The Telecoms Glossary

Do you know your BRI from your PRI? Any clue what the difference between an on-premise and hosted solution is? No idea what call transfer, routing or barring means?

If you’re new to telecoms, you might have seen lots of strange terms and acronyms floating around, like VoIP, SIP or ISDN. The technical terminology of the telecoms industry can be hard to get your head around. We’ve put together the ultimate telecoms glossary so you can get to grips with the industry jargon.

A – C


Stands for Asymmetrical Digital Subscriber Line. ADSL is a type of broadband connection used to connect to the internet. It transforms existing copper wire connections between the telephone exchange and telephone socket into a digital line that allows broadband access.


Amplitude is a type of energy wave. A high energy wave has a high amplitude and a low energy wave has a low amplitude.


Analogue is a type of electrical signal that transmits information. With analogue technology, the information is translated into electric pulses of varying amplitude.


Stands for Analog Telephone Adaptor. ATA is a type of hardware that converts audio, video and data signals into IP packets that are sent over the internet. ATA connects standard phone lines to high bandwidth lines to make VoIP calls.


Audio is a sound that’s recorded, reproduced or transmitted. An audio signal is a representation of sound that uses an electrical voltage for analogue signals or a series of binary numbers for digital signals.


Authentication is a security measure or process that verifies the identity of the user or subscriber. Its framework controls access to computers, enforces policies and audits usage. This authentication is usually based on a username, PIN or password.

Auto attendant

An auto attendant is an automated system that answers and routes incoming calls to the right place within an organisation.


Stands for Amazon Web Services. AWS provides on-demand cloud computing platforms to companies.


B-ISDN or Broadband ISDN is an ISDN standard that transmits voice and video data over fibre optic telephone lines.


Bandwidth is the maximum rate of data transferred during a given time period. A high bandwidth means data is transferred at a fast pace. A low bandwidth means data is transferred at a low pace.

Bearer channel

A B-channel or a Bearer channel is a user channel on an ISDN circuit. It’s used to carry voice and user data.


Stands for Busy Lamp Field. BLF is a visual indication of status for lines or extensions through LED lights.


Stands for bits per second. A bps is a common measurement of data speed for computer modems and transmission carriers.


Stands for Basic Rate Interface. BRI is an ISDN configuration, primarily used for voice-grade telephone services.


Broadband is a wide bandwidth data transmission which transports signals and traffic. It’s a high-speed internet connection and can be delivered via cable, optical fibre, radio or twister pair lines.


A browser is software used to access the internet. Many systems like 3CX use browser-based extensions so users can access their system via desktop or mobile.


A cable is an assembly of wires used to carry an electrical current.

Call barring

Call barring is an action that prevents calls from reaching their destination. Call barring lets you stop certain types of calls being made from your phone or being received by your phone.

Call divert

Call diverting is the action of diverting or sending calls to other phones. A call can be diverted to mobiles or desk phones. Also known as call forwarding.

Call forwarding

Call forwarding is a feature that helps divert or send an incoming phone call to another destination. This can be another extension, operator or external number. Also known as a call divert.

Call logging

Call logging is the collection, evaluation and reporting of data about phone calls.

Call menu

Also known as IVRs or auto attendants. When people call into a business, they’ll be sent to a call menu. This allows callers to choose a department or team member that they wish to talk to by selecting a menu option. A call menu helps direct callers more efficiently and saves time.

Call pattern

A call pattern or call pattern analysis is a technique used to identify patterns in call traffic. This technique identifies and understands callers’ behaviour and monitors and prevents any breaches of a phone system.

Call queues

A call queue places incoming calls into a line to be answered when a team or individual isn’t immediately available to take the call. When someone is available, they’re put through. A call queue is typically accompanied by music or pre-recorded messages.

Call recording

Call recording is a feature that records a phone call so it can be saved and listened to in the future. This is a helpful feature for sales and support teams for training purposes.

Call traffic

Call traffic is the transmission of phone calls over a network. It can be used to identify patterns such as when calls are made, the length of calls and minutes of use.

Call transfer

Call transfer allows you to relocate a telephone call to another person or location using a corresponding phone extension or number.


A carrier is a telephone service provider.


Stands for Call Flow Designer. A Call Flow Designer is a 3CX feature that allows you to handle how incoming calls are handled and create complex calls flows without programming or scripting. The CFD means you can route calls based on the day, direct calls based on customer input, implement a voice payment gateway and more.


