A.7 Telecommunications Glossary

- A -

Access
Sometimes known as "Local Loop", access is the provision of connectivity between the subscriber telephone terminal and the local exchange.

Asymmetric Digital Subscriber Line (ADSL)
ADSL allows very high-speed data movement over regular copper telephone lines. The term is "asymmetric" because the speeds going INTO your house or business are much greater than the speeds sent from you back up the line. Operating in this "unbalanced" way makes sense because the large files requiring a lot of speed and bandwidth are coming TO your computer screen, while all that's being sent back from you is a relatively small amount of data -- the signal you send back down the line when you click your mouse or type on your keyboard.

Amplifier
A device used to increase the strength of electronic signals.

Analogue Transmission
A form of transmitting information characterized by continuously variable quantities as opposed to digital transmission, which is characterised by a series of discrete numbers. All telephone companies support a minimum analogue data speed over phone lines. If your community telephone exchange has "analogue switching equipment", then you do not have access to the new communication technologies. See also "digital" and "modem."

Antenna
The device that concentrates a beam of electromagnetic waves to a focal point so as to send/receive signals.

Aperture
The effective cross-sectional area of the antenna. The larger the aperture, the stronger the signal the antenna receives or transmits.

Asynchronous transfer mode (ATM)
"Asynchronous" is a fancy word for "same." ATM is a switching technology that allows voice, data and video information to be moved over the same (asynchronous) communications network.

- B -

Backbone
The main line that ties networks, phone systems or computers together. It's like the human skeleton, with many small connections (called nodes or terminals), branching off from the backbone.

Bandwidth
A way of measuring how much information flows through a line over a unit of time. Bandwidth can be measured in various ways such as the number of bits transmitted per second (See bit rate). The range of frequencies, expressed in Hz that can pass over a given transmission channel. The bandwidth determines the rate at which information can be transmitted through the medium.

Baud, baud rate
How transmission speed (bandwidth) is measured in the digital world. Bits per second (bps) in a binary (two-state) telecommunications transmission.

Binary
Numbering system having only digits, typically 0 and 1

Bit
The smallest single unit of information (either a 1 or 0 in a binary system).

Bit rate
The speed at which bits are transmitted usually expressed in bits per second (bps).

Bridge
A telecommunications "bridge" is used to connect several telephone circuits (for conference calls) or to link up computer networks

Broadband Channel
A communication channel, such as microwave, coaxial cable, satellite, or fibre optics, that transmits data at rates of megabits (million bits) per second or higher.

Bypass
Establishing communications link without using facilities of the local carrier (PTT).

Byte
In most computer systems, one byte = eight bits. A byte is the memory space needed to store one letter of the alphabet.

• kilobyte (KB) = about a thousand bytes (1,024 bytes)
• megabyte (MB, or "megs") = about a million bytes (1,048,576 bytes)
• gigabytes (GB, or "gigs") = 1,000 megabytes

- C -

C-band
Refers to the frequency in the 4 GHz to 6 GHz range. It is susceptible to terrestrial microwave interference, which is a particular problem in cities and urban areas of world-wide coverage, and is less susceptible to rain and weather fades, than Ku-band. Typically used for DTH and telecommunications.

Cable
In the world of telephone companies, a cable is one or more insulated wires inside a common protective wrapper. Don't confuse this with coaxial cable, a special form of cable used by cable television firms. Coaxial cable is made up of one or more tubes, each of which has a wire inside (and thus insulated from) other wires around it. This makes it possible to run many more circuits through a coaxial cable using a system called "multiplexing." (See multiplexing)

Capacity
The maximum amount of traffic that a circuit or circuit group can handle.

C-Band
The designation for satellite communications operating at 6 Ghz (billion cycles per second) uplink and 4 Ghz downlink. These frequencies are also used for terrestrial Microwave.

CCITT
International Consultative Committee for Telegraphy and Telephony; a committee established by the International Telecommunication Union.

CDMA
Code Division Multiple Access (CDMA) is a cellular phone standard popular in North America.

