2. Overview of AT&T Digital PCS 4
  3. Security Issues 7
  4. Coverage 10
  5. Industry Support 11
  6. Comparison to other digital technologies 12
  7. Technical Description 13
  8. Glossary 16



Executive Summary


AT&T’s Digital PCS product is based on the North American IS-154 TDMA digital standard approved by the Telecommunications Industry Association (TIA) in 1989. AT&T Wireless Services makes no distinction between so called "cellular frequencies" in the 800 Mhz. range and newer frequencies sometimes referred to as "PCS" frequencies at the 1900 Mhz. range. AT&T’s research indicates consumers do not care whether their calls are handled in the 800 or 1900 range. Consumer research indicates customers only care about their wireless phones working anytime, anywhere. Therefore, AT&T has elected to brand its digital product, "Digital PCS," which stands for digital personal communication services---a digital platform for AT&T customers that supplies features such as:



In addition, AT&T’s Digital PCS phone also provides an analog default in the event a caller travels into a non-digital signal coverage area. Defaulting to analog allows voice and data conversations to continue. Digital platform features are unavailable until the caller travels back into a digital signal coverage area.


AT&T’s Digital PCS system is the most widely available system in North America today.



Overview of AT&T’s Digital PCS


AT&T Wireless Services first deployed digital TDMA into its national network in 1993. The first releases of TDMA for wireless users allowed for lower operating costs and enhanced voice privacy.


TDMA’s introduction into the AT&T Wireless network actually debuted during Hurricane Andrew in Florida. The technology had been set up in the Florida system first and was undergoing testing when the hurricane struck. The unused digital network was tapped into service to initially support police, fire, search and rescue personnel, the American Red Cross and the Federal Emergency Management Agency. The digital network was used to assess damage, summon aid and disperse emergency supplies to people in need.


Later in the storm’s aftermath, the digital system was used to support emergency calls by local residents who did not have regular landline service to contact friends and relatives in other parts of the country to let them know they were o.k.


Over the course of 1993-1996, the company spent considerable time and energy helping the technology evolve. On October, 1996, the company introduced the latest revision of TDMA known as IS-136 and named its service AT&T Digital PCS.


IS-136 is the latest generation of wireless communications and is the cutting edge technology around which AT&T Digital PCS is built. It is a set of protocols than enable phones and cell sites to communicate with one another.


AT&T Digital PCS is currently being deployed around the U.S. and Canada. Seventy million potential customers in more than 40 metropolitan areas throughout the U.S. now have access to unparalleled convenience, value and increased peace of mind. These initial major markets include:



In addition, other major carriers such as BellSouth, SBC Communications and portions of Bell Atlantic Mobile Systems have also deployed TDMA technology for mobility networks. By 1998, AT&T Wireless will have deployed dual-mode, dual band phones that will allow customers to use services in both 800 and 1900 markets. AT&T’s digital mobile wireless footprint is licensed to cover approximately 80% of the U.S. population.


Major industry analysts say the trend toward digital is clear. Digital technology offers platforms for many new services consumers want. Demand will continue to grow.


Digital Subscriber Forecast 1997-2005

Millions of Customers

The Yankee Group, a prominent research and industry analyst organization predicts an average 59% compounded annual growth rate (CAGR) for digital wireless technology. By the year 2005, The Yankee Group predicts

nearly 50% of all wireless users will be on digital platforms.


SOURCE: The Yankee Group: An Update on Digital Cellular & PCS, January 30, 1997





Carriers are migrating toward digital technology because it provides increased capacity and flexibility for new services. There are three major technologies in North America. TDMA is supported by AT&T Wireless Services. CDMA is being used by companies like PrimeCo and Sprint PCS. GSM is used by companies like Western Wireless and Pacific Bell Mobile Systems. All technologies are digital and all technologies do basically the same thing as illustrated on the table on page 11. The main differences are that TDMA is more widely deployed and has more flexibility for in-building and on-campus wireless PBX applications. It is against this backdrop that TDMA is predicted to dominate wireless digital standards into the next century.