A channel is a communications path between two systems that transmit and receive information and data.


Online chat is a type of communication over the internet that sends and receives real-time messages. A few examples of online chat or instant messaging are Facebook Messenger, WhatsApp and Microsoft Teams.


A circuit is a physical path that electrical signals pass through.

Circular call

A circular call is a way for calls to be routed or transferred within a hunt group. The way it works is the first call rings one phone first and the next call rings the second phone in the group first and so on throughout each of the lines. This continues until the call reaches the end of the hunt group extensions. This then starts over at the first line until someone answers the call.


The cloud is the internet. Specifically, the cloud is everything you can access remotely over the internet. If something is in the cloud, it means it’s stored on internet servers – like hardware and software services for example.


A codec is a device or program that converts data packets of a segment of hardware or software so it can be delivered, received, used, stored and encrypted. This is done by compressing or decompressing and encoding or decoding data packets.


Collaboration is the process of two or more people or organisations working together to complete a task. Within telecoms, collaboration platforms create a unified workspace that includes data, voice, video, files and IP communications into a single system.


Concurrent calls indicate the number of simultaneous calls that a line or SIP channel can handle.

Conference bridge

A conference bridge allows a group to participate in a phone call. It’s a device for PBX systems that sum and balance energy levels between calling parties.


Conferencing is the joining together of more than two telephone users in a single call. This can be audio or video conferencing.


Configuration refers to the way components are arranged to make up a phone or computer system. It consists of both hardware and software components.


Connectivity describes how well hardware or software devices communicate with other devices. It’s the capability for the interconnection of platforms, systems and applications.


In relation to leased lines. A contended line is a line or bandwidth that is shared amongst users of a local area. The opposite of a contended line is an uncontended line.

Copper wire

A copper wire or line is a traditional physical telephone line used to transmit analogue voice communications.


An electrical current is a stream of charge particles that move through an electrical conductor or space.

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D – F

Data packet

A data packet is a basic unit of communication over a digital network. When data is transmitted, it’s broken down into similar structures of data which are then reassembled to its original state once they reach their destination.

Delta channel

A Delta channel or D-channel is a user channel on an ISDN circuit. It’s a combination of data, packet networking, control and signalling.


Stands for Digital Enhanced Cordless Telephony. DECT is a technology that providers clarity and handsets for cordless phones.


Digital is a type of electric signal that transmits information. With digital technology, the information is translated into a binary format where each bit is representative of two distinct amplitudes.

Direct Routing

Direct Routing is the process of routing Microsoft Teams to the PSTN, converting it into a fully-fledged business phone system.


Stands for Demilitarized Zone. A DMZ is a physical or logical subnetwork that contains and exposes an organisation’s external-facing services to an untrusted network. Its purpose is to add an additional layer of security to a business’ local area network.


Stands for Domain Name Service. DNS translates IP addresses into domain names.


Stands for Data Over Voice. DOV is a technology used for transmitting data and voice simultaneously over twisted-pair copper wires or an ISDN line.


Stands for Digital Service Zero. It’s a 64 kbps/s pipe used for data and signalling.


Stands for Digital Subscriber Line. A DSL is a family of technologies that are used to transmit digital data over telephone lines. It’s typically referred to as an ISDN line.


Stands for Ethernet over the First Mile. It’s a type of leased line connection that uses the traditional copper network to deliver a connection, then a full fibre ethernet connection from the exchange. It uses aggregated copper pairs and offers speeds up to 35 Mbps.


An endpoint refers to any device that is a physical endpoint to a network. Examples of endpoints are servers, desktops, laptops and mobile phones.


Stands for Ethernet over FTTC. EoFTTC is a type of leased line connection. It uses a mixture of fibre and copper lines and is a cost-effective dedicated connection that uses existing cabling and infrastructures. They offer speeds up to 76 Mbps.


Ethernet is a system that connects customer systems to form a local area network. It’s a family of computer networking technologies. Fibre Ethernet is a direct, superfast ethernet connection using over100% fibre optic cables from the business premises to the ISP. They offer speeds up to 10 Mbps.


An extension is an additional telephone line wired to the same telephone line as another.

External calling

An external call is a call that is made to or received from external numbers on the PSTN. If a customer or someone from outside your business calls into your organisation, that’s an external call.


Fibre communication is a method of transmitting information from one place to another by pulses of light (waves) through an optical fibre line.


