Telephony Jargon

Voice over what?

ACD (Automatic Call Distributor):

This is a device that allows for the distribution of incoming calls.


Asymmetric Digital Subscriber Line (ADSL) is a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are not used by a voice telephone call. A splitter - or microfilter - allows a single telephone connection to be used for both ADSL service and voice calls at the same time. Because phone lines vary in quality and were not originally engineered with DSL in mind, it can generally only be used over short distances, typically less than 3mi (5.5 km).


This variant of existing DSL is being rolled out in the UK from April 2008 with every exchange enabled by 2011. The arrival of ADSL2+ is closely linked to work VOIPAR has been doing on its core network, upgrading it to an IP infrastructure in a project known as the 21 century network. ADSL2+ offers speeds of up to 24Mbps, but as it is distance-dependent a lot of people will not actually achieve those kind of speeds.

ATA (Analogue Telephone Adapter):

A device that plugs into a broadband internet connection and regular phone, enabling traditional telephones to make VoIP calls using the internet.


An automated system designed to guide a caller through the options of a voice menu. Typically set to answer and route incoming calls. Call 0800 006 2 006 to hear the VOIPAR Auto Attendant.


The speed at which information passes over the internet.

BRI (Basic rate interface):

Basic rate interface (BRI or ISDN2e) is an Integrated Services Digital Network (ISDN) interface most likely to be found in residential service. This configuration consists of two 64 kbit/s "bearer" channels (B channels) and one 16 kbit/s "data" channel (D channel).


Refers to telecommunication in which a wide band of frequencies is available to transmit information. Because a wide band of frequencies is available, information can be multiplexed (separated) and sent on many different frequencies or channels within one band concurrently, allowing more information to be transmitted in a given amount of time (much as more lanes on a highway allow more cars to travel on it at the same time).


Cable is always on, it is not dependent on the distance you are from the exchange (unlike ADSL) and every person can receive the same speeds - unlike ADSL. The system which is used, or "the protocol", is called DOCSIS (Data Over Cable Service Interface Specification). Currently DOCSIS 1.0 offers speeds up to 38Mbps. The new system, called DOCSIS 3.0, could offer up to 120Mbps and higher. This (D3) is currently in trial at 50Mbps in selected regions of the UK, such as Ashford, Folkestone and Dover.


Centrex is a PBX-like service providing switching at the central office instead of at the customer's premises. Typically, the telephone company owns and manages all the communications equipment and software necessary to implement the Centrex service and then sells various services to the customer. British Telecom markets this service as FeatureLine (although refers to it internally as Centrex)

CDR (Call Detail Record):

Data record typically used to record usage information on a per-call basis. This information might include the incoming DDI, number dialled, start-time, call duration, etc.


Voice encoding/decoding mechanism. Codecs are used to compress the voice signal into data packets.


VoIP uses various compression ratios, the highest approximately 12:1. Compression varies according to available bandwidth.


&Generally refers to the combination of Voice and Data.

CTI (Computer Telephony Integration):

This is technology that integrates the functions of telephones with computers.

DSL (Digital Subscriber Line):

Method of transferring data over regular phone lines. A DSL circuit is much faster than a regular phone connection, and the wires coming into the subscriber's premises are the same (copper) wires used for regular phone service. The phone service is connected to your PC to provide broadband Internet access.


The most commonly used method of connecting LANs. It allows for network communication by using either coaxial or twisted pair cable.


Security software or appliance that sits between the Internet and an individual PC or networked device. Firewalls can intercept traffic before it reaches network routers and switches, or between router/switch and PC, or both. Because the job of firewalls is to prevent access from specific packets over specific network ports, some firewalls must be specially configured to allow VoIP traffic to pass through.

FTP (File Transfer Protocol):

Communicationsprotocol governing the transfer of files from one computer to another over a network.


Foreign eXchange Office interface. The port(s) on a VoIP adapter that connect to an external phone service.


Foreign eXchange Subscriber interface. The port(s) on a VoIP adapter that connect to internal analogue (traditional) phones to enable them to make and receive VoIP calls.


A gateway is basically a protocol converter, i.e. a network point that connects networks using different protocols (tech languages) so that data can be exchanged seamlessly between endpoints. For example, a POTS-to-VoIP Gateway connects the public phone network and packet-switched networks, translating the voice/data into IP packets.

Hosted VoIP:

VOIPAR uses the words "Hosted VoIP" mto describe a Centrex system (see above) whereby we provide a PBX-like service that provides call switching an associated features from our servers, so that our customers only need a VoIP phone at their premises to utilise the telephony features supported by the VOIPAR system..


The use of the internet to make telephone calls, regardless of the device used.

IP (Internet Protocol):

The “language” used to exchange data over the Internet


Every computer or device on the Internet has what is known as an IP address, which uniquely defines that device and enables devices to find each other on the Internet. The IP address format is a string of four numbers, each from 0 to 255, separated by periods, for example,


IP PBX is a phone system on the customer’s site that manages telephones in the enterprise and acts as the “gateway" to external networks (the “switchboard”). Unlike a conventional PBX that requires two separate networks, one each for data and voice, an IP PBX is based on both and can be used with compatible phones.

ISDN (Integrated Services Digital Network):

A type of circuit switched telephone network system in which digital transmission of voice and data passes over regular telephone copper wires.

IVR (Interactive Voice Response, aka Auto-attendant):

An automated system designed to guide a caller through the options of a voice menu.

KBPS (Kilobit Per Second):

A unit of measuring the speed of data transfer – which generally means 1000-bits per second.

LAN (Local Area Network):

A number of connected computers, generally in an office, but also in homes – these machines often share printers and access to file servers.


A traditional phone line which requires a metal wire, or optical fibre cabling to make connections. This differs from mobile lines which make use of airwaves to establish connections.

