Telecommunication terminology. Not sure what an abbreviation or telecoms terminology means?  Below is a comprehensive list of commonly used terms but if the one you are looking isnt listed email [email protected] and we will be able to assist you

Account Code A way of attaching an identity to a record of phone call. The code can be used for both incoming and outgoing calls, to indicate the call has be charged to a an account or to indicate the outcome of a call (such as a brochure request). Call Management systems can produce reports listing calls with the same account codes for sales information and it can be made mandatory for a user to enter an account code before a call is made.

ACD Automatic Call Distribution. Allows all incoming calls to be distributed equally amongst a group of people. Typically used in a call centre where agents log in to make or receive calls. ACD systems provide facilities for monitoring the agents performance and the performance of the Call Centre as a whole. An incoming call will be automatically routed to the first available agent (whether an agent has just become free or has been free for the longest amount of time).

ADSL Asymmetric Digital Subscriber Line. High bandwidth network connection for faster data transfer – connection generally allowing more bandwidth downloading than uploading – increases efficiency and reduces costs.

Alpha Tagging The assignment of an alpha-numeric name to a phone extension  – the phone can display the name of the caller rather than the extension number. When an incoming DDI (Direct Dialling Inwards) call is received a name can be shown which relates to the number that was dialled which enables and agent to answer calls in a variety of different ways e.g. using the name of the company or individual calling.

Analogue Device A device that can be attached to an analogue telephone line; telephone, fax machine, cordless phone, answering machine, modem.

ARS Automatic Route Selection. A technique where the telephone system looks at the digits being dialled to make an outside call and automatically routes the call via an alternate route for the most cost effective call.

Auto-Attendant A voicemail feature that allows callers to be automatically transferred to extensions or departments by dialling digits. A tone dialling phone is normally required to do this.

Bandwidth The speed at which a circuit can carry data. The more bandwidth, the faster the data transfer and the lower the costs.

Basic Rate or BRI (Basic Rate Interface) or ISDN2. An ISDN (Integrated Services Digital Network) circuit providing 2 x 64 kbit/sec bearer channels for use by data or speech and one 16 kbit/sec control channel. Two independent calls can be carried at the same time on one BRI circuit.

Battery Back-up please refer to UPS (Uninterruptible Power Supply)

Bell please refer to Loud Ringing Bell.

BLF Busy Lamp Field. Visual indication of the status (busy or not) of lines or extensions through LEDs (Light Emitting Diode).

Bluetooth Wireless communication protocol for several devices to communicate on a common format.

Broadband BT’s brand of ADSL (Asymmetric Digital Subscriber Line).

Bulletin Board An electronic version of a notice board – users can access the bulletin board to obtain information. When applied to voicemail systems it indicates a system of menus that allow the caller to navigate to the information they want, like finding out what films are showing at a cinema.

Call Barring The prevention of calls to certain destinations e.g. overseas calls or calls to premium rate numbers.

Call Forwarding (also known as call diversion). By dialling a code an extension user can divert incoming calls to another destination. The destination may be another extension, a group of extensions, the operator, or an external number like a mobile phone. Different types of diversion are usually possible e.g. diversion of all calls, when busy or on no reply.

Call Logging Data recorded about calls made or received through a telephone system, this data can be used for reporting. Please refer to Call Management and Station Message Detail Recording.

Call Management The use of specialist software to analyse and report on call records which are output from a telephone system and recorded on computer. The results can identify misuse, allocate costs to departments and verify the adequacy of resources.

Call Park A call can be parked by one user and then retrieved by another. Particularly useful when loudspeaker announcements are made e.g. ‘Telephone call for Joe Smith dial 811’. If Joe goes to any phone and dials 811 he will get the call that has been parked there for him.

Carrier Telephone service provider e.g. BT, NTL and Cable & Wireless.

