Telecommunications Glossary

Select the first letter of the word from the list below to jump to appropriate section of the glossary. If the term you are looking for starts with a digit or symbol, choose the '#' link. Many terms contain Hyperlinks to appropriate sites.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z #


Acoustic Coupler
This is a special cradle in which you place the handset of a phone. This is connected to a modem, and the modem accesses the phone line through this coupler. Modern modems connect directly to the phone line.

Analogue refers to signals that can represent an infinite range of numbers, as opposed to digital which can only be distinct whole numbers. Analogue data often comes from measurements, like a sine wave. The sound a modem makes over the phone is analog since it can be any of a number of different frequencies. The fixed-line networks usually transfer analogue data and fax. The GSM networks are Digital.

ANSI graphics is a set of cursor control codes which originated on the VT100 smart terminal. Many BBS's use these codes to help improve the sending of characters to communications programs. It uses the escape character, followed by other characters, which allows movement of the cursor on the screen, a change of color, and more.

A program and database which locates files on the Internet.

From ARPA (Advanced Research Projects Agency) and network. An early experimental network.

American Standard Code of Information Interchange. It uses 7 bits to represent all uppercase and lowercase characters, as well as numbers, punctuation marks, and other characters. ASCII often uses 8 bits in the form of bytes and ignores the first bit.

ASCII transfer
When a text file is sent directly as it is, without any special codes.

Asynchronous Transmission
Transmission method in which the intervals between transmitted characters may be unequal of length. Transmission is controlled by start and stop bits at the beginning and end of each character. This way, if there is line noise, the modem can find out right away where the next byte should start. [See Synchronous communication].

AT command
Any instructions sent to a modem that begin with "AT". See also Hayes AT command set.

AT command set
See Hayes AT command set.

Attention characters
The letters "AT", which get the modem's attention that you are about to send it a command. [See also Hayes AT command set].

Auto Reliable
The ability of a modem to be able to communicate both with modems that do have error-control and/or data compression, and those that do not.



The difference between the upper and lower limits of a band. A range of radio, audio, or other frequencies. Since it is so limited, a modem must carefully change data into sounds that "fit" within this range. Similar to frequency spectrum. Bandwidth of a voice channel is 3000Hz-300Hz which equals 2700Hz. Telephone lines have a bandwidth from 300 hertz to 3400 hertz.

Beginners All-purpose Symbolic Instruction Code. It is a programming language. It is called symbolic because it allows programmers to use symbols to represent numbers and information. In algebra, these symbols are called variables.

Balanced/unbalanced. A device which connects a balanced (two-wire) line, such as a phone line, to an unbalanced (coaxial) line, like cable. The two-wire line is called balanced because the currents in each wire are equal and in opposite directions.

A term referring to the speed at which modems communicate. Technically, it is the number of changes in an electronic signal per second. Since the number of changes used to be the same as the number of bits sent or received per second, bps and baud are often used interchangeably. However, there is a difference, which is very often confused. For example, many 1200bps modems were advertised as 1200 baud, even though they operate at 600 baud. They send out 2 bits 600 times a second, which means that it is 600 baud. However, since it is so often misunderstood, you can assume that when you see "baud" it means bits per second, unless it is stated otherwise. The term comes from the scientist J. M. E. Baudot. [See also bps].

Binary File Transfer

Billion Rand
What it costs to start a cellular network

A Binary digIT. It is a number in base 2 (binary), which means that it can only be a 0 or a 1. It is used in the expres-sion `bits per second'. [See also byte].

Bits Per Second. The transmission speed of most modems is measured in baud or bps. Bps is literally the number of bits sent by the modem every second. [See also baud].

Block size
When used with either error control or data compression protocols, refers to the number of characters to be sent at one time. If error control is used, the codes are sent immediately following this block. Typical block sizes are 64, 128, 192, or 256 characters. Small block sizes are better when the line quality is bad (such as for long distance calls), while large block sizes are better during good connections (such as for local calls).

A group of 8 bits. It usually represents one character.



Consultative Committee International on Telephones and Telegraphy. Used to set standards for modems. Replaced by the ITU.

Card Services
DOS and Windows 3.1x users must have Card Services enabled to use their computer's PCMCIA slot(s). Card Services simply allows DOS/Windows 3.1 to see and set up the computer's PCMCIA slot. They will automatically allocate a Communications Port (COM 1 to 5) when the Option modem is plugged in. The Option modem can then be accessed by communications programs via the Windows 95-assigned COM port. Windows 95 users DO NOT need to install Card Service as it is built into Windows 95. Notebook users using DOS/Windows 3.1 usually have the Card Services software bundled with their purchase. Option modems come packaged with a PC Card Installation disk that has an install program for these Card Services. You can however download it here.