Herschel Shosteck & Associates says that TDMA’s maturity, dropping handset prices and the AT&T marketing prowess will continue to power the growth of TDMA as a dominant standard in North America. Shosteck says CDMA has yet to reach maturity and also faces challenges of network tuning and higher handset prices, thus impeding system roll outs. He predicts by the year 2000, CDMA terminals will comprise 31% of total sales.


Digital Marketing Forecast - TDMA v. CDMA

Percent of Phone Sales

Shosteck says digital is not about technology. It is about marketing prowess and brand names associated with carriers advocating the technology. It’s also about the packaging of the services and handsets which those carriers provide.


SOURCE: Herschel Shosteck & Associates, Digital Marketing Forecasts, January 1997.



While the numbers may be slightly different, the Strategis Group, formerly MTA-EMCI Telecommunications Consultants, another highly respected industry research group, agrees with Shosteck’s analysis. Strategis predicts digital wireless will clearly surpass analog wireless communications beginning in 1998. Their forecast is that 80% of users will have digital technology by the year 2002.



Security Issues


All digital phones have control channels that transmit and receive authentication codes, which help prevent phone cloning and eavesdropping. AT&T Digital PCS handsets utilizes "shared secret data authentication," also known as SSD. It uses a common authentication key in the phone and in the network. At the time a phone is switched "on," a 64 bit "A" key is entered into the unit and into the network in a database called the Home Location Register (HLR). From the A key, SSD-A and SSD-B are derived and used to authenticate the telephone set and establish a voice privacy key.


Summary of Support for Security Requirements

AT&T Digital PCS vs. Analog/AMPS Handsets (Most)


AT&T Digital Quality


Privacy of Communications










Billing Accuracy



Privacy of User Information




User ID



Calling Patterns



Theft Resistance of Phone

Over the air



From network



From interconnection






Handset Design

Algorithms run in

Algorithms run in

microprocessor of

microprocessor of



Law Enforcement Needs

Must wiretap at the

Eavesdropping can

MSC or with

be done with a

sophisticated equip.



All wireless phones are assigned an electronic serial number (ESN) at the time of manufacturing. TDMA IS-136 phones are also assigned a 15 digit International Mobile Subscriber Identity (IMSI) that is unique world-wide, an A-key and other data at the time of service installation. When the phone is switched on, it must electronically register with the system by sending its IMSI and other data to the wireless network.


On the control channel, the radio system transmits a random number, RAND, that is received by all digital phones on the network. When a digital phone accesses the network, it calculates a cryptographic response using and algorithm known as "CAVE."


The encrypted version of RAND, using a derivative of the A-key called SSD-A, is then transmitted to the network, where it is verified. The network does the same calculation and confirms the identity of the digital phone. All transmissions between the phone and network are encrypted to prevent decoding of the data and using the data to clone other phones. Furthermore, each time a digital phone places or receives a call, a call counter is incremented. The counter is also used for clone detection since clones can not have a call history identical to the legitimate phone.


Procedures have been designed to permit a system to challenge an individual phone with a unique challenge and to update the SSD.


Breaking the Algorithm?


In March, 1997, several computer technicians claimed to have cracked a key part of the electronic code meant to protect the privacy of calls made on the new digital generation of cellular phones. The hackers claim the new phones cannot live up to manufacturers' claims of being more secure than traditional analog cellular phones.