Cat 5 (Category 5) A specification for the transmission performance of a data cable. It is commonly used to describe a building cabling system that allows the user to easily route voice and data circuits to any wall socket. It is designed to be network independent and to allow different computer and telephone systems to co-exist on the same cabling.

CCU Central Control Unit. The box or cabinet housing the central equipment that controls the telephone system.

Centrex A generic name for a feature offered by some Public Network Operators. Users have individual direct exchange lines but calls between them are free of charge and can be transferred. A limited set of features is provided to give something that approximates a virtual telephone system. BT brands for this service are Featureline and Featurenet.

CLI Calling Line Identity is the capture of the caller’s number. There are two types of CLI, a Network CLI is used by network operators to identify the source of the call. It is available whether or not the caller is ex-directory but is never passed on to the called party. The user CLI is passed on to the called party, providing that the caller has not withheld it. By default it is the same as the network CLI but can be changed by the caller’s equipment. For example, a salesperson may want the direct dial number to go out but the MD may want another number to go out instead. CLI is used for the ‘1471’ service where 1471 id dialled to find out who called.  It can also be used to display the number on a phone or computer. CLI is not available on some networks (particularly from overseas) and is usually an optional feature from the network provider as the subscriber has to pay to receive it.

CLIP Calling Line Identity Presentation. A service that provides a called party with the Calling Line ID of the caller. Usually a paid-for option. See also Connected Line Presentation.

CLIR Calling Line Identification Restriction. Would stop the callers own CLI being presented to the called party.

Cloud Based Telephone

Cloud Based Services (Also see hosted)  Data and services such as Microsoft Office, Sage and telephone services are based on servers and equipment away from site and connected via the Internet or “cloud”. Users effectively rent the services from the supplier rather than pay for costly servers and equipment located in the office.

COLP Connected Line Presentation. A service which provides the caller with the identity of the person he has connected to. For example you may dial 01234 567890 but that number may be diverted to another. COLP will provide you with the identity of the person you have actually connected to. The identity is typically the telephone number of the connected party. This is a paid-for service from the network provider and compatible equipment is required to make use of it.

Conferencing The joining together of more than two telephone users in a single call.

Contact Centre A progression of the call centre which merges customer calls with other media likes internet and email in conjunction with CRM applications. A unified approach to customer contact improving customer service levels leading to increased customer acquisition, satisfaction and retention.

Convergence The merging of voice and data hardware solutions like the server based PBX.

CPS Carrier Pre-selection. Uses network access technology, so voice traffic originating from your site will be routed directly to your chosen network with no need for prefix codes. The “selection” of the preferred provider is done automatically at point of entry (the local exchange) to the public voice network.

CRM Customer Relationship Management. A software application to deliver a single view of the customer.

CTI Computer and Telephony Integration. The exchange of information between computers and telephone systems e.g. when a call is received the telephone passes the computer the telephone number of the person calling. This can deliver “Screen Popping” – the presentation of database information based on an incoming caller’s CLI. Information is commonly passed between telephone and computer systems using an Application Program Interface (API) of which the two most common are TAPI (Telephony API) and TSAPI (Telephony System API). CTI is commonly divided into First Party CTI, where a telephone and a computer are directly connected and Third Party CTI, where the telephone system and the computer network communicate through a telephony server, with no direct physical connection between the telephone and the user’s computer.

Custom Service Mode Used in voicemail to indicate a service where the caller hears a menu of choices from which they can choose by pressing buttons on their phone. These choices can transfer the caller to an extension, group of extensions, the operator, leave a message, listen to information,or may offer other menus.

Data Packet A packet is a basic unit of communication over a digital network. A packet is also called a datagram, a segment, a block, a cell or a frame, depending on the protocol. When data has to be transmitted, it is broken down into similar structures of data, which are reassembled to the original data chunk once they reach their destination.

DC5 A signalling system used to communicate between two adjacent pieces of telecommunications equipment e.g. between a telephone system and a router or multiplexer. For communication over longer distances DC5 can be converted to AC15. See AC15.