MAC Address (Media Access Control Address):

An address—typically made up of numbers and letters-- assigned to your hardware that uniquely identifies it’s place on the network.

MBPS (Megabit Per Second):

A unit of measuring the speed of data transfer – which generally means a million-bits per second.

MPLS (Multi Protocol Label Switching):

MPLS is a data-carrying mechanism that belongs to the family of packet-switched networks. MPLS operates at an OSI Model layer that is generally considered to lie between traditional definitions of Layer 2 (data link layer) and Layer 3 (network layer), and thus is often referred to as a "Layer 2.5" protocol. It was designed to provide a unified data-carrying service for both circuit-based clients and packet-switching clients which provide a datagram service model. It can be used to carry many different kinds of traffic, including IP packets, as well as native ATM, SONET, and

OTAP (Over The Air Provisioning):

To configure a mobile device, usually a mobile phone or PDA by sending the configuration settings by text message or a data call Ability


A logically grouped unit of data. The idea with packets is to transmit them over a network so each individual packet can be sent along the most optimal route to its destination. Packets are de-constructed on one end of the communication and re-constructed on the receiving end based on the header addressing information at the front of each packet.


Communication system that chops messages into small packets before sending them. All packets are addressed and coded so they can be recompiled at their destination. Each packet can follow its own path and therefore can work around problematic transmission segments.

PBX (Private Branch Exchange):

In-house telephone switching system that interconnects telephone extensions to each other.

PRI (Primary rate interface):

Primary rate interface (PRI or ISDN30) is an Integrated Services Digital Network (ISDN) interface most likely to be found in business service and is typically used for carrying multiple voice and data transmissions between two physical locations. The Primary Rate Interface consists of 30 B-channels and 1 D-channel using an E1 line. Thus, a Primary Rate Interface user on a E1 line can have up to 2.048 Mbit/s service and uses the Q.931 over the D-channel.

POTS (Plain Old Telephone Service, Post Office Telephone System):

A standard telephone line that VOIPAR handled exclusively before the deregulation of the telephone industry.


Is the set of standard rules for data representation, signalling, authentication, and error detection required to send information over a communications channel.

PSTN (Public Switched Telephone Network):

The network of wires, signals, and switches allowing one phone connect to another anywhere in the world. Some VoIP services provide a gateway from the Internet to the PSTN and vice versa. Read more about PSTN on Wikipedia.

SDSL (Symmetric Digital Subscriber Line):

This is a type of internet connection that allows for faster connection speeds over telephone lines. The distinguishing feature however, is that information travels much the same direction in both directions, hence the symmetry.


“Software” + “Telephone” – basically a desktop program that resembles a handset on your screen, allowing you to make calls with an earpiece or speakers and microphone.

SIP (Session Initiation Protocol):

An ASCII-based protocol that provides telephony services similar to H.323, but is less complex and uses fewer resources. It creates, modifies, and terminates sessions with one or more participants. Such sessions include Internet telephony and multimedia conferences. SIP is a request-response protocol, dealing with requests from clients and responses from servers.

SIP Trunking / IP termination / Call Termination / PSTN Termination

(are the same): SIP Trunking is simply a single conduit pipeline for multimedia elements (voice, video and data). It reduces or eliminates the need for PSTN media gateways as well as reduce or eliminate the need for narrow-band voice circuits. SIP Trunking provides a smart and cost effective solution to customers by eliminating the need to purchase additional equipment, such as managed media gateway devices to interface between IP voice to the PSTN.

TDM (Time-Division Multiplexing):

In its primary form, TDM is used for circuit mode communication with a fixed number of channels and constant bandwidth per channel.


The process of converting or transmitting voice or other signals over a distance, and then re-converting them to an audible sound at the far end.

TCP (Transmission Control Protocol):

The transport layer protocol developed for the ARPA net which comprises layers 4 and 5 of the OSI model. By combining TCP and IP --“TCP/IP” – a connection between two hosts (callers) is made to send messages back and forth.

VOIP (Voice over Internet Protocol):

Voice translated into data and transmitted across an internet connection or network - just like any other file or email you might send. Upon reaching the other end data is transformed back into its original form and emerges like a regular phone call. Read more about VoIP on Wikipedia.

VPN (Virtual Private Network):

A private communications network generally used within enterprises to communicate over a public network using secure protocols.

VDSL (Very High Speed Digital Subscriber Line):

VDSL is deployed over existing copper wiring and, according to BT, can operate at speeds of up to 30Mbps with the chance of getting faster as new flavours of it are deployed. Like ADSL it is still distance-dependent and those closest to the exchange will get the fastest speeds. VDSL cannot be incorporated into the existing telephone exchanges because of interference issues. Second-generation VDSL2 systems could provide data rates exceeding 100 Mbps simultaneously in both the upstream and downstream directions, with the maximum available bit rate achieved at a range of about 300 meters.

WAN (Wide Area Network):

A geographically broad network that uses phone lines, satellites and radio waves to interact. The most commonly recognised WAN is the Internet.

WiFi (Wireless Fidelity):

WiFi is a wireless technology brand owned by the WiFi Alliance intended to improve the interoperability of wireless local area network products based on the IEEE 802.11 standards.

WiFi Mobile :

A mobile phone capable of making both GSM and VoIP calls over a WiFi internet connection.


Wimax stands for Worldwide Interoperability for Microwave Access. It is based on the IEE 802.16 standard, also known as WirelessMAN. In countries with good fixed line infrastructure, WIMAX acts as a filler but in some developing countries is can be the dominant infrastructure for broadband access. Countries such as Pakistan are planning nationwide WIMAX rollouts. It is possible for WiMAX to deliver speeds of up to 70Mbps and operate over distances of up to 50km, although not concurrently.