Glossary of Terms

Decoding those tricky telecommunications acronyms

Not sure what some of the acronyms on this website are all about? Take a look at our Glossary of Terms definitions below:



Analogue Line

This is what you normally have at home: A single telephone line used mainly for voice.


Asymmetric Digital Subscriber Line (ADSL)

This is the technology that enables businesses to receive broadband using extensive telephone networks. Essentially ADSL makes the line faster.



An automated voicemail feature that transfers callers to extensions or departments by selecting options via dialling digits. For example, ‘press 1 for Customer Service, 2 for Returns’ and so on.


Automatic Call Distribution (ACD)

An Automatic Call Distributor/ Distribution System is a device/system that intelligently routes incoming calls to the appropriate person based on certain factors. This is particularly suited to large companies with high volumes of inbound calls where a customer can speak to a number of people about a specific query.



Bandwidth is defined as the amount of data which can be transferred over a connection, and is measured in bit/bytes per second.


BRI- Basic Rate Interface

Also often referred to as ISDN2. BRI is a service level that provides a channel for data or speech and a channel for signalling information. A BRI circuit can carry two independent calls at the same time. It is suitable for smaller businesses, larger enterprises might use a PRI (Primary Rate Interface), which carries more.


Bring Your Own Device (BYOD)

BYOD or “Bring your own Device” refers to the growing trend of employees bringing their own devices into the office to use for work purposes. It offers flexibility and remote working, therefore increasing productivity.


Byte, Kilobyte (KB) & Megabyte (MB)

How data is measured. One Kilobyte (1KB) equals 1024 bytes. One Megabyte (1MB) equals 1024 Kilobytes (KB).


Call Barring

Stops calls to certain destinations or premium rate numbers. Call barring can be applied to a whole telephone system or on a user level, affecting specific lines only.


Call Forwarding

Also often referred to as call diversion. Extension users can redirect calls to a different destination by dialling a code. The call could be forwarded to another extension, the operator, or an external number. There are different types of call forwarding, e.g. Diversion of All calls, Diversion if Busy, Diversion if no reply, etc.


Call Logging

Information collected about in or outgoing calls made on a telephone system. This data is often used for reporting and management.


Call Management

Involves a specialist software that analyses telephone system call records. This is often used to identify misuse, allocate calling costs to departments and verify if resources are adequately allocated.



A telephone service provider, for example, BT, Cable and Wireless, NTL etc. Carriers typically own their own infrastructure or Network.


CCU – Central Control Unit

Where the equipment that controls the telephone system is housed, usually a box or a cabinet.


CDR – Call Detail Record

Documents call details, CLI (Caller Line Identity), Date, Time, Number Dialled, Destination, Duration and cost. A CDR is often used for bill generation and analysis.


CLI – Calling Line Identity

Commonly known as a Telephone number. Several CLIs can be associated to one line, and several lines can be associated to one number.



When two telephone users or more join a single call. More sophisticated conference calls for larger groups of people can involve specialist software and dial-in codes.


Contact Centre

A more sophisticated version of a call centre, using unified communications (i.e. telephony, email, messaging) in conjunction with CRM applications.



Allows for both voice and data to run over the same connection.


CRM – Customer Relationship Management

A database that contains customer records and information relating to their accounts, e.g. contact details, current and past orders, payments made etc. Examples are: Salesforce, Oracle


Digital Subscriber Line (DSL)

DSL stands for “Digital Subscriber Line” and is the technology which enables the transfer of data over a phone line without interference.


DDI – Direct Dial Inward

Also often referred to as an extension. This number assigned to a specific handset and will be associated to the main number (CLI), i.e. a company’s general contact number.



Ethernet in the First Mile (EFM)

Ethernet in the First Mile (EFM) is a cost-effective alternative to a leased line; it uses fixed-band connectivity to provide a high-speed service capable of exchanging large volumes of data.



The Exchange relates to a telephone Exchange located in a central office that services a certain geographical area and denotes the service area that your connection is associated with. It is essential that the exchange has the capability to provide you with your required data line. i.e. an EFM or leased line.



Fibre to the Cabinet (FTTC)

“Fibre to the Cabinet” or “FTTC” offers high bandwidth at an affordable price. From an end-user perspective, FTTC works in much the same way as ADSL-based broadband, except that it is much faster.


Fixed Line

The term fixed line usually refers to a solution or product that uses the public telephone network such as a telephone line.


Fibre to the Premised (FTTP)

A broadband solution that delivers fibre-optic communication all the way to the premises of the subscriber, thus being even faster than FTTC.


Follow the Sun

This is a reference to a type of workflow in which tasks are communicated daily between work sites located globally, that are many time zones apart. The idea is to minimise project delivery timelines and improve response times.


Generic Ethernet Access (GEA)

Using existing Broadband and Ethernet networks, GEA is delivered over the copper wires connecting your building with the cabinet in the street. The connection to the exchange is then carried by fibre. The last part of the connection is carried by Ethernet.


High Definition Video Conferencing

High Definition Video Conferencing enables real-time, face to face conferencing either through an existing compatible telephone system infrastructure or via an external HD Video Conferencing system. High Definition offers users a much better experience, with enhanced sound and visuals, and is perfect for encouraging collaboration across geographical areas and reducing the costs traditionally associated with organising meetings and conferences.