DDI Direct Dialling Inwards enabling outside callers to call directly to a user’s extension. Normally available on ISDN lines. A business may have 10 lines and 100 telephone numbers and when any of the telephone numbers are dialled by an incoming caller the call is put on to any line that is free. At the same time the dialled number is passed to the telephone system which routes the call to the intended recipient. Typically used to provide direct dial numbers for extension users, fax machines, departments or groups of extensions. Reduces the number of calls that have to be answered and transferred by an operator.

DECT Digital Enhanced Cordless Telephony. A technology that provides greater clarity and smaller handsets for cordless phones. There is a common standard called GAP (General Access Protocol) that allows handsets and base stations from different manufacturers to work together.

Delayed Ringing A feature often used to provide an overflow if the switchboard operator is busy or absent. Incoming calls are sent to the operator but other extensions have delayed ringing, so they will start ringing if the call is not answered after a pre-set time.

Dial up A communications link that connects a terminal and a computer via the Public Switched Telephone Network (PSTN). Differentiated Services (DiffServ)A layer 3 QoS regime that works on a hop-by-hop basis from one end of the data’s journey to the other. This protocol is a common method used by an ISP (Internet Service Provider) to provide quality of service on non-DSL (Digital Subscriber Line) MPLS (Multiprotocol Label Switching) type links i.e. fixed fibre end to end links, based on packet tagging to prioritise time sensitive traffic such as voice.

DISA Direct Inward Station Access. Provides callers with single-digit access to extensions or ring groups.

DPNSS Digital Private Network Signaling System. A protocol to support connection between telecom equipment from different vendors digital equipment. See also QSIG.


DSS Direct Station Selector. A unit that fits alongside a telephone to turn it into an operator console. Typically containing a large number of programmable buttons that can be used to call and to indicate the status of extensions.

DSL Digital Subscriber Line Similar to ADSL, but allows the same amount of bandwidth in both directions.

E+M Another name for DC5.

Extension Lock A facility to prevent unauthorised phone use. An extension can be locked by entering a code and unlocked by entering a password. When locked the phone is subject to call barring, perhaps restricting it to internal and emergency service calls only.

Firewall A firewall is a part of a computer system or network hardware that is designed to block unauthorised access from outside a local area network, whilst allowing authorised communications both in and out. Firewalls can be implemented using either hardware, software or a combination of both.

Gamma A provider of SIP lines, Voip and Hosted telephone platforms, namely Horizon

GAP General Access Protocol see DECT.

Group Ringing A group of extensions is rung by dialling a number. The group may be set as a ring group, in which case all of the extensions ring at once, or it may be set as a Hunt Group, in which case the system will find a free extension in the group to take the call.

GSM Global Satellite Mobile. Improved call security and quality.

GUI Graphical User Interface. A program interface like Microsoft Windows, that takes advantage of the computer’s graphics capabilities to make the program easier to use.

Horizon see Gamma  Hosted Telephone Hosted telephone system

Hosted PBX   This is a service where the call platform and PBX features are hosted at the service provider location ie at a datacentre located off site and connected by the Internet. The business end users connect via IP to the provider for voice service. “Hosted” means to say that the hardware and PBX is hosted at an off-site location from where the VoIP telephone service is being used.

Hunt Groups A means of finding a free extension to take a call. Calls are directed to a Hunt Group and will search for a free extension to take the call. Various hunting types are available, First Free or Terminal Hunting will search for the first free extension in the group, so this person gets most of the calls. Circular or UCD (Uniform Call Distribution) Hunting will share calls equally over the group.

Inter-tel A major manufacturer of business telephone systems, now part of Mitel.

IP Internet Protocol. Access to standard global communications protocol.

IP Address A series of characters that uniquely identifies the terminal equipment which is the origin or destination of data being transmitted.