The algorithm they claim to have broken is an unused element within the AT&T digital network. Overall voice and data transmissions are still secure. Impact on AT&T Wireless digital customers is zero. The Cellular Telecommunications Industry Association (CTIA) issued the following list of questions and answers in response to the claims made by the code-breakers:


Q. Does this mean that eavesdroppers can listen in on my phone calls?

  1. No. The encryption discussed by the researchers involves the algorithm used to encrypt numbers

Q. Is it easy to break this keypad number code?

  1. Not at this time. It involves very sophisticated cryptological knowledge. The digital encryption

Q. What is the impact of this announcement on people who now use wireless digital phones?

  1. Virtually none. To break the coded algorithms protecting the keypad takes sophisticated

Q. Why didn't the wireless phone industry develop phones that have unbreakable security?

  1. Standards for phone technology are developed within the confines of federal regulations and the

Q. Does this announcement have any impact on the industry's efforts to stop phone cloning?

  1. No. During the past year, the industry has been very successful in introducing new technologies that

Q. What is the industry doing about this problem?

  1. The CTIA testified before Congress on February 5, about the need to strengthen the laws protecting

In summary, AT&T’s digital TDMA network provides strong security as follows:







AT&T Digital PCS is the most widely available digital wireless technology across the U.S. and Canada today. AT&T’s wireless digital network is available to 40% of the U.S. as of May, 1997. National coverage is licensed for 80% of the population. In addition, via a marketing and technology agreement with Rogers Cantel, AT&T Digital PCS services are seamlessly available across Canada.


AT&T’s National U.S. Coverage Area



Shaded areas indicate 1900 markets that will come on line over the course of 1997. The dotted cities show existing 800 Mhz. digital service.


AT&T Digital PCS customers will also have an analog default if their phone is used in a non-digital coverage area. In total, AT&T Digital PCS users have wireless access to more than 5,500 locations across North America via the North American Cellular Network (NACN). In addition, with AT&T’s Cell Card service, users also have the ability to have seamless call delivery and use in more than 35 locations across Europe, Asia and Australia.






Industry Support


The TDMA standard is supported by an industry organization called "The Universal Wireless Communication Consortium." The UWC program was launched in 1995 as a collaborative effort among leading vendors and operators of wireless products and services to deliver an enhanced portfolio of global mobility services across all spectral, market and subscriber bands.


The platform for developing and delivering such enhanced personal communications features to subscribers worldwide consists of the TIA IS-136 standard version of TDMA, in combination with the enhanced internetworking and mobility of the IS-41 Wireless Intelligent Network (WIN) standard capabilities. This provides a complete "engineering toolkit" for providing a diversity of public and private wireless service solutions to customers.


The TDMA/WIN platform is the fastest growing solution set for full digital mobility services available today. Member companies include:


AT&T Wireless Services Nokia, Inc.

BellSouth Cellular Corp. Nortel (Northern Telecom)

Rogers Cantel (Canada) Pacific Link Communication Services (HK)

Cellcom (Israel) Southwestern Bell Wireless

Celumovil (Columbia) SPT (Czech Republic)

Ericsson Tandem Computers, Inc.

Hughes Network Systems Telecom New Zealand

Lucent Technologies Vimpelcom (Russia)

Mobilkom (Malaysia)

Movilnet (Venezuela)


The objectives of the consortium are to:



The UWC home page can be found on the Internet at http://www.uwcc.org.


Comparison to Other Wireless Technologies












AWS,SBC, BellSouth

PrimeCo., Sprint PCS

Western Wireless

All major carriers


AirToich, BAMS

APC, BellSouth

operate an AMPS

NYNEX Mobile

Pacific Bell Mobile

analog system

In-Building Services





Roaming Coverage

Seamless across the



Most cities across

US and Canada

US and Canada

Differentiated Billing






Enhanced 8 Kbps

8/13 kbps

13 kbps


Wireless Office Service





Seamless Handoff/Analog





Seamless Handoff/Digital





Price of Phones


Advertised Rate



Average Monthly Bill


Market Specific

Market Specific


Voice Mail





Message Waiting Indicator





Short Messaging










Caller ID*





Extended Battery Life










International Coverage





*Where available through landline carrier

**Only through AT&T Cell Card



Technical Description


TDMA stands for Time Division Multiple Access. TDMA divides the radio spectrum into time slots, and in each slot, only one user is allowed to either transmit or receive.