Cellular
A mobile telephone system that uses radio waves to provide coverage in certain geographic areas or "cells". These cells are usually adjacent to each other and combine to offer continuous coverage over wide areas such as entire cities or highway corridors.

Central office switching centre
The place where your phone line is linked up with all the other phone lines in your area, and out to the rest of the world.

Channel
An electrical transmission path between two or more stations. Channels may be furnished by wire, radio, fibre or a combination of all three.

Circuit
A physical transmission path between two or more points. (See channel)

Common Carrier
Usually a company that owns a transmission medium and rents, leases or sells portions for a set tariff.

Communications satellite
A device sent up into space used to relay telecommunications signals between two or more points. The main advantage of satellites is the relatively low cost of the earth station equipment needed to link up with satellites compared to stringing wire or fibre optic cable over very long distances.

Connectivity
Capability of exchanging data between telecommunications devices.

Convergence
The mixing together of television, computer, telephone, radio, cable and wireless technologies. Through digital technology voice, image and sound can be reduced to digital "bits" and sent over any kind of access line.

Coverage (Footprint)
The area on earth capable of effectively receiving satellite transmission.

Crossbar
Electro-mechanical exchange system in which connections are made by actuating bars in a crossing matrix.

- D -

DCE
A device that establishes, maintains, and terminates a session on a network. It may also convert signals for transmission.

Dedicated access line
A direct, permanent connection between a phone or computer and something else outside. For example, a branch office might have a dedicated access line to the company's head office, for phone calls, data, or both.

Demodulation, demodulator
Demodulation converts data back and forth between digital and analogue. A demodulator is the technology that does this. (See modulation, modem.)

Digital
The form of electronic processing and transmission in which all information, including analogue waveforms and control data, is converted to binary format.

Digital compression
Techniques used to compress digital signals to allow transmission within a much smaller bandwidth.

Digital Signal
A electrical signal carrying information by means of variations in its duration and amplitude.

Digital switched network (DSN)
A high-speed digital switched public network which allows access to a wide range of services such as telecommuting, videoconferencing, telemedicine, distance education and criminal identification at prevailing long distance rates and discounts. (See also Integrated Services Digital Network, or ISDN)

Digital transmission
A system for sending information over access lines where sound waves and other information are transmitted in a series of on and off pulses, or beeps. This type of transmission is sharper, clearer and quieter than analogue transmission. (See analogue)

Digitize
The way to convert analogue signals to digital form.

Double Hop
Information that is passed from terminal to terminal in two stages - from terminal to hub to terminal, via a satellite link. (Terminals in a star configuration can communicate with each other only in this manner).

Downlink
The retransmission of a signal from a satellite transponder down to the earth stations.

Duplex Transmission
Simultaneous two-way (transmit and receive) independent transmission.

- E -

Earth station
The antennas, receivers, transmitters and other equipment needed on the ground to transmit and receive satellite communications signals.

EDS
Electronic Data Systems.

Erlang
Standard measure of telecommunications traffic.

Encoding/Decoding
The process of organising information into a format suitable for transmission, and then reconverting it upon reception.

Exchange
A basic unit for the administration of telephone service, which generally includes everyone in one town plus adjacent areas. There can be more than one exchange within a larger town or city. The territory served by an exchange, within which local rates apply, is known as the exchange area or local service area.

- F -

Fibre Optics
Glass strands through which light transmits telecommunications signals.

Fibre optics transmission system (FOTS)
A system which uses glass fibres the size of human hairs through which light is transmitted. By changing the patterns of light sent through the lines, information is transmitted. These signals are read by light-sensitive devices. Fibre optics generally allow for a much greater speed and bandwidth than transmitting over regular wires, microwave or satellite.

Final mile
Communications systems required to get from the earth station to the point at which the information or program is to be received and used.

First Mile of Connectivity
phrase that reverses traditional thinking that sees rural areas as being at the "last mile" of telecommunication connectivity.

Footprint
The geographical area covered by a particular satellite. See coverage.