Carrier Detect
The information as to whether or not the modem senses a carrier, like a fixed-line dialling tone or a data/fax services enabled on a GSM subscription.

Card Information Services. A PCMCIA setup protocol.

Carrier Detect Threshold
A way of measuring how well a modem can detect valid data over noisy phone lines. It is measured in negative dBm's (decibel-milliwatts). The bigger the number (the more negative) the better. For example,45 dBm is better than40 dBm.  

Caller Line ID Presentation. A code that is sent over the phone lines in some areas when a person makes a phone call. This code includes the phone number of the person making the call. Some modems are able to understand this signal, and let you know who is calling you before you answer the phone.

Caller Line ID Restriction. The ability to block someone who you're calling from seeing your number.  

Cellular Digital Packet Radio

The receiver/transmitter a GSM phone connects to; the equivalent of the base station of a cordless phone. A cell can support a number of simultaneous calls.

A number that represents a larger group of numbers in order to check for errors in data transmission. It is commonly used when downloading a program, as well as in error control protocols. The checksum is the result of a mathematical equation, such as adding all the numbers in a block together (although it is usually more complex than that). 

Chip Set
A group of important IC chips on a modem (or other computer peripheral) that are all made by the same manufacturer. While there are many companies that make modems, there are only a few that make the chips for them. Because the chip manufacturer is making the chips for many companies, they produce more chips, and the price of the chips is lower than if each company produced their own. This decreases the price of the modems on the market.

Code Divison Multiple Access. A digital cellular technique invented by Qualcomm.

Complementary Metal Oxide Semiconductor. A chip which uses small amounts of electricity. It is used typically on battery-powered computers and to save configuration information on other computers when they are turned off.

Communications program

A program that controls a modem, and has features that allow the user to do such things as upload, download, etc. It is similar to a terminal program but more sophisticated. An example is Trumpet WinSock for connecting to the Internet, and Windows HyperTerminal.

When one object can work just like another. Although the term is usually used with computers, it is often used with modems. Many modems are compatible with other popular modems.

To make data take up less space. Archiving programs do this, which means that files will take less time to transfer with modems. Many modems now have the ability to automatically compress the information they send and receive. [See also archive, data compression].

COmpressor/DECompressor, the chip inside every digital GSM cellphone that allows the cellphone to tranmsit voice data at high efficiency and speed across the GSM cellular network. The CODEC will trip redundant voice data like when neither party is talking allowing more effcient use of scarse bandwidth.

Conference of European Post and Telecommunications, the European telecommunications authority.

From hacker and safe cracker. A hacker who breaks into computers
Clear To Send. This is when the modem lets the other computer know that it can send information to the other computer. [See also Flow Control, Return To Send].
The method of flow control that uses the CTS and RTS signals. It is built into the hardware, not software. [See also CTS, RTS, flow control].



Data Access Arrangement. A device used to connect modems to the switched telephone network.

Data over GSM
Send digital data over the digital GSM networks. Click here for a tutorial on data and fax transmission over GSM.

Data Circuit Terminating Equipment. Sets up and maintains a data connection link over a communications medium. For example, a modem.
Data Compression
Some modems have the capability to 'squash' data so that it takes up less space. When another modem (that also has this capability) receives the data, it 'unsquashes' the data to its original form. By using data compression, a modem can send information faster. It's a lot like shorthand--all the information is still there, but it takes less space and is quicker. [See also MNP-5, V.42bis].
Data Transmission rate
The speed at which data travels. For example, data may be sent at 115,200bps. Same as transmission rate, transmission speed, data rate. [See also bps].

Decibel refers to one milliwatt. This is used to measure certain levels, such as transmit level.

Data Services Adapter, an alternative interface to PCMCIA for connecting to a fax or data terminal. The Siemens S1 uses a DSA

A system using discrete numbers to represent data. In computer systems, these are the numbers 0 and 1 (for binary). [See also Analogue].

Data Set Ready. This indicates that the modem is on, and ready to accept input from the computer (either commands or data to be sent over the phone line)

Data Terminal Equipment. This is computer equipment which is not directly responsible for communicating, for example, the computer itself and printers. [See also DCE].

Dual Tone Multi-Frequency. This is used in tone dialing. It is a method where 2 distinct tones are sent for each digit dialed.

Data Terminal Ready. The DTR signal is sent from the computer to the modem, to let the modem know that the computer is ready to communicate.