Each user occupies a cyclically repeating time slot, so that a channel may be thought of as particular time slot that reoccurs every frame. TDMA systems transmit data in a buffer and burst method, thus the transmission for any user is noncontinuous. This implies that, unlike in analog systems, digital data and digital modulation must be used. The transmission from various users is interlaced into a repeating frame structure.


TDMA scheme where each channel occupies a cyclically repeating time slot

N time slots comprise a frame.



A frame consists of a number of slots. Each frame is made up of a preamble, information message and trail bits.


In a TDMA frame, the preamble contains the address and synchronization information that both the base station and the subscribers use to identify each other. Guard times are used to allow synchronization of the receivers between the different slots and frames.




System Features:





A vocoder is a voice coder used in digital phones that consist of a speech analyzer and speech synthesizer. The analyzer circuitry converts analog speech waveforms into digital signals. The synthesizer converts the digital signals into artificial speech sounds. A vocoder is used in wireless handsets to reduce the bandwidth requirements for transmitting digitized speech signals, thereby improving spectral efficiency.


In deploying vocoders, a balance must be struck between the perceived quality of the speech resulting from this compression and the overall system operation and capacity.


Mobile radio channels operate in a hostile transmission medium beset with problems such as fading, multipath, and interference. It is therefore important that the speech codec be robust to transmission errors.


TDMA IS-136 has increased the capacity of the analog system threefold by using an 8 Kbps VSELP speech codec. An enhanced 8 Kbps vocoder is being deployed in new dual-mode, dual band phones that includes a new algorithm that enhances voice quality. Competing technologies argue that a 13 Kbps vocoder is more efficient. However, having limited bandwidth only means that 13 Kbps takes up more spectrum and does not necessarily improve voice quality.


The improved vocoder is made possible by an ACELP (algebraic code excited linear predictive) alogorithm. This is an enhanced, internationally-established code for dividing waves of sound into binary bits of data. The ACELP coder is being incorporated into wireless base station radios as well as new telephone handsets.


As new ACELP-capable phones become widely availablem they will enable customers to take advantage of the improved digital clarity over both North American frequency bands for wireless communications, 850 MHz. and 1.9 GHz.


Why Do We Need Vocoders?


One of the most difficult conditions for speech coders to perform well in is the case where a digital speech-coded signal is transmitted from the mobile phone to the base station, and then demodulated into an analog signal which is then speech-coded for transmission as a digital signal over landline or wireless link. This situation, called tandem signaling, tends to exaggerate the bit errors originally received at the base station. Tandem signaling is difficult to protect against, but is an important evaluation criterion in the evaluation of speech coders.


In summary, despite marketing claims of "better than landline" quality for some vocoders, the fact remains that given the state of radio physics, it is extremely difficult to match mobile calls regardless of type of vocoders used to digital landline quality. The good news, despite the commercial pitches, is that all carriers are working to improve vocoders and overall system quality beyond the current 8 Kpbs vs. 13 Kbps battle.


Wireless Glossary


"A" Carrier: See non-wireline cellular company.


A/B Switch: A feature found on new cellular telephones permitting the user to select either the "A" (non-wireline) carrier or the "B" (wireline) carrier when roaming away from home.


Advanced Intelligent Networks: Systems that allow a wireless user to make and receive phone calls while roaming in areas outside the user's "home" network. These networks, which rely on computers and sophisticated switching techniques, also provide many Personal Communications Services features such as "one person/one phone."


Air Time: Actual time spent talking on the cellular telephone. Most carriers bill customers based on how many minutes of air time they use each month. The more minutes of time spent talking on the phone, the higher the bill.