Frame relay
A high-speed data service.

Frequency
The number of times a complete electromagnetic wave cycle occurs in a fixed unit of time, usually one second.

Frequency Modulation
Technique by which a radio wave's frequency is varied (modulated) so it can carry a signal.

- G -

Gateway
Device that interconnects networks running incompatible communication protocols. It translates one set of protocols to another.

General Tariff
The official published rates and rules provided by a telecommunications common carrier.

Geostationary (Geosynchronous) orbit
A method of keeping a satellite parked over the same spot on earth all the time. The satellite is put into an orbit so it travels around the earth at the same speed as the earth is turning on its axis. From earth, the satellite thus appears to be parked.

Most communications satellites are in an orbit 22,300 miles (35,800 Km) over the equator. The main uses of GEO satellites are: signal relays for broadcast, cable and direct TV; meteorology; intelligence operations; mobile maritime telephony.

GSM
Global System for Mobile Communication (GSM) is a cellular telephone standard created in Scandinavia in 1992 (www.gsmworld.com)

- H -

Hardware
Electrical and mechanical equipment used in telecommunications and computer systems.

HDTV
High density TV. A new standard designed to replace the NTSC (National Television Standards Committee) standard by the year 2005.

High gain antenna
An antenna that improves the efficiency of signal reception, a high gain antenna is commonly used to improve signal reception in areas at the fringes of the electro-magnetic waves transmitted from a wireless tower.

High speed
Refers to data communications systems operating at speeds above 9,600 bits per second. (See low speed; medium speed)

Hub
The master Earth station in the VSAT network.

Hertz (Hz)
The basic measure of frequency with which an electromagnetic wave completes a full cycle from its positive to its negative pole and back again. Each unit is equal to one cycle per second. KHz, MHz, GHz (1 thousand, 1 million and 1 billion cycles per second respectively).

- I -

IDN
Integrated Digital Network: exchange and inter-exchange network configuration in which all plant in path of a call is digital and digital technical processes are integrated end-to-end.

Integrated Services Digital Network (ISDN)
A telecommunications service that links you directly to the telephone company's digital network. With ISDN, your access line is fully digital. In other words, ISDN provides a completely digital link making possible the simultaneous, high-speed transmission of voice, data, still image and video signals over a single telephone line.

Interface
Devices that operate at a common boundary of adjacent components or systems and that enable these components or systems to interchange information.

International Telecommunications Union (ITU)
An organisation set up to promote world-wide standards and the development of linked networks throughout the world. Without the ITU, it would not be possible to make phone calls between continents. (www.itu.org)

Intertoll trunk
A line linking the switching offices of different telephone exchanges used to route long distance calls.

- K -

Ka-band

Refers to the frequency in the 20-30 GHz range. The Ka-band will allow the use of terminals with even smaller antennas than Ku-band. Spectrum availability is also significant. Ka-band satellites will operate like a telephone network, supporting broadband and narrowband applications.

Kbps
Kilobits per second. Refers to transmission speed of 1000 bits per second. (See byte)

Ku-band
Refers to the frequency in the 12 GHz to 14 GHz range. Can support data, video, and voice with smaller dishes than C-band. More susceptible than C-band to problems arising from atmospheric conditions such as rain fade, but less susceptible to terrestrial microwave interface. Typically used for DBS (Direct Broadcast Satellite) TV, but increasingly for high-bandwidth Internet and data services.

- L -

LAN (see Local area network)

L-band
The frequency range between 0.39-1.55 GHz, also known as the 1.5GHz band. Typically used for Digital Audio Broadcasting (DAB).

Leased line
A telecommunications channel leased between two or more points at a flat monthly rate. Also called dedicated or private line

Line
A communications channel. Also called a circuit, trunk or facility. It often refers to access to the public switched telephone network (e.g., residence line, individual business line).

Local area network (LAN)
A way of connecting several computers together that are located close to each other, either in the same room or building, so that they can share files through a server and share devices like printers and copiers.

Local exchange carrier
Your local telephone company -- the one that provides you with access lines.

