Jargon associated with Telephony and AASTRA - MITEL Telephone Systems

The alphabetically listed information below is provided by way of a guide to understanding some of the vocabulary and abbreviations used on this website. Terminology used by other manufacturers and service providers may differ from those we have used.


ABB Dials ‘Abbreviated Dialling’ is a term used to store names and telephone numbers in a phone system that can be accessed by all staff either by short code (7001 for AASTRA) or Predictive Dialling.

AIN ‘AASTRA Integrated Network’ is an AASTRA term used to describe the integration of a number of remote AASTRA sites into one large system. The system is managed as a master (head office) with a number of Satellites. Connectivity for voice and data can either be completely VoIP (when leased lines are used) or a mix of SIP and ISDN (when ADSL Broadband is used)

Alpha Tagging is a standard feature on AASTRA systems that enables the inbound caller’s name to be displayed on an AASTRA handset should their number be stored in the system as either an ABB Dial or PISN number.  This feature is, however, dependent on the caller forwarding their CLI.

ACD ‘Automatic Call Distribution’ is a system with associated software allowing for the automatic queuing and distribution of inbound calls.  Call stats (live or historic) are available with associated software, live call reporting can be viewed on large flat screens.

AD2 / DSI is a term used to describe a ‘proprietary connection port’ for AASTRA Desk-phones. One port can provide two separate digital connections which provides for two completely independent subscribers... but only when located close together e.g. in the same office.

AMC is an AASTRA application delivered Over the Air (OTA) to compatible GSM Mobile phones providing Fixed Mobile Convergence FMC with either AASTRA IntelliGate or 400 system platforms.

AMC + (iPhone) is an enhanced solution that offers the same features as AMC but includes an additional hardware controller allowing for seamless handover from GSM Network and Office PBX (via WiFi SIP connectivity) and vice versa. AASTRA 400 system platform only.

Analogue Line isa standard telephone line, as used by most people at home.  It is required in most cases for the delivery of an ADSL broadband connection.

Analogue (ab) Extension is used to connected standard telephones POTs and other analogue devices e.g. fax, franking and credit card machines to digital telephone systems etc.

Auto Attendant is an automated answering system that allows the inbound caller to select the destination of their call e.g. ‘Press 1 for Sales’, ‘Press 2 for Accounts’ etc.  It can also be used to give the caller access to standard information e.g. swimming pool time tables at a leisure centre etc.

AUX Working (aka Auxiliary Group)is used to describe a number of analogue PSTN lines grouped together under one number e.g. a business may have one telephone number provided across three lines, should one line be busy then calls will ring in on another.


Baluns / Modtaps are adaptors used to converted analogue telephony devices (e.g. standard telephone, fax or card machine) with a standard white BT plug to a RJ45 connection, for use with Structured Cabling

BRA see BRI below

BRI ‘Basic Rate Interface’ allows for the single connection of one ISDN 2e line providing 2 separate speech channels (lines) e.g. two BRI interfaces will permit the connection of 2 x ISDN 2e lines, providing a combined total of 4 speech channels (lines) for external telephone calls. Please refer to ISDN Circuit for more information.


Call Forwarding allows the user on an AASTRA telephone system to simply direct their calls to another destination e.g. mobile phone with the users ‘office’ CLI being shown.  This will take two ISDN channels (lines) based on the ‘inbound call’ taking one channel and then the ‘call back out’ taking another channel. Calls forwarded to a different location are chargeable as per a standard call.

Channel for the purpose of this website and telephone systems in general is a term used to describe a single ISDN route to the BT exchange. You could view this as one ISDN channel equals or replaces one PSTN analogue line

Customer Controlled Call Forwarding is an additional network (BT) service on ISDN that enables the user (on an AASTRA telephone system) to tell the BT exchange to redirect/forward the inbound calls to their number to different location e.g. mobile phone with the originators CLI should be shown.  This does not take up two ISDN channels as in the case of normal call forwarding.  Calls forwarded to a different location are chargeable as per a standard call.

CCU Central Control Unit refers to the hardware of main telephone system

CAT 5e / CAT 6 refers to a run of ‘twisted four-pair cable’ conforming to standard cabling used to carry telephony and data (Ethernet) services.  Refer to Structured Cabling.

CLI ‘Calling Line Identity’ is an additional network (BT) service on ISDN and PSTN lines that allows the inbound caller’s number to be displayed.  This information can be Alpha Tagged, allowing the AASTRA system and/or associated software to show a caller name associated to the telephone number on inbound calls.