Alphanumeric: A message or other type of readout containing both letters ("alphas") and numbers ("numerics"). In cellular, "alphanumeric memory dial" is a special type of dial-from-memory option that displays both the name of the individual and that individual's phone number on the cellular phone handset. The name also can be recalled by using the letters on the phone keypad. By contrast, standard memory dial recalls numbers from number-only locations.


AMPS: Advanced Mobile Phone Service is the term used by AT&T's Bell Laboratories (prior to the break-up of the Bell System in 1984) to refer to its cellular technology. The AMPS standard has been the foundation for the industry in the United States, although it has been slightly modified in recent years . "AMPS-compatible" means equipment designed to work with most cellular telephones.


Analog: The traditional method of modulating radio signals so that they can carry information. AM (amplitude modulation) and FM (frequency modulation) are the two most common methods of analog modulation. Though most U.S. cellular systems today carry phone conversations using analog, some have begun offering digital transmission. See also Digital modulation.


Antenna: A device for transmitting and/or receiving signals. The size and shape of antennas are determined, in large part, by the frequency of the signal they are receiving.


"B" Carrier: See wireline cellular company.


Bandwidth: A relative range of frequencies that can carry a signal without distortion on a transmission medium.


Base Station: The central radio transmitter/receiver that maintains communications with mobile radiotelephone sets within a given range (typically a cell site).


BTA: Basic Trading Area. A service area designed by Rand McNally and adopted by the FCC to promote the rapid deployment and ubiquitous coverage wireless service at 1900 MHz. and a variety of services and providers. There are 493 BTAs in the United States.


CDMA: Code Division Multiple Access. A spread-spectrum approach to digital transmission. With CDMA, each conversation is digitized and then tagged with a code. The mobile phone is then instructed to decipher only a particular code to pluck the right conversation off the air. The process can be compared in some ways to an English-speaking person picking out in a crowded room of French speakers the only other person who is speaking English. CDMA technology offers three features that improve system quality: (1) The "soft hands-off" feature ensures the call is connected before hand-off is completed, reducing the probability of a dropped call. (2) Variable rate vocoding allows speech bits to be transmitted at only the rates necessary for high quality, which conserves the battery power of the handset. (3) Multipath signal processing techniques combines power for increased signal integrity. Spread spectrum takes the original information and combines it with a correlating code, resulting in a signal which occupies a much greater bandwidth than the original. By assigning a unique correlating code to each transmitter, several simultaneous conversations can share the same frequency allocation.


CDPD: Cellular Digital Packet Data. Technology that allows data files to be broken into a number of "packets" and sent along idle channels of existing cellular voice networks. By adding CDPD to a network, cellular operators can transmit data eight times faster without having to go to the trouble of building a whole new digital platform.


Cell: The basic geographic unit of a cellular system. Also, the basis for the generic industry term "cellular." A city or county is divided into smaller "cells," each of which is equipped with a low-powered radio transmitter/receiver. The cells can vary in size depending upon terrain, capacity demands, etc. By controlling the transmission power, the radio frequencies assigned to one cell can be limited to the boundaries of that cell. When a cellular phone moves from one cell toward another, a computer at the Mobile Telephone Switching Office (MTSO) monitors the movement and at the proper time, transfers or hands off the phone call to the new cell and another radio frequency. The hand-off is performed so quickly that it's not noticeable to the callers.


Cell Splitting: A means of increasing the capacity of a cellular system by subdividing or splitting cells into two or more smaller cells.


CGSA: Cellular Geographic Service Area. The actual area in which a cellular company provides cellular service. This area may be somewhat smaller than the MSA surrounding it.


Channel: A path along which a communications signal is transmitted.


Commercial Mobile Radio Service: The regulatory classification that the FCC uses to govern all commercial wireless service providers including Personal Communications Services, cellular and Enhanced Specialized Mobile Radio.