A firewall is a post of a phone/computer system or network that’s designed to block and filter unauthorised access from outside a local area network. It also allows authorised communications in and out of a company’s infrastructure. It’s a security tool that can be implemented using hardware, software or both.


Stands for Fibre to the Cabinet. FTTC provides a super-fast broadband connection over fibre optic cable from the telephone exchange to local street-side boxes.

G – K


A gatekeeper is a person who controls access to something, like the internal communications of a business.


A gateway is a router in a computer network that communicates and sends data back and forth and blocks harmful things from infiltrating a network. It’s a key stopping point for data on its way to or from other networks.

Gigabit (gbps)

Stands for gigabits per second. A gigabit is a measure of data transfer rate equal to 1,000 megabits per second.


A handset is the physical part of the phone that you can hold and use.


Hardware is the physical equipment of a phone or computer system, like monitors, wiring, desk phones, keyboards, tablets and speakers.


A hosted solution or hosted PBX is a service that’s delivered by a service provider in their own private data centres. This provider provides the physical servers to run your phone network.

Hunt group

A hunt group distributes calls from a single phone number to a group of numbers in a company. When callers ring your company phone number, the hunt group routes the call to a group of members so they can answer it. It’s a popular feature of a phone system.


Stands for Inter-Asterisk Exchange. IAX is a protocol used by Asterisk phone systems to connect multiple Asterisk servers and devices.


Infrastructure is the set of fundamental facilities and systems that support the functionality of a business and its systems.


An interface specifies signalling and management functions between two networks.

Internal calling

An internal call is a call made to or received from internal numbers on the PSTN. If a colleague or someone from inside your business calls you or your organisation, that’s and internal call.


The internet is a global network of computers that enables computers to send one another digital data packets.


Stands for Internet Protocol. IP is a communications system that routes data from one computer to another over the internet, using a set of formats or rules.

IP address

An IP address is a fixed or dynamic number that’s associated with an internet-enabled device.


An IP PBX is a PBX system with IP connectivity. It connects telephone extensions to the public switched network and provides internal communications for a business.


Stands for Integrated Services Digital Network. ISDN is a set of communication standards that used digital transmission to make audio and video calls, transmit data and other network services over the circuits of the PSTN. The ISDN is being switched off in 2025.


Stands for Internet Service Provider. An ISP is a company that provides you with access to the internet.


Stands for Interactive Voice Response. An IVR is an automated telephony system that interacts with callers, routes calls and gathers information to be sent to the right person or team. Also known as a virtual receptionist.


Stands for kilo bit per second. A k/bit is a unit of data transfer rate.

L – O


Stands for Local Area Network. LAN connects computers to each other within a group or area.


A landline phone uses physical metal wires or optical fibre lines to enable and transmit phone calls.

Leased line

A leased line is a dedicated, fixed-bandwidth data connection. It provides businesses with a reliable, high-quality internet connection with guarantees of upload and download speed, uptime and resilience.


In relation to 3CX and Microsoft Teams. A license is an official permit to use or own something. Depending on certain systems, you may or may not need a license to use them.


A line is an electrical connection between a telephone service provider’s switch and a telephone terminal or key system. Lines can be virtual or physical.

Megabits (mbps)

Stands for megabits per second. Mbps is a unit of measurement for broadband and represents a million tiny units of data.

Microsoft Teams

Microsoft Teams is a business communication and collaboration platform created by Microsoft. It offers chat, collaboration, calling and file sharing all in one place for businesses to work with and stay connected to their colleagues.


Migration is the movement from one part of something to another. In telecoms, this can be moving communications or phone numbers from one system to another.


A mobile phone is a portable handheld device that makes and receives phone calls.


An abbreviation of modulator-demodulator. A modem is a hardware device that converts data into formats suitable for transmission mediums so it can be transmitted from computer to computer.


Stands for Narrowband ISDN. N-ISDN is a type of ISDN standard.


A network is the equipment and transmission facilities for communication between computer or phone systems.


Stands for Network Management Service. NMS is a computer system that’s used to configure and manage a telecoms network.


An on-premise solution is a system that requires a business to install and look after their physical hardware in their office. This is the opposite to a hosted solution.

P – S


A packet is a collection of data used by computers to communicate with each other. The data is in the form of computer signals which are encapsulated and sent across the network.


Stands for Portable Batch System. A PBS is a type of software used for job scheduling.


Stands for Private Branch Exchange. A PBX is a private telephone network used within a company or organisation. A PBX can be a hosted or on-premise solution.