Local loop
A line connecting you to your local phone company's central office/switching centre.

Local Multipoint Communication Systems (LMCS)
A wireless service capable of carrying basic and advanced communication services such as "wireless" cable TV, high speed Internet access, video conferencing and various other multimedia programming. Present LMCS technology operates within a 4-5 km radius but relay points can be set up to cover wider areas. In an LMCS community, homes and businesses send and receive the signals through small, unobtrusive antennae plus the associated electronics that are about the size of a shoebox.

Low Earth Orbit (LEO)
Satellites in an orbit 100 to 1,000 miles above the earth. LEO Satellites are used mainly for communications, spying and remote sensing. The smallest LEOs are used mostly for data communication. Big LEOs carry the world-wide mobile phone network. Broadband LEOs offer high-speed, high-bandwidth data communications such as videoconferencing.

- M -

Microterminal
Another name for VSAT.

Middle Earth Orbit
Satellites at an orbit of 1,000 to 22,300 miles, used mainly for GPS (Global Positioning System) types of surface-navigation systems. MEO will soon host four new constellations of voice and data satellites.

Microwave transmission system
A high-capacity transmission system that sends information using high-frequency radio signals called microwaves. Originally, microwave systems offered only analogue transmission. Today, microwave systems are commonly digital.

Modem
Computers generate data in digital form. To send this digital stuff over an analogue phone line, the data has to be converted. A modem does this. Literally, "mo-dem" is a contracted form of the words "modulate-demodulate" because it is converting (modulating) data back and forth between analogue and digital formats.

Multiplexing
Techniques that allow a number of simultaneous transmissions over a single circuit so as to accommodate multiple users or uses.

Multipoint
A line or channel connecting more than two specific service points.

Multimedia
Technology that employs several types of media such as video, audio or data, or several different media components such as videotape and laser disk players, computers or video cameras, in a single presentation.

- N -

Network
Circuit over which computers or other devices may be connected with one another.

NTSC
National Television Standard Committee: TV transmission standard used in America and parts of Asia.

- O -

Optical fibre
See fibre optics

- P -

PBX
A private telephone switch that establishes voice-grade circuits over tie-lines between individual users and the switched telephone network.

PCO
Public Call(ing) Office: a commercial location for making telephone calls. PCOs are very common in developing countries where few people own private telephone lines.

Packet
A group of digital bits put together in a bundle or packet to make transmission faster. One little packet includes not only your data (such as what you type on your computer screen) but also control information such as a source and destination address and an identification number.

Packet Switching
Technique where bit grouped packets are specifically routed to their destinations based on the availability of transmission paths.

Personal communications services (PCS) or personal digital phones
This is a wireless technology, which offers an alternative to cellular phones. The digital phones are small (about the size of a pack of cigarettes) and offer many of the features that regular wired telephones users enjoy such as call display, call forward, E-mail, faxing etc.

Point-to-Multipoint (PMP)
A type of subscriber radio system in which a number of outlying localities within line-of-sight of a single station or repeater can be connected into the telephone network at one central point. The central station is usually co-located or directly connected with the exchange and thus provides the technical network interface between the remote subscribes and the telephone exchange service. This system is commonly used in rural areas to connect widely dispersed subscribers into the network.

Pots
Jargon for "plain old telephone service."

Protocol
A formal set of conventions governing how communication systems can talk to each other.

Publicly switched telephone network (PSTN)
The world-wide dial-up telephone network or a portion of that network. Whatever system you own should be linked somehow to the PSTN so you can make long distance phone calls, or go on the Internet.

Pulse Code Modulation (PCM)
A common form of encoding and transmission in which analogue speech signals are converted to digital format for the purpose of multiplexing and transmission over distance. PCM is commonly used in multi-circuit inter-exchange trunk system, or "subscriber carrier" systems in which a number of telephone subscribers along a route are served from the same cable.

- R -

RAN
Rural Area Network

Router
A specialised switching device to link geographically separated local area networks and computer systems.

