PBX & IP Phone System Terms & Definitions

(Yah, a boring read. But, worthy of your time!
We did use spell checker, crust me on this.
Grammar may be off muchly though.)

Telephone Glossary - Understanding Telecom Terminology


Stands for Private Branch Exchange, which is a 'private telephone network' used within a company or organization.

Analog Lines - POTS Lines, PSTN Lines, Landlines

Analog lines are older copper wire / telephone line service standards. Also known as: POTS = Plain Old Telephone Service and PSTN = Public Switched Telephone Network, landlines or the traditional circuit-switched telephone network service.

VoIP = Voice-over-IP

Voice-over-IP is now the commonly accepted method of providing telephone & voice communication service over data network, or internet. 

Sometimes confused with "IP" phone or telephony, the technology is analogues but services differ depending on the type of service required. VoIP now tends to encompass several services including external / internal communication service, telecommunication and telephone line service through the digital data. Voice & video have now become covered when referring to "related VoIP services".


Is a "broad term" used for IP & VoIP telephone and telecommunications infrastructure. It can include both hardware and software based services and is a simply a 'general term' used for a host of services and telephone features.

Ring Group

Ringing two or more extensions in a "group" or ring multiple extension sets as a group. Examples of use are for when a caller calls in, and dials a code or chooses an IVR menu selection item - then is routed to reach different groups of extensions the company desires. IE: "Reception Group", "Sales Group", "Support / Customer Service Group", etc.

IVR - Interactive Voice Response

Interactive Voice Response (IVR) is a technology that allows humans to interact with a computer-operated phone system through the use of voice and DTMF (touch tone) selection over telephone lines. IVR is also known sometimes as an "Auto-Admin" menu system.

Usually a pre-recorded voice message which described key selections available to choose from (usually 0-9 and * or # and direct dial to extension numbers from the menu). The caller is then directed to various options available as described from the recorded voice greeting.

Hunt Group

Hunt group is older PBX system terminology. Now properly described as "Outbound Route" and/or "Inbound Route" depending on the PBX manufacturer's use of the term. Usually an 'outbound calling function' that selects a telephone line, or group of lines to route an outbound caller through. Hunt Group is also sometimes defined as an inbound "Hunt Group" (which in today's terms should be referred to as 'Inbound Route' instead). 

If you ever use a Dial 9 for outbound lines from a business phone system, that is what was used for selecting an outbound Hunt Line or from a Group of lines. Just like adding a 5, 6, 7 or 8 to a phone number to dial out through different lines - these types of functions can still be used for different purposes in today's business. Example - if you have multiple companies on the same phone system, Dial 9 can allow the outbound caller to call out and use caller ID for Company A. Dial 8 can allow the caller to call out on designated lines and use the caller ID for Company B, and so on.

Extension Group

Similar to "Ring Group". But, in our PBX Phone Systems extensions can be "Grouped" as linked extension sets in a defined group set to more easily configure certain features. 

IE: Extensions 101, 102, 103 can be set-up as a "Sales Extension Group", just as multiple other extensions can be set-up in differently named groups to streamline system set-up features. Callers can reach either one "Ring Group" when dialing a code, or multiple groups of ring groups. So say you want callers to press 1 during the IVR to ring Sales Group. But, when they press 2 for Customer Service - both Sales Grouped and Customer Service Grouped extensions ring as one ring group even though they are separate ring groups. Essentially Groups of Groups can be paired and ring together under desired circumstances.

Inbound Route / Outbound Route = Call Routing

As described above, this is how you set-up or manage inbound and outbound calls. A route is simply how you designate the call handling features under preset calling designations rules.

Call Transfer

When a caller is handled either automatically through the IVR or by a party inside the PBX, call transfer allows the caller to be transferred between extensions or other features on the phone system. Call transfer can happen either automatically in the system under preset conditions, or manually by the users when in active calls.

Call Queue - Call Center Functions

Call Queue is simply a method of holding a caller in queue, until one or more agents / extension users are available to take their call directly.