A platform is a set of software and a surrounding ecosystem of resources that helps grow a business. A computing, digital or software platform is the environment in which a piece of software is executed. This could be hardware, an operating system or a web browser.


A plug-in is a software component that adds specific features to an existing computer platform or program.

Point to point

Point to point is a type of connection that refers to a communications connection between two endpoints.


Porting or number porting is the process of moving an existing phone number from one communications provider and transferring it to another.

Premium rate

A premium rate telephone number is a number for calls during which certain services are provided and prices are charged at higher than a normal phone call. This call charge is paid to a service provider.


Stands for Primary Rate Interface. PRI is used for carrying multiple Digital Signal 0 services and data between the ISDN network and a user.


Provisioning is a configuration of an IP phone through the IP telephony server or PBX.


A protocol is a convention or procedure between two points during data communication.


A provider or service provider is a company that provides organisations with communications.


Stands for Public Switched Telephone Network. It’s the system that’s been in use since the 1800s and is the world’s combined circuit telephone network. It has developed from being an analogue system to completely digital.


A router is a networking device that routes and forwards data traffic and packets between computer networks. Routers are used to connect LANs together or LANs and ISPs.


Stands for Software as a Service. SaaS is a software licensing and delivery model in which software is licensed on a subscription basis and is centrally hosted.


A server is a piece of computer hardware or software that provides functionality for other programs or devices. A server can be local or remote.

Session Border Controller

A Session Border Controller or SBC is a device that’s deployed in SIP-based VoIP networks to protect and regulate communication sessions.


A signal is an electrical impulse or radio wave that carries information.

Simultaneous call

A simultaneous call is a way for calls to be routed or forwarded in a hunt group. When a call comes in, all the phones in the group will ring at the same time. The members or operators in the group can pick up the call if they are available to.


Stands for Session Initiation Protocol. It’s a communications protocol used to make, set up and manage sessions with users over the internet. SIP is used in the initiation and termination of VoIP calls.

SIP channel

A SIP channel is the capability to support incoming and outgoing calls. Every SIP trunk contains a number of channels, which are virtual versions of telephone lines. The number of channels you need depends on how many concurrent calls your business makes.

SIP Trunk

SIP Trunks enable the PBX’s end point to send and receive calls via the internet. As SIP controls and manages the sessions, SIP Trunks control voice, messaging and video applications.


A softphone is a type of software for desktops, tablets and laptops that provide VoIP call services. Rather than being a physical phone, it’s on a computer. A softphone receives input from a microphone and outputs through speakers or headphones.


Software is a collection of data or instructions that tells a computer or a phone how to work.


In relation to leased lines. A leased line must be symmetrical, meaning they have the same upload and download speed.

T – W


Telecommunication is the transmission of information by various types of technologies over wire, radio, optical or other electromagnetic systems.


Telephony is a field of technology that involves the development, application and deployment of telecommunication services.


Transmission is the process of sending and propagating an analogue or digital information signal over a physical point-to-point medium.


A trunk is a telephone exchange line that makes and receives calls. A trunk used to refer to a bundle of phone lines shared between users. Modern trunking refers to a virtual link between your PBX and the PSTN using an internet connection.


Stands for Unified Communications as a Service. UCaaS is a cloud-delivered unified communications model for enterprises and businesses.


In relation to leased lines. An uncontended line is a line or bandwidth that isn’t shared with other users but is solely dedicated or owned by a business or organisation. The opposite of an uncontended line is a contended line.

Unified Communications

Unified communications is the integration of enterprise communication services, including instant messaging, voice, mobility, audio, video conferencing, data and desktop sharing, all in one place.

Uniform call

A uniform call is a way for calls to be routed or forwarded in a hunt group. This is when a call is sent to the phone which has been idle or unused for the longest. If this line is busy, the call will go to the next idle line and so on.


Uptime is a measure of uninterrupted time that a hosting system experiences. It’s expressed as the percentage of time that a system has been working or available. Ideally, uptime should be at 100%.

Video conferencing

Video conferencing is technology that allows users in different locations to hold face-to-face meetings.


Voicemail is a central answering machine for phone system users. The user diverts calls to the voicemail system if they’re unable to answer the call. A personalised message will play for the caller who can then leave a message for the user.


Stands for Voice over Internet Protocol. VoIP is the basis for most modern phone systems and uses the internet to make and manage phone calls.


Stands for Wide Area Network. WAN is a network that extends over a large geographical area for the purpose of computer networking.

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