Remote Switching Unit (RSU)
An extension of a larger digital telephone exchange, in which a number of telephone lines (in groups of up to 256) can be located remotely from the main exchange and connected via a transmission system.

RTB
Rural Telephone Bank

- S -

Satellite
An orbiting system in space that receives radio Communications signals from earth stations on earth and then retransmits them to earth stations at distant locations.

Signal
The combination of waves that travel along a transmission channel and act on the receiving unit.

Softside of Telecommmunications
There's more to telecommunications than satellites, computers and telephones. As communities gain access to new information and communication technologies, it is important that they are trained to use, operate and manage the systems. It is equally important that ICTs are applied to the benefit of the community - for education, economic development, telemedicine, human rights, etc. Programs that support the human side of telecommunications are sometimes referred to as the softside of telecommunications.

Spectrum Coordination
Coordination of the frequencies utilised by various users so as not to interfere with each other.

Strowger
Early automatic telephone switching system using selectors which rotate directly under dial or other pulses.

- T -

T1 Carrier
A time division multiplexing system for carrying digital voice and data at approximately 1.544 Mbps.

TDMA
Time Division Multiple Access is a cellular telephone standard popular in North America.

Telecentre
Also known as Multimedia Centre, Public Calling Centre (see PCO), or Community Access Centre. A public location where people can access communication tools. An evolving phenomenon.

Telecommunications
The transmission or reception of signs, signals, images, sound or intelligence of any kind over wires, by radio waves, or other technical system.

Telecommuting
Use of computer and telecommunications to enable people to work at home.

Teledensity
The number of telephones or telephone lines per 100 population.

Teledesic
Teledesic is preparing to launch a global, broadband "Internet-in-the-Sky." A constellation of 288 low-Earth-orbit satellites are expected to provide affordable, world-wide, "fibre-like" access to telecommunications services such as broadband Internet access, videoconferencing, high-quality voice and other digital data needs - everywhere on the planet. (www.teledesic.com)

Telephone
A device often taken for granted if you have easy access to the use of one. Used mostly for voice communications. A telephone takes sound and converts it into electrical waves, which can then be sent over communications channels.

Throughput
The aggregate user data carried by the channel during a specified time period. Expressed in bps or packets per second.

Tollcarriers
Companies that provide long distance services.

Transmission system
What you need to move information from one location to another. This could be copper wire, fibre optic lines, or radio waves.

Transponder
An electronic device on a satellite used to boost or amplify signals before sending them back to earth. The transponder receives an uplink signal at one frequency, converts its frequency, amplifies it, and retransmits it to the ground. Satellites generally have 10 - 40 transponders.

Trunk
Transmission path and main network cable that serves as a common artery between switching units, central offices or data-concentration devices.

- U -

Universal Intelligent Communication Network (UICN)
Future concept of telecommunications network wholly controlled by artificial intelligence.

Uplink
The transmission of signals from an earth station to a satellite.

- V -

VSAT
Very Small Aperture Terminal. An earth station with a small antenna of usually 0.9-1.8 metre (3 - 6 foot) diameter. Typically used in point-to-multipoint data networks.

Voice Coder
Modulator that translates the analogue (voice) signal into a digital signal.

Voice Mail
A voice messaging system in which spoken messages are recorded for later play back or transfer to others.

- W -

Wide area network (WAN)
A network which links computer systems together over a wide area, such as between different towns or provinces. Similar in purpose to LANs (local area networks) which allow files to be shared and data transferred over shorter distances

Wired telephone service
Basic telephone service using wires. This wireline is often called the "local loop" or "twisted pair."

Wireless communication
Sending signals without a physical connection using technologies such as cordless telephones, cellular telephones or microwaves.

Wireless Local Loop (WLL)
Systems that use wireless technology (radio) to connect subscribers to the local telephone exchange. The vast majority of the world's exchange service customers are connected via dedicated copper wire. WLL is a cost-effective solution in developing countries where meeting basic service demand through build-out of the wire network would take much longer to achieve.

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