ISP Internet Service Provider. Allows you to connect to the Internet

ISDN The Integrated Services Digital Network. An internationally agreed method of providing digital communication over the Public Switched Telephone Network (PSTN). Enables the benefits of DDI, CLI, Trunk-to-Trunk Transfer and faster data transfer. See also Basic Rate (ISDN2) and Primary Rate (ISDN30).

ISDN2 see Basic Rate

ISDN30 see Primary Rate

Jitter The measure in milliseconds of the variability over time of the latency across a network. Jitter is a typical problem of the connectionless networks or packet switched networks, due to the data being transmitted being divided into smaller packets, each packet can travel by a different path from the sender to the receiver. Real time communications such as VoIP usually have quality problems due to this effect. In general, it is a problem in slow-speed links or with congestion. See Quality of Service to avoid or solve this issue.

Keyphone A telephone for use with a particular make and model of telephone system which incorporates features allowing it to communicate with the telephone system and display information.

Key System A telephone system designed for all extensions to answer incoming calls. The distribution of all incoming calls across a business or team.

LAN Local Area Network. Enables PCs to communicate data and common devices or servers also connected to the network.

Latency The amount of time measured in milliseconds it takes a packet to travel from source to destination. Together latency and bandwidth define the speed and capacity of a network. The latency of end-to-end data transmission is also known as the delay and too much latency realtime applications such as VoIP will result in packet loss, so parts of the conversation are missing or no conversation is played at all.  See Quality of Service to avoid or solve this issue.

LCD Liquid Crystal Display. A display panel found on many phones capable of showing text prompts or messages

LED Light Emitting Diode. A semi-conductor device used as an indicator lamp. Typically these are incorporated into buttons allowing visual indication of calls, voicemail messages and status of other lines and extensions.

LCR Least Cost Routing. A technique where the telephone system modifies the digits dialled by a user making an outside call in order to route the call via a low-cost carrier. Typically the routing decision is based on the number dialled and it is possible to have several carriers configured on the same telephone system to take advantage of the cheapest route to any destination. See also Automatic Route Selection (ARS). Typically ARS incorporates and builds on the capabilities of LCR (Lease Cost Routing).

Live Call Screening A facility available on some voicemail systems which allows someone who has diverted calls to voicemail to listen to a caller leaving a message and pick up the call if he wants to.

Loud Ringing Bell An audio warning device to alert someone that a call is ringing. It may simply be an extension bell to a telephone or it could be a set of bells around the building so that anyone can pick up the incoming call.

Packet Loss Occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss can be caused by hardware failure, faulty network cabling/patch leads or ISP (Internet Service Provider) network performance. Packet Loss can also occur when data arrives too late to be processed in terms of a realtime application. For example, for a VoIP call to be heard and played in realtime, if the delay is too long between the voice being sent and received, the data packets containing parts of the conversation arriving too late will be dropped. See Latency and Jitter.

Mailbox A reference to the location where voicemail messages for a particular user are stored.

MAPI Microsoft Application Protocol Interface. Protocol designed to ensure all Microsoft applications can communicate with other applications in a standard and documented format.

Meter Pulse Detection (MPD) A BT service for their analogue lines, to allow a subscriber to accurately establish the charge of a telephone call.

Mitel A major manufacturer of business telephone systems.

MSN Multiple Subscriber Numbering. An optional feature of ISDN2 lines allowing up to 10 telephone numbers to be assigned to a single line so that devices connected to that line can be called individually. Can be used to produce a limited version of DDI.

Multiprotocol Label Switching (MPLS) A layer 3 technology implemented by Internet Service Network Providers by MPLS labels being added to the packet header.  The network makes decisions on routing at each hop based on the MPLS label rather than examining the packet itself, which enables much faster and more efficient routing end to end applying prioritisation to different types of traffic like voice.

Music on Hold An audio signal that is played to a caller on hold to reassure him that he has not been cut off.

Network The equipment and transmission facilities for communication between computer systems.