Cloud-based Telephiones (see VOIP)

Comms Cabinet isbest described as a metal box with a clear door used to mount voice and data equipment.  Cabinets can either be wall mounted or floor standing.  The latter is normally used on larger installations.  A Comms Cabinet provides a central position for voice and data hardware e.g. ADSL broadband router, data-switch and telephone system etc.  Larger cabinets can also allow for the installation of servers.  Cables from the RJ45 sockets (refer to Structured Cabling) are normally terminated in the Comms Cabinet on a Patch Panel.

Communications Server is the new term for a modern digital IP Ready or Enabled telephone system / PBX. A Communication Server should provide all the features you would expect of a traditional PBX but with have the ability to totally integrate with IP, both for telephony and CTI applications

Cordless / walk-about see DECT below

CTI ‘Computer Telephony Integration’ is a term used to describe the linking of a telephone system and a computer network.  In its simplest form, this allows a user to seamlessly dial a contact telephone number from PC based TAPI compliant software e.g. MS Outlook.


DDI ‘Direct Dial In’ is an additional network (BT) service that allows blocks (in 10s) of consecutive numbers to be assigned to an ISDN or SIP circuit.  This then allows inbound calls to be identified by the number dialled, with the AASTRA telephone system routing calls directly to individuals or departments.  An ISDN or SIP circuit can have many more DDI numbers assigned to them than actual channels (lines).

DECT Commercial or Proprietary ‘Digital Enhanced Cordless Telephony’ is used to describe wireless handsets that communicate to their associated base stations digitally.  Proprietary base stations can support a number of proprietary DECT handsets and, where a number of base stations have been installed to cover a large area, calls will be seamlessly handed over to the base station with the strongest signal, as the user ‘roams’.

DECT Domestic (home cordless)‘Digital Enhanced Cordless Telephony’ is used to describe wireless handsets that communicate to their associated base station digitally.  This base station is then connected to one analogue PSTN line (as at home) or an analogue (ab) extension run off a telephone system.  Range and ‘roaming’ is limited when compared with an AASTRA Commercial DECT system.

DECT Headset or Cordless Headset enables connectivity without wires from the Desk-phone. Office 5370 and 5380 Desk-phones have inbuilt electronic switch hooks allowing an integrated connection with compatible headsets, therefore  no need for a stick on handset lifter

Desk-phone (as described to on this website) refers to a proprietary AASTRA telephone e.g. Office 5360, 5370 and 5380

DSI / AD2 is a term used to describe a ‘proprietary connection port’ for AASTRA Desk-phones. One port can provide two separate digital connections which provides for two completely independent subscribers... but only when located close together e.g. in the same office.


Electronic Switch Hook (Standard on AASTRA 5370 and 5380 Desk-phones) allows for an integrated cordless headset connection with compatible models, therefore no need for a stick on handset lifter.

EKM Expansion Key Module is an ad on device for Office 5370 and 5380 providing additional

ERC (External Remote Control) allows the system to be accessed via specified DDI number and 6 digit password for the administration of user features e.g. changing an out of hours 'on call' destination number over a weekend or holiday period


FMC ‘Fixed Mobile Convergence’ describes the seamless transfer from a Desk-phone to a cordless proprietary DECT handset... or (via AMC +) to a GSM mobile device.

Function Keys. AASTRA Office 5370 (12 keys), Office 5380 (non as standard). Both phones have the option to connect expansion modules - M530 (20 Keys); or M535 (45 keys) with 15 physical buttons each with 3 memory locations. Each key location is digitally labelled (no paper required). Function keys can be fully configured e.g. Team Keys, activate system feature or a Line Key for use as a Key-Telephone

Feature Key. AASTRA Office 5361 proprietary Desk-phone 10 keys that can be used as a Team Key or to activate and indicate a system feature is active, e.g. Night Service is on. Unlike Function Keys (Office 5370, M530 & M535) standard Function Keys cannot be used for Line Keys therefore an Office 5381 cannot be used as a key-Telephone.

Free Seating is a standard AASTRA 400 feature, the same as Hot Desk working described below.

FXO ‘Foreign Exchange Office’ is a term used to describe a system connection for analogue PSTN lines.

FXS ‘Foreign Exchange Station’ is a term used to describe a system connection for standard analogue telephones and devices e.g. domestic cordless phones, fax and card machines.


GSM ‘Global System for Mobile communications’ refers to the world’s most popular standard for mobile telephony systems.


Hands-free normally refers to the use of a phone without the need to lift the handset. The conversation is held via the phone’s speaker and internal microphone.  Some phones may not be completely ‘Hands-free’ but offer an On-Hook dial option instead.

Hybrid Extensions is normally a term to describe telephone system extension ports (connections)  that can be either proprietary Desk-phones or standard analogue phones

Hot Desk (aka Free Seating) working allows a telephone to have its working profile changed by the user i.e. the internal name; number and programmed features are changed via the user entering a feature code and their personal password or id.  This is ideal for shift working or shared desks.


IP PBX is a term used to describe a telephone system that can provide both traditional voice and IP connectivity i.e. Proprietary digital or IP Desk-phones; analogue or SIP Phones and DECT handsets

IP Telephony is a more standard form of signalling (from the telephone system to the handset) than that of traditional propriety signalling, where each manufacturer has their own way of communicating with their handsets. In simple terms, AASTRA IP handsets have the same features and facilities as standard digital AASTRA handsets - they just talk a different language to the phone system.  A clear advantage of IP telephony is that an AASTRA IP handset can be connected to an AASTRA IP enabled PBX from anywhere in the world, via a robust VPN data/internet connection. This makes IP handsets ideal for remote offices and remote home workers.

ISDN / ISDN 2e / ISDN 30e ‘Integrated Services Digital Networks’ are, in simple terms, digital phone lines (often referred to as channels) that provide a reliable and robust connection between a digital telephone system at the network (BT).  For more connectivity information, please refer to BRI (ISDN 2e) and PRI (ISDN 30e) descriptions.  Additional network (BT) services are available on ISDN – an improvement on normal analogue lines.  One of the most useful is DDI numbering.

ISDN circuit is a term used to describe either a number of ISDN 2e lines grouped together under one number (and associated DDI ranges if and when applicable) or one ISDN 30e connection . Example could be, three ISDN 2e lines grouped together as one circuit would provide 6 speech channels (lines). This circuit could have one or more numbers assigned to it e.g. one main number and an additional block of 10 DDI numbers, where all 11 numbers would share the 6 channels (lines) on a first used, first served basis.

IVR ‘Interactive Voice Response’ is an automated answering service that automates routine enquires or transactions either via voice recognition or telephone keypad e.g. credit card lines.


Key-phone is normally a term to describe a proprietary Desk-phone that integrates with the system via programmable buttons. These buttons normally have visual indication of use e.g. red or green


Leased Line is a (preferred for VoIP)service contract, between a provider and a customer, whereby the provider agrees to deliver a symmetric telecommunications line connecting two or more locations in exchange for a monthly rent (in effect, a lease arrangement).  It is sometimes known as a 'Private Circuit' or 'Data Line' in the UK.  Unlike traditional PSTN or ISDN lines, it does not have a telephone number, each side of the line being permanently connected to the other. Leased lines can be used for telephony, data or Internet services.


Night Service / Service Modes are terms used to describe the working mode of a telephone system i.e. in ‘day mode’ the system will route inbound calls to a sales group but at night, calls will go to a dedicated Voice Mail box.  Service modes are enabled and disabled by the user on AASTRA telephone systems by a single key press function.


OIP ‘Open Interface Platform’ - is the interface between the AASTRA PBX, the communication server and the applications (own and from third-party suppliers) and guarantees a seamless integration of CTI applications. OIP permits deep integration of the applications with telephony e.g. Subscriber Presence Indication. OIP is required for Office Suite on 400 and IntelliGate.

On-Hook Dial normally refers to a phone’s ability to monitor a call via its internal speaker, however, the user will have to use the handset for a two way conversation, since a phone unit doesn’t have an inbuilt microphone, unlike a Hands-free phone.

One Number Working allows the AASTRA system to assign one telephone number to a number of connected telephony devices i.e. one contact number for Desk Phone, DECT Handset, Soft-phone and GSM mobile... or even a loud sounding bell for workshop and warehouse environments.


Patch Panels are mounted in a Comms Cabinet and provide individually numbered RJ45 sockets, normally 24 or 48 outlets per panel.  Standard RJ45 Patch Leads then connect from the ‘patch panel’ to technical devices e.g. data switches,  telephone system or they provide through connections of standard BT lines for telephones, fax, card and franking machines etc.

PBX / PABX ‘Private (Automatic) Branch Exchange’ is an industry term used to describe a business telephone system.

POE / Power Over Ethernet to provides the ability to use low voltage power over Structured Cabling.  This eliminates the need for using a local power supply to drive devices e.g. IP telephones.

POE Switch is the same as a normal data switch, albeit some or all of the ports provide POE.

Port / Porting is a term normally used to describe a network telephone number that transfers from one Network Providers’ platform to another i.e. A BT number is to be ported onto the Talk Talk Network

POT is a telecoms term to describe a ‘Plain Ordinary Telephone’, basