Asynchronous Digital Subscriber Line is a type of digital subscriber line which offers two different data transfer speeds depending on whether you are transmitting or receiving data. ADSL offers faster download speeds than upload speeds and takes advantage of the fact that Internet users receive more data from the Internet than they transmit.


When internet access is by dial up, the connection is only in place when the user actually dials into the network. xDSL are fast internet access products which are always connected to the internet once the computer and modem are turned on. They are said to be "always-on".


Refers to a signal which can take every value within a particular range. When we speak our voice produces frequencies and loudness levels which can take any value within a range of values. For example, the range of values loudness can take is a function of how loud or quiet we can speak.


Backhaul is an industry term used to describe how data is transmitted from a regional centre back to the centre of the telecommunications or data network. For example, to connect an e|net customer in Cork to one in Galway the data passes from the Cork MAN and is connected over backhaul links to Galway. These backhaul links are provided by other telecommunications operators.


Describes the capacity of a digital channel expressed in bits per second (bps). This is also referred to as the speed of the connection. A bandwidth of 64kbs is required to transmit a normal voice telephone conversation.


A bit is an information unit used in computing and information theory and is the smallest unit of storage currently used in these fields. A single bit (short for binary digit) is a 0 or a 1, or a true or a false, or for that matter any two mutually exclusive states.


A general term referring to access data rates - usually greater than 2Mbs (megabits per second).


A byte is a collection of bits, originally variable in size but now usually eight bits in length.


Co-Lo is an abbreviation of Co-Location and refers to a location on the Metropolitan Area Network where operators can site telecommunications and data equipment.

Dark Fibre

Dark Fibre describes fibre through which no light is transmitted. It is installed fibre cable that is not carrying a signal.


Technical term referring to the information we wish to transmit across a network.


Refers to a signal which can only take certain values within a range. The simplest example is that of a binary signal which can only take a value of 0 or 1. Digital signals are used in the majority of voice and data networks currently deployed.


The ability to provide a backup service in the event of disruption or breakdown. In a fibre network this is normally achieved by placing an end user on a ring of fibre. This means if one side of the ring is broken, data can continue to be transmitted through the second undamaged fibre.


Digital Subscriber Line is a technology that has the ability to move data over traditional copper telephone lines at speeds of up to 6 million bits per second. However the speed is dependent on the distance of the customer from the operator.


Duct is the term for a pipe installed underground into which fibre optic cable is installed.


Ethernet is a packet-based computer networking technology for local area networks (LANs).


FTTB is an abbreviation of the phrase "fibre to the business".


FTTH is an abbreviation of the phrase "fibre to the home".


A term to describe how operators connect their networks together.


Information and Communication Technologies is an umbrella term that covers all advanced technologies in manipulating and communicating information.


Internet Protocol - describes the technology which permits users to transmit and receive data across the Internet.


Describes the location where fibre optic cables are jointed or spliced together.


Kilobits per second - describes the speed of a connection i.e. one thousand bits of data per second.


Local Area Network - a network connecting computers within a building or campus, normally using Ethernet technology.


Metropolitan Area Network - a transmission network built within a metropolitan or city.


Megabits per second - describes the speed of a connection i.e. one million bits of data per second.


Modulator - Demodulator - a piece of equipment which modifies a signal so that it is suitable to be transmitted down a communication link. In the case of a home PC connecting to the internet using a dial-up connection, the Modem translates the digital signal from the PC into an analogue signal suitable for transmission down the copper pair to the telephone exchange.

Multi Mode Fibre

Multi-Mode fibres are designed to allow light to be transmitted in the different modes. These different modes means that information arrives at different times, resulting in dispersion of the transmitted signal.


Network Operations Centre - a location where technical staff are present using computers to monitor and control a voice or data network.

Optic Fibre

Optic fibre or fibre is a medium used to transmit data and is made of very pure glass. Unlike copper which transmits electrical signals, the data is transmitted down the fibre in the form of modulated light using special lasers.

Optic Fibre Pairs

A pair of fibres is required in a network, one pair to transmit data and another to receive data.


Point of Presence. A location where operator’s site equipment on the edge of their network close to the end user.


The ability to provide a backup service in the event of disruption or breakdown. In a fibre network this is normally achieved by placing an end user on a ring of fibre. This means if one side of the ring is broken data can continue to be transmitted through the second undamaged fibre.


Synchronous Digital Hierarchy - a data transmission technology providing high data transfer speeds i.e. the minimum transmission speed is 155Mbs.

Single Mode

Fibres used for long-distance communication are known as single mode fibres, as they have only one strong propagation mode.


Phrase used to describe how fibres are connected together in joints. The maximum practical single length of fibre is about 2,000 metres so joints and splices are required to build a fibre optic network.


Phrase used to describe a fiber-optic network connection to an end user which does not have resilience or diversity. This normally means that the fibre entering and leaving the customer's premises is placed in the same duct and follows the same route to and from the network. If the fibre in the Spur is broken then the end user no longer has access to the network.


Describes tubes inserted into ducts through which fiber-optic cable is run.


Term used to describe speech communication over a network.


A method of delivering voice services across the Internet or other data networks.


xDSL is a term used to describe the different types of digital subscriber line technology currently available e.g. SDSL, HDSL, VDSL and ADSL.