Electronic Data Interchange. Commonly transferred by Internet or X.400 networks

Electrically Erasable Programmable Read-Only Memory

Electronic Frontier Foundation. An organization promoting civil rights in cyberspace. It is leading the fight against the US government's Clipper Chip.

Error Correction
Error Correction. The ability of a modem to notice errors in transmission, and to resend incorrect data. [See also MNP 1-4, LAPM, V.42].

European Telecommunications Standards Institute.

European Conference on Computers, Freedom, and Privacy.

Electronic mail. Messages that are sent to individual people. You choose who to send the message to and only that person receives the message.

European Strategic Program for Research in Information Technologies.

When there is line noise and one or more characters are changed. This is especially noticeable when downloading or uploading a program. In this case the error must be detected, and the data must be re-sent.



Frequently Asked Questions.

Computer security that attemps to keep crackers out.

To write emotional remarks on electronic mail.

Flow control
A method of controlling when information is sent. One method is Xon/Xoff, where a BBS will send information until your computer sends an Xoff (CTRL-S). It will resume sending information when you send an Xon. [See also Xon/Xoff, CTS/RTS].

Full Duplex
A channel providing simultaneous transmission in both directions.



The method of modulation used by GSM is Gaussian Minimum Shift Keying (GMSK), with a BT value of 0.3 at a gross data rate of 270 kb/s.

The standard controlling fax communication.

GSM originally stood for Groupe Speciale Mobile but has been anglicised to Global System for Mobile Communications, an international digital cellular standard. South Africa was one of the first to implement Phase 2 of GSM.

Click here for a brief history of GSM.


Half Duplex
A channel which signals in both directions, but not simultaneously.

What occurs when a cell phone used in a car moves out of the range of one cell and needs to connect to the next available cell. The preceding cell then hands over the connection to the stronger cell.

Hayes AT command set
This is the set of commands used to operate Hayes modems and Hayes compatible modems. Almost all of the commands start with AT.

Hayes compatible
Any modem which operates in the same way as the modems developed by Hayes.

A unit of frequency, which equals cycles per second.



Interactive Manual
A Windows-based modem control and diagnostic program bundled free with each Option 2-in-1 modem. Here you can alter all Hayes AT commands using icons! Just click on the appropriate icon, and the Interactive Manual will instantly alter the modem's settings. You can also change the modem's settings to conform to the PTT specifications of different countries.

The International Standards Organisation, the body responsible for setting world technical standards. It is based in Geneva, Switzerland.

International Telecommunications Union, based in Geneva, Switzerland.
InterWorking Unit. This is the network "modem" where all the digital to analogue (and visa versa) conversions take place within the digital GSM networks





Famous for the Lotus 1-2-3 spreadsheet of the 1980's, and more recently for it's Notes Groupware system. Bought by IBM in 1995.



The world's largest developer and publisher of software based in Redmond, Seattle, USA. Headed by William (Bill) Gates, the richest (non-royal) person on this planet.

A process whereby a signal is transformed from its original form into a signal that is more suitable for transmission over the medium between transmitter and receiver.

A GUI (Graphical User Interface) for accessing the hypertext WWW (World Wide Web) on the Internet.


Microcom Networking Protocol. Error control and data compression techniques, created by Microcom, that many newer modems use. They are built into the modem, unlike software error correction in file transfer protocols. There are different MNP levels. Levels 1-4 are error control protocols, and level 5 is a data compression protocol that can compress data to about 50% of its original size. A modem with MNP-5 also has MNP-4. MNP 1-4 is also included in the ITU V.42 error correction system.

MNP normal mode
This is the more common mode used with modems that have MNP capability, where the speed from the computer to the modem can be higher than the connection between the modem and the remote modem. This mode uses buffering to prevent lost data.

Memorandum of Understanding, the GSM body that overseas GSM standards and implementation around the world. It comprises operators and some manufacturers.

A MOdulator DEModulator computer peripheral which allows a computer to communicate over telephone lines. This is the heart of computer telecommunications. The main factor that differentiates modems is their speed, measured in bps. Analogue modems talk to one another by converting digital info from the computer into tones called PSK’s. An ordinary analogue modem cannot be physically connected to a GSM phone because networks will not carry PSK tones.



National Center for Automated Information Research.

Network Operators
The folks who install and maintain GSM cellular networks. Click here to see a list of GSM operators around the world. Click here to see the South African network operators.

Non-Transparent Cellular Data
Non Transparent phones use a special error correction technique called RLP. Transparent phones data not incorprate the RLP error corerction techniqure and their data MIGHT be corrupted.