Counterfeit "Clone" Phone: A sophisticated type of fraud in which a criminal does not pretend to be an out-of-town roamer but rather a legitimate local customer. With this type of fraud, the criminal puts into a phone a computer chip that can be programmed with both the ESN and MIN of a legitimate user. The criminal obtains valid number combinations either through illegally used test equipment or through an unscrupulous employee of a retail agent or carrier.


Counterfeit "Lifetime" Phone: This type of fraud enables thieves to re-program a special wireless phone through its own keypad so that wireless bills are charged to someone else. With the "lifetime" counterfeit phone technology, numerous legitimate MIN/ESN pairs can be stored in each phone and the electronic component in a wireless phone that matches the ESN with the MIN can be reprogrammed in less than one minute.


Counterfeit "Tumbler" Phone: In late 1990, a new sophisticated type of crime emerged known as "tumbling ESN" fraud. This type of fraud would alter a wireless phone so it would tumble through a series of ESNs and make the caller appear to be another new customer each time a call was made. By replacing the Number Assignment Module (NAM), an electronic component in a wireless phone that matches the ESN with the MIN, a typical tumbler caller had the ability to generate 48,000 possible ESNs.


Digital Modulation: A method of encoding information for transmission. Information, or in this case, a voice conversation, is turned into a series of digital bits -- the 0s and 1s of computer binary language. At the receiving end, the information is reconverted. Digital transmission offers a cleaner signal and is virtually immune to the problems that plague analog modulation such as fading and static. (To appreciate the difference, compare the fidelity of a standard LP record, complete with background noise caused by dust hiss, with that of a digital compact disk.) Digital transmission also has been embraced by the wireless industry because it offers major gains in capacity compared to analog. See also CDMA and TDMA.


Erlang: A measurement of telephone traffic. One Erlang is equal to one full hour of use (e.g. conversation)m or 60x60=3,600 seconds of phone conversation. You convert CCS (hundred call seconds) into Erlangs by multiplying by 100 and then dividing by 3,600 (i.e. dividing by 36). Numerically, traffic on a trunk group, when measured in erlangs, is equal to the average number of trunks in use during the hour in question. Thus, if a group of trunks carries 12.35 erlangs during an hour, a little more than 12 trunks were busy, on average. Erlang gets its name from the father of queuing theory, A.K. Erlang, a Danish telephone engineer, who, in 1908, began to study congestion in the telephone service of the Copenhagen Telephone Company. A few years later, he arrived at a mathematical approach to assist in designing the size of telephone switches. Central to queuing theory are basic facts of queuing life. First, traffic varies widely. Second, anyone who designs a telephone switch to completely handle all peak traffic will find the switch idle for most of the time. He will also find he’s built a very expensive switch. Third, it is possible, with varying degrees of certainty to predict upcoming "busy periods."


ESMR: Enhanced Specialized Mobile Radio. Digital mobile telephone services offered to the public over channels previously used only for analog two-way dispatch.


ESN: Electronic Serial Number. The unique number assigned to a wireless phone by the manufacturer. According to the Federal Communications Commission, the ESN is to be fixed and unchangeable -- a sort of unique fingerprint for each phone.


FCC: Federal Communications Commission. The government agency responsible for regulating telecommunications in the United States.


FDMA: Frequency Division Multiple Access. Method of radio transmission that allows multiple users to access a group of radio frequency bands without interference. Users occupy 25 MHz. of frequency spectrum. The cellular radio band, allocated from 824 MHz. to 849 MHz. and 869 MHz. consists of 416 total channels, or frequency slots, available for conversations. Within each cell, approximately 48 channels are available for mobile users. Different channels are allocated for neighboring cell sites, allowing for reuse of frequencies with a minimum of interference. This technique of assigning individual frequency slots and re-using these frequencies throughout the system, is known as FDMA.


Frequency: A measure of the energy, as one or more waves per second, in an electrical or lightwave information signal. A signal's frequency is stated in either cycles-per-second or Hertz (Hz).