NEC Manufacturer of telecoms systems

Network Hub A computer networking device that connects devices together to create a local area network for data to be sent and received between all devices connected. A hub does not have software loaded to ensure data traffic is routed intelligently so its use in networks is now limited as it creates network congestion and latency as it broadcasts any traffic transmitted by any device to all other ports.

Network Switch A network switch is an intelligent computer networking device that connects devices together, along with additional network switches, to create a local area network for data to be sent and received between all devices connected. Most common types installed are layer 2 and layer 3 which is commonly referred to the network switches ability to route data between devices, either at layer 2 using physical MAC address or at layer 3, using logical IP addressing.

Night Service Most telephone systems have at least two operating modes, Day Service and Night Service. These are typically used to route incoming calls to a different destination and to apply call barring to prevent unauthorised use of the phones by security or cleaning staff.

Overflow Group see Delayed Ringing.

Panasonic . A telephone equipment manufacturer

Parallel Port Port in a PC used for the connection of external equipment like a printer or scanner. See also serial port.

Patch Panel Cabling connection point. This is typically the part of a structured network cabling system (cat 5) that enables switching of services either voice or data to RJ45 sockets.PBX/PABX Private Branch Exchange/Private Automated Branch Exchange. Allows central control of incoming calls via a single operator

PMS Property Management System. Hotel ‘Front of House’ software package.

POT Plain Ordinary Telephone. Used to distinguish an ordinary analogue telephone from a keyphone. Also known as an SLT (single Line Telephone)

PRI Primary Rate Interface see Primary Rate

Primary Rate An ISDN circuit providing (in Europe) up to 30 x 64 kbit/sec bearer channels for use by data or speech and two 16 kbit/sec control channels. Up to 30 independent calls can be carried at the same time on one Primary Rate.

PSTN Public Switched Telephone Network. Everyone connected to standard communications platform.

Pulse Dialling Also known as LD (Loop-Disconnect) dialling. A method of dialling where the telephone is alternately disconnected and connected to signal to the exchange. For example if a digit 5 is dialled this could be signalled by sending 5 disconnection pulses. The frequency and length of the pulses and the number of pulses for each digit can vary from country to country. This dialling method is now mostly superseded by tone dialling.

Quality of Service (QoS) The ability to provide different priority to different applications, users or data types to guarantee a certain level of performance for Local Area Networks and Wide Area Networks. Essential for real time applications such as VoIP or Video transmission. Most common method deployed on LAN’s today is VLAN. Dependant on the type of public connection being used (the Internet, fixed lease lines etc.)Wide Area Networks usually deploy Bandwidth Management to reserve levels of bandwidth for certain types of traffic or MPLS/Differentiated Services data packet tagging where end-to-end QoS can be applied.

QSIG Q Signalling Standard. A standard dial up protocol designed to give feature transparency between systems at different sites across the PSTN. Allows products from different vendors to work together. See also DPNSS.

Router Routes data traffic and can be used to connect LANs together or as a single connection point between a LAN and an ISP.

SBUS The digital connection from a telephone system to a PC. Provides the ability to utilise ISDN lines for voice and data traffic.

Screen Popping The initialising and presentation of database information selected using the CLI. Reduces the time spent searching for customer information

Serial Port Port in a PC used for the connection of external equipment and also used for connection of call-logging, CTI, etc. See also parallel port.

SIP Session Initiation Protocol. A protocol for communicating data that is set to be the common protocol for sending Voice over IP traffic. SIP trunks are commonly used for the simple porting of numbers allowing more flexibility.

SIP Trunk A SIP Trunk is a facility provided by specific ISP providers that allow the placing of out-bound calls and the receiving of inbound calls using an internet DSL connection and a router connected to the customers LAN, rather than using dedicated traditional ISDN or analogue lines.

SLT Single Line Telephone. See POT.

 SL 2100 , SL1100 an NEC telephone system

SMDR Station Message Detail Recording. See Call Logging.

SV 8100 , SV 9100 an NEC telephone system

Switch See PBX/PABX.