Private Branch Exchange. This is the telephone system that many offices have, allowing extensions for each telephone, and a connection to the main telephone system.
Parity Bit
Most modems have the capability to send an extra bit for every byte sent, which is used to help sense errors. This is called the parity bit. It can be set to no parity, mark parity, space parity, odd parity or even parity. Most BBS's do not use a parity bit. [See also 8-N-1].
PC Cards
Previously known as PCMCIA cards, these are credit card devices used in notebooks and desktop readers for inter alia, data/fax, storage, GPS puposes.

A credit card sized card that generally plugs into a notebook computer. It conforms to the Personal Computer Memory Card International Association spec. Now known as PC Cards.

Phase Shift Keying. In this method of modulation/demodulation, there are two frequencies used (usually 1200 hertz and 2400 hertz). There are 4 different phase angles (0, 90, 180, and 270 degrees), representing dibits 00, 01, 10, and 11. This is usually used for 1200bps transmission. Note that the baud rate using PSK is really 1/2 of the bps rate, since 2 bits are sent at a time instead of one. [See also modulation].

Public Switched Telephone Network. This is the regular phone lines that just about everybody uses.

Aperson who spends a lot of time trying to find out as much as possible about the telephone company [like South Africa's TELKOM], and how it works. They often try to find out ways to make long distance calls for free. Some steal calls from telephone credit card users, some steal calls from the phone company directly, and others don't make "free" long distance calls. They are sometimes confused with hackers.
The program which will create an archive with the extension "ZIP". It is one of the most popular archive programs.

Pulse dialing
A method that some phones use to dial numbers. It involves a series of "clicks." Most modems support this type of dialing, which is the only type available in some remote areas. The other method of dialing is tone dialing.





Radio Link Protocol
Non-transparent data uses a special ensure robust GSM-specific error correction technique called RLP for transmission. Both MTN and Vodacom GSM networks support both techniques.
Regular Pulse Excitation - Long Term Prediction, the speech coding used by GSM
Research and Development in Advanced Communication in Europe.
A modem can be reset. This will change any options (such as parity and speed) to the values that they have when the modem is first used. This can be useful if you change some values for the modem and aren't sure what they do, and then you find that the modem won't work. Resetting the modem will fix everything for you. With Option modems, this is the ATZ command.

This is a normal phone jack. The older South African plugs have a 3-prong connector. All Option modems sold in South Africa have this RJ-11-to-3-prong adapters.

Request To Send. This is when the computer tells the modem that it wants to send information to the other computer. It is only used in half duplex mode. [See also flow control, CTS].



Serial Transmission
A method of transmitting data in which bits are sent sequentially.

Special Interest Group. The GSM MoU has many SIGS.

Subscriber Identity Module. This is a Smart Card installed in every GSM handset. Within the GSM application the three primary roles of the SIM are access control to   the network (authentication & ciphering), service personalisation (SMS, advice of charge, etc.), network branding and advertising (graphics printed on SIM card). The new generation of Phase 2+ SIMs will enable services such as virtual cash, mobile banking, ticket reservations etc.

Short Message Service will display a pager-like 160 character message in the LCD panel on the phone. Your phone must support SMS.

When data is sent continuously, without waiting to make sure there are no errors. Transparent mode on GSM is an example of a streaming method faster than non-transparent mode, but unreliable.



Trunk 1. A heavy duty telephone line.

Trunk 3. A telephone trunk line.

Time Division Multiple Access, the magical technique used by the digital GSM network to squeeze more calls onto one channel by dividing a calling channel into a few "discontinuous" pieces.

This word has no precise definition, but is frequently used. Its definition ranges from "any form of communication over a distance" to "any communication by electric means" to "two computers 'talking' to each other via modems." Methods of communications that probably are considered telecommunications: telephones, cellphones, TV's and fax machines. The word is used both in singular and plural.

The idea of company employees working from home, rather than their office. At home, they can communicate with the office (and other entities) by modem or voice calls.

Telkom (South Africa)
Telkom is the parastatal fixed-line network operator in South Africa. Option modems are approved for use on the telkom network and 25 other networks around the world.

A program which lets you access other computer systems through Internet.

Terminal Emulation
When a communications program can simulate the operations of a smart terminal.

Tone Dialing
This is a method that a phone or modem can use to dial a phone number. It uses one audible tone per digit to be dialed.