Frequency Re-use: The ability to use the same frequencies repeatedly within a single system, made possible by the basic design approach for cellular. Since each cell is designed to use radio frequencies only within its boundaries, the same frequencies can be reused in other cells not far away with little potential for interference. The reuse of frequencies is what allows a cellular system to handle a huge number of calls with a limited number of channels.


Ghz: gigaHertz. Billions of Hertz.


GSM: Groupe Speciale Mobile (now translated in English as Global Standard for Mobile). The Pan-European digital cellular system standard.


Hand-off: The process by which the Mobile Telephone Switching Office passes a cellular phone conversation from one radio frequency in one cell to another radio frequency in another. It is performed so quickly that callers don't notice.


Hands-Free: A feature that permits a driver to use a wireless car phone without lifting or holding the handset. An important safety feature.


Hertz: A measurement of electromagnetic energy, equivalent to one "wave" or cycle per second.


Khz: kilohertz (thousands of Hertz).


Kilo: The prefix indicating 1,000 times a value. For example, 1 kilovolt (kV) = 1,000 volts.


Message Alert: (also called a "call-in-absence" indicator) A light or other indicator on a wireless phone that notifies a user that a call has come in. a useful feature especially if the cellular subscriber has voice mail.


Mhz: megaHertz. (millions of Hertz).


MIN: Mobile Identification Number. A number assigned by the wireless carrier to a customer's phone. The MIN is meant to be changeable, since the phone could change hands or a customer could move to another city.


Mobile Satellite Service: Communications transmission service provided by satellites. A single satellite can provide coverage to the whole United States.


Mobile, or Car Phone: A type of cellular phone that is permanently installed in a car or truck. It transmits at about 3 watts of power, runs off the vehicle's battery, and uses an external antenna.


MSA: Metropolitan Statistical Area. An MSA denotes one of the 306 largest urban population markets as designated by the U.S. government. Two cellular operators are licensed in each MSA.


MTA: Major Trading Area. A Personal Communications Services area designed by Rand McNally and adopted by the FCC. There are 51 MTAs in the United States.


MTSO: Mobile Telephone Switching Office. The central computer that connects a cellular phone call to the public telephone network. The MTSO controls the entire system's operations, including monitoring calls, billing and handoffs.


NAM: Number Assignment Module. The NAM is the electronic memory in the cellular phone that stores the telephone number and electronic serial number.


No-answer Transfer: A service provided by cellular carriers that automatically transfers an incoming cellular call to another phone number if the cellular subscriber is unable to answer. Most no-answer transfer systems will automatically transfer the call on the first ring if the cellular phone is turned off, but will not make the transfer until the third or fourth ring if the phone is turned on.


Non-wireline Cellular Company: The Block "A" carrier. The "A" originally stood for "alternate," i.e. the non-Bell or "B" carrier in a market. The FCC, in setting up the licensing and regulatory rules for cellular, decided to license two cellular systems in each market. It reserved one for the local telephone company, and opened a second system -- the Block A system -- to other interested applicants. The distinction between Block A and Block B is meaningful only during the licensing phase at the FCC. Once a system is constructed, it can be sold to anyone. Thus in some markets today, both the A and B systems are owned by telephone companies -- one happens to be the local phone company for the area and the other is a phone company that decided to buy a cellular system outside its home territory.


Off-peak: The periods of time after the business day has ended during which carriers offer discounted air time charges.


Peak: That part of the business day in which cellular customers can expect to pay full service rates.


PCS - Personal Communication Services: Some definitions would indicate this is new technology and improved technology over cellular. Quite often, this definition refers to new license holders in the 1.9 gHz. range. AT&T Wireless Services does not see PCS as new technology, but rather as a service concept - Personalized Communication Services. The analogy of your car radio is useful here, since the argument is between what is defined as traditional cellular in the 800 MHz. range and new license holders in the 1900 range. If you listen to a favorite station at 710 on your AM dial, for example, when you switch to another favorite station at 1070 on the AM dial---that is not new technology. You are just tuning to another station on a higher band. It is the same between 800 and 1900. You are just moving to a higher end of the band.