TAPI Telephony Application Program Interface. A standard devised by Microsoft Corporation for communication between a computer terminal (workstation) and a telephone extension. There are several versions of the TAPI standard and various options within the standard so it should not be assumed that all the features of one TAPI compliant device will be available on any other TAPI compliant device. See also TSAPI.

TCP/IP Transmission Control Protocol/Internet Protocol. Set of layered protocols that enable shared applications among PCs in a high speed communications environment.

TDM Time Division Multiplexing. Traditional telephony technology employed to connect two parties in a call via a PBX.

Tone Dialling Also known as MF (Multi-Frequency) or DTMF (Dual Tone Multi-Frequency). A dialling method which generates audio tones when digits are dialled. These tones are sent down the line and can be detected by telephone systems or other devices.

Trunk A telephone exchange line to receive and make calls.

Trunk-to-Trunk Transfer A facility which allows an incoming call received on one line to be transferred to another line i.e. both callers are external to the telephone system. Typical uses include transferring an incoming caller to someone’s mobile phone.

TSAPI Telephony System Application Program Interface. A standard devised by Novell Corporation for communication between a network server and a telephone exchange. Because it is working at a system level this offers more flexibility than TAPI but is also more complex to implement.

Two-Way Record A facility of voicemail systems and answering machines which allows both sides of a telephone conversation to be recorded for later playback.

Unified Messaging A messaging platform that allows management of voice, fax and email from a single user interface (PC). Improves efficiency as all messages are presented from the one place to the user.

UPS Uninterruptible Power Supply. Provides continuous power source to the telephone system in the event of a mains power fail. Also referred to as Battery Back-up.

UTP Unshielded Twisted Pair. A type of cable commonly and imprecisely used to differentiate from computer cables using co-axial cable such as 10 Base 2, Thin Ethernet, Thinnet, Thick Ethernet, Thin Ethernet or IBM Twinax.

Video Conferencing Multi-subscriber video calls generally using an IP solution.


VLAN A virtual LANA group of IP devices with a common set of requirements that communicate as if they were attached to the same broadcast domain, regardless of their physical location. A VLAN has the same attributes as a physical LAN, but it allows for end stations to be grouped together even if they are not located on the same network switch. Essential to provide Quality of Service (QoS) to a network to ensure that VoIP calls, or other mission critical real time data traffic types, are prioritised over other standard data traffic to ensure successful transmission.

Voicemail A voicemail system typically provides a central “answering machine” for users of a telephone system. The user diverts his calls to the voicemail system, which will play a personalised message to a caller and allow them to leave a message for the extension user. Most voicemail systems also provide options for routing callers to departments or extensions and for giving out information to callers.

VOIP Voice Over Internet Protocol. Allows voice calls to be switched over any data carrying network reducing fixed infrastructure costs.

VPN Virtual Private Network. Provides users with inter-site communications or allows remote offices to be connected together across the internet, which could be implemented over fixed LAN-to-LAN VPN circuit connections using routers but also via dial up software VPN connection. This has many cost benefits to the user as the need for fixed line voice circuits may be removed. Essential for remote workers of offices to connect back to a main office to share applications, resources and also offers support for VoIP calls via the office PBX communications platform.


Yealink Manufacturers of IP telephones and IP telephone systems 

WAN Wide Area Network. Improves cost and efficiency as PC users in different sites may all access the same information as if they were all connected locally on the one local area network.

WAP Wireless Access Protocol. A means of accessing the Internet using a mobile phone.

WiFi A means of connecting to an Internet or data service wirelesly rather than plugging a cable in.

WOC Windows Operator Console. PC based operator terminal. Allows the user to see the status of lines and extensions on their PC screen and answer and transfer calls with the click of a mouse.

XDP Extra Device Port.  Analogue port in the back of some keysets, which can be used as either a ‘double’ of the existing extension number (i.e. for an analogue DECT) or as a totally different extension number (i.e. for an analogue modem.