Transmit Level
The "loudness" level of the sound leaving a modem to go over the phone lines. It is measured indBm's. It should be different at different frequencies, since certain frequencies have more loss over the phone line than others.
Transparent Data Transmission
A method of transmission in which the transmission medium will not recognize control characters or initiate any control function. Transparent-based phones do not utilise any error correction. Thus the data sent and received MIGHT be corrupted unless a greater than two-bar cellphone signal is used (South African conditions). Non-transparent data uses a special ensure robust GSM-specific error correction technique called RLP for transmission. Both MTN and Vodacom GSM networks support both techniques.




Universal Asynchronous Receiver/Transmitter. This is a device in a computer or modem that will change serial data (the way data comes in over the phone line) to parallel, and vice versa. [See also serial, parallel, 16550 UART, 8250 UART, 16450, 16550 UART].





The ITU standard for fax transmission at 14,400bps.

The international standard, created by ITU, that controls transmission at 300bps.

The international standard for transmission at 1200bps, created by ITU.

The international standard, created by ITU, that controls data transmission at 2400bps.

The ITU protocol for transmission of 1200bps one way, 75bps the other way.

This, combined with V.28 is the ITU standard equivalent to EIA's RS-232C standard. V.24/V.28 has 25 pins, just like the original RS-232C standard.

Part of V.24.

The ITU standard for 9600bps half-duplex communications.

The international standard controlling transmission at 9600bps. It was created by ITU. It has provisions for fallback, if the line is too noisy.

The international standard for 14,400 bps modems, ratified by the ITU.

The international standard for 28,800 bps modems, ratified by the ITU.

A standard error control system created by ITU that is in use on many 9600bps modems and some 2400bps modems. It includes LAPM, as well as MNP 2-4.

V.42 compatible
This is a modem that follows all the V.42 specifications, except for LAPM error control (instead it uses MNP).

V.42 compliant
This is a modem which follows all the V.42 specifications, and uses LAPM error control if possible. Otherwise, it will go to MNP error control.

A ITU standard for data compression. It can compress data with about a 3:1 compression ratio, although it can compressup to 4:1 given the right conditions. Any modem with V.42bis also has V.42 error control. [See also Data Compression].




World Wide Web

World Wide Web. A hypertext system set up on the Internet.

A DOS program to perform UUCICO.

A Windows subroutine library that provides access to the Internet TCP/IP.

The actual file containing Winsock.



This is a packet-switching protocol developed by ITU. It is used to carry large amounts of data at fast speeds over leased phone lines.

This is ITU's 1984 update of X.25, also known as X.25 dialup.

This is the ITU standard protocol for a global system for the exchange of electronic mail.

The ITU standard for a directory of the users of the X.400 system.

A file transfer protocol developed by Ward Christensen around 1977. It is fairly slow by today's standards, but was the first widespread file transfer protocol. It uses blocks of 128 bytes, and after each block is sent, it sends a 1 byte checksum to check for errors. If an error is encountered, the block will be re-sent. Almost every communications program offers this protocol.

The same as Xmodem, but it has a 16-bit CRC instead of the checksum, which makes it more reliable (it catches more errors).

This is similar to Xmodem/CRC, except it uses blocks of 1024 bytes, rather than 128. It is faster than Xmodem, since it needs to stop less often to check for errors. This is sometimes incorrectly called Ymodem. [See also protocol, Xmodem, Ymodem].

The CTRL-S character. This is often used to pause information that is being sent. The information will be continued when an CTRL-Q is received. [See also flow control, Xon].

The CTRL-Q character. This will sometimes continue paused information.

The flow control method using the Xon and Xoff characters. It is built into the software, not the hardware.  






The file extension which refers to archives that were created by the program PKZIP. You need the program PKUNZIP to get the files out of the archive.

A file transfer protocol which is known for its speed, as well as the ability to transfer information about the files which it sends. It has crash recovery and auto-download features, and can use a 32 bit CRC, which makes it almost error-free.



The most common modem format. "8N1" describes the way that your computer and the remote are connected. The first digit is normally 7 or 8, the number of data bits. The second character is a letter describing the parity (N for None, M for Mark, S for Space, O for Odd, and E for Even). The last number is the number of stop bits. Data is sent as follows: Start bit (0) 7 or 8 bits of data (parity bit, if used) stop bit (1) (gap bits, if used)

An ethernet connection that uses UTP (unshielded twisted-pair) wiring.

16550 UART
This is the UART used with most newer computers and high speed modems. There are several variations, but they all include one main feature: they include buffering, so that if data comes in or is sent faster than the computer/modem can accept it, the UART will hold the data (up to 16 bytes) until the computer/modem is ready for it.




Get FREE updates on the latest ringtones,
logos, alerts, mobile news, & free downloads.
Join our newsletter now