POP: Short for population. One "POP" equals one person. In the wireless industry, systems are valued financially based on the population of the market served.


Portable: A small, lightweight handset that fits in a suit pocket or purse and transmits at no more than .6 watts of power provided by a small rechargeable battery.


Propagation Delay: The delay caused by finite speed at which electronic signals can travel through a transmission medium. Propagation delay is estimated at 160 million meters per second in copper wire. NOTE: no SIGNAL can travel through any medium faster than the speed of light, which is 300 million meters per second, or 186,000 miles per second.


Propagation Time: Time required for an electrical wave to travel between two points.


Propagation Velocity: The speed at which electrons or photons travel.


Roaming: The ability to use a cellular phone to make and receive calls in places outside your home calling area.


RSA: Rural Service Area. One of the 428 FCC-designated rural markets across the United States.


Satellite/Cellular Phone: A dual mode wireless phone that uses Mobile Satellite Service when it is out of range of the cellular network coverage.


Service Charge: The amount you pay each month to receive cellular service. This amount is fixed, and to be paid monthly regardless of how much or how little you use your cellular phone.


SMR: Specialized Mobile Radio. Private business service using mobile radiotelephone and base stations communicating via the public phone network.


Spread Spectrum: Also called frequency hopping, spread spectrum is a modulation technique in which the information content is spread over a wider bandwidth than the frequency content of the original information. Spread spectrum takes an input signal, mixes it with FM noise and "spreads" the signal over a broad frequency range, hopping from frequency to frequency at split second intervals. The spread signal has greater bandwidth than the original message. Spread spectrum receivers recognize a spread signal, acquire it, and "de-spread" it and thus returns it to its initial form (the original message). Spread spectrum is highly secure. Would be eavesdroppers hear only unintelligible blips. Attempts to jam the signal succeed only at knocking out a few small bits of it. So effective is the concept that it is now the principal anti-jamming device in the U.S. government’s Milstar Defense Satellite Communications System.


Standby Time: The amount of time you can leave your fully charged, wireless portable or transportable turned on before the phone's battery will run down.


Talk Time: The length of time you can talk on your portable or transportable wireless phone without recharging the battery. The battery capacity of a phone is usually expressed in terms of "minutes of talk time" or "hours of standby time." When you're talking, the phone draws more power from the battery.


TDMA: Time Division Multiple Access. A method of digital wireless communications transmission allowing a large number of users to access (in sequence) a single radio frequency channel without interference by allocating unique time slots to each user within each channel.


Transportable: A standard 3-watt mobile phone that can be removed from a car and used by itself with an attached battery pack. The entire unit is generally mounted or built into a custom carrying case to make it easy to carry. Although technically "portable," the transportable should not be confused with the handheld, one-piece wireless phone.


Voice Mail: (also called voice messaging) A computerized answering service that answers a call, plays a greeting and records a message. Depending on the sophistication of the service, it also can notify you via a pager that you have received a call. After you have retrieved your messages, you can delete them, save them, reply to them or forward them to someone else on your voice mail system.


Voice-activated Dialing: A feature that permits you to dial a phone number by speaking it to your wireless phone instead of punching it in yourself. The feature contributes to convenience as well as driving safety.


Wireless: Describing radio-based systems allowing transmission of telephone and/or data signals through the air without a physical connection, such as a metal wire or fiber optic cable.


Wireline Cellular Carrier: (Also called the Block "B" carrier) Under the FCC's initial cellular licensing procedures, the Block B carrier is the local telephone company. The FCC reserved one of the two systems in every cellular market for the local telephone, or wireline, company. After initial licensing, the distinction can disappear. The local phone company can sell its cellular system to anyone.