Hosted Telephony

A cloud service solution where your phone system is hosted elsewhere in a data centre in the cloud.
A hosted telephone system will be delivered through user licenses paid by subscription. The handsets will be kept in the customer premises, but the equipment running the system will be hosted in the data centre.


Hunt Groups

A system of finding a free extension to answer a call. There are different types available, First Free or Terminal Hunting will search for the first free extension in the group, so one person gets most of the calls. Circular or UCD (Uniform Call Distribution) Hunting will share calls equally amongst the group.



Internet Protocol (IP)

The process of routing information from one network to another.


Internet Service Provider (ISP)

ISP stands for “Internet Service Provider” and is defined as the company that supplies your connection.


IP Address

A unique number that identifies the equipment sending or receiving data.


ISDN – Integrated Services Digital Network

The simultaneous digital transmission of voice, video, data, and other network services over the public telephone network. There are two types of ISDN lines:
ISDN2 –offering 2 voice channels, if more are required, several ISDN2 bearers can be presented over one number
ISDN30 – Ultimately a 2mb circuit divided into 30 channels. At least 8 channels must be open, you can then increase the capacity 2 channels at a time without installing any more bearers until you reach 30.
BT will switch off the ISDN network by 2025. SIP trunking is a viable alternative to this service.


ITSP – Internet Telephone Service Provider

Service Providers offering digital telecommunications services based on Voice over Internet Protocol (VoIP).



LAN – Local Area Network

Allows PCs to communicate with each other and common devices, such as printers or servers also connected to the network.


Leased Line

A Leased line is the most reliable type of internet connection and is often referred to as a premium line. It is usually delivered via fibre-optic technology. Using a leased line guarantees that your business will be the only one using that line (also known as one-to-one contention), thus providing a guaranteed high level of service. High-speed connections of up to 1Gbps are available via lease lines.


A popular free and open-source computer operating system (OS).

Linux Server

A variant of the Linux open-source operating system,  designed to deal with the more demanding requirements of business applications, e.g. network and system administration, database management and web services.


Multiprotocol label switching (MPLS)

Multiprotocol Label Switching (MPLS) is a means of directing data which involves assigning packets of data distinct labels. How data is distributed is then dependent on these labels.



Network Switch

Allows multiple devices to access the same network.


NGN – Non Geographic Number

Usually 0300, 0500, 0800, 0808, 0844, 0845, 0870, and 0871 numbers that are not geographically bound. This also includes premium rate numbers that are priced a lot higher. These numbers are inbound only and cloud-based.



PAC or PAC Code – Porting Authorisation Code

A code that allows you to change mobile phone network providers and transfer a phone number from one phone to another.


PBX – Private Branch Exchange / Private Automated Branch Exchange

A telephone switching system that connects telephone extensions with each other, as well as to the outside telephone network.


Point- to- Point (P2P)

This is a type of communications connection which is a dedicated data link between two designated sites, systems or processes.


Port or Number Porting

Porting means changing Network providers without changing your number. It is typically seen for Mobile, O2 to Vodafone or in fixed line, BT to another carrier. Porting numbers can be a lengthy process, which is why it is sometimes easier to get a consultant company to help.


POE – Power over Ethernet Switch

A device that passes electrical power along with data on Ethernet cabling.


PSTN – Public Switched Telephone Network

Also known as the traditional telephone network.



QoS – Quality of Service

The level of service defined by an agreement between a network provider and user that guarantees a certain level of bandwidth and data speed.



SDSL – Symmetric Digital Subscriber Line

Like ADSL, but allowing the same upload and download speed. It enables more data to be sent over existing copper telephone lines at rates of up to 3Mbps


Session Initiation Protocol (SIP)

A form of VoIP used for controlling communications that are of a multimedia nature, such as voice or video calling via an IP network. Video Conferencing, File Transfer and Messaging can all be facilitated via SIP. SIP is also a good alternative to ISDN.


SLA – Service Level Agreement

Guarantees a measurable level of service between receiver and provider.



This is the term used for a device that connects local area networks.



TCP / IP – Transmission Control Protocol / Internet Protocol

The way data is transferred only, in very simple terms, how it is packaged, sent and unpacked again on the other end.



A telephone exchange line that receives and makes calls.



Unified Messaging

A platform for the management of voice, fax and email from a single user interface.


Unified Communications (UC)

Unified Communications (UC) is a business communications strategy that looks to combine various different strands of communication types, such as telephony, presence technology, instant messaging (IM, for example Facebook Messenger), email, voice mail, video conferencing and more into a single, integrated interface. Any UC strategy will be specifically designed with a company’s unique needs in mind, including the working habits and requirements of its employees.


Unified Presence

This is the idea that a User’s availability can be seen at any time using Presence Technology, an application which can identify a device wherever it is whenever the user connects to the main network.




Usually acts as a “centralised answering machine” for users of a telephone system. Callers will listen to a personalised message and have the option to leave a message for the person they tried to reach. Many voicemail systems will also offer a routing system that directs callers to the relevant departments and give information out to callers.


Voice over Internet Protocol (VoIP)

“VoIP” or “Voice over Internet Protocol” is the digital alternative to using conventional landlines for communication and collaboration. The low cost of VoIP is its biggest draw for many businesses.


VPN – Virtual Private Network

Offers inter-site communications that can be implemented over fixed circuit connections but also via a dial-up connection, which can offer great cost benefits to the user.



WAN – Wide Area Network

Enables all users in different sites to access the same information as if they were all connected on one local area network (LAN).

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