Other features that fall under this system functionality are "Music on Hold", On-hold advertising sound files, etc. Call Center functions generally also have fail-over options that allow callers to be manually or automatically transferred to other parts of the company PBX in certain situation. Call Center functions may also include Call Monitoring / Recording / Barge and Whisper (Administrator) to Agent features for managing employee and customer service agent interaction with callers.

Call Back

Usually falls under Call Centre functions, the caller can hang up and request and automatic call back if they do not wish to remain on hold. Some call center functions allow the user to input their number or another number for the call back to take place when an agent is available to take their call.

Sometimes this feature can also be used to filter spam calling by having an announcement for inbound callers to enter their number to receive a call back, instead of someone actively taking the call, or forwarding the caller to voicemail.

Call Hold

As simply put - holding a caller until extension or user can resume an active call with them. Hold usually is handled at the user extension level only or when a caller is forwarded to a call queue to hold until agents can accept their call.

Call Park / Orbit

Call Park (also referred to as "Call Orbit") is a "global" hold function. Callers can be parked in a globally accessible queue where they can be picked up from any other extension on the system by pressing a pre-programmed button or dialing a call park orbit code.

BLF - Busy Lamp Field

BLF is an acronym for 'Busy Lamp Field', which is a light on an IP Phone or a colored indicator next to a name in a soft phone or web client. It is a visual indicator that shows whether another extension connected to the same PBX is available, busy or in use. Also sometimes referred to as "BLF Presence" monitoring.

Overhead Paging / Group paging

Overhead paging is a function that allow a user to announce information, through IP phone speakers, overhead wired speakers, outdoor speakers and / or other internal building speakers (if installed). Paging can be done to 'all speakers at once', or just IP phones, or outdoor/overhead speakers when set-up as groups. Sub-paging 'groups' also allows only specific users or groups of users to receive an overhead paging announcement if set-up as such. IE: Sales group paging, Support Group Paging, Page-All, etc. just as described in "Ring Groups & Extension Groups".

Call bridge / DISA features

Call Bridge and "Direct inward system access (DISA)" service is a useful IP-PBX system service for enterprise communication markets. DISA permits outside users to call in on telephone serice lines, then log into the PBX and to use internal system features. Once they pass authorization, they can use the restricted internal PBX features to action different things, such as: call back out through a company line, access a group page function, and more.

Pick-up Groups

Offers the ability to pull a ringing call to the phone you are currently on. Group call pickup, this allows you to collect a call from any ringing phone that is in the same pickup group as you, if there were more than one phone ringing then you would have no control over which call you collected.


This feature allows users to use one phone, but multiple users can login to that device and use their own preset configuration and features tied to their own desk phone configuration.

Group voicemail

Like regular voicemail - except this feature generally 'copies' the same voicemail message to all users voice mail boxes at once, who are in the voicemail group.

Announcement Center

Allows the PBX System Administrator or Users to provide pre-recorded 'audio annoucements' or sound files that callers and users will listen to. Announcement centers can also fail-over or forward to other features once the pre-recorded announcement has ended playback.

Follow-me (Call Forwarding Functions)

Call handling features which allow callers to be auto-forwarded to other extension or external numbers if a user's extension is not answered after X number of rings. Can also be used for time-scheduling features to function on specific days, times or periods the user designates.

DID - Direct Inward Dialing

Direct Inward Dialing (DID) is a service of a local phone company (or local exchange carrier) that provides a single number or a block of telephone numbers for calling into a company's private branch exchange (PBX) system. Using DID, a company can offer its customers individual phone numbers for each person or workstation within the company without requiring a physical line into the PBX for each possible connection.


WebRTC = Web Real-Time Communication. It offers multiple communication channels and other system integration possibilities, such as: video conferencing, data sharing, instant messaging, etc. In addition, it is accessible from anywhere, as long as you have an Internet-connected device at hand. WebRTC technology also allows companies to integrate their communication with other applications, for example, with various CRM systems.


Asterisk is recognized as the standard software implementation side of a private branch exchange (PBX). Commercial private and proprietary systems all usually have some form of Asterisk implementation involved so they can communicate with other end-points and services in the Telecommunications industry.

T.38 / Fax Protocol

Fax protocol T.38 is a specialized fax transmission protocol that allows faxing over VoIP Telephone Line and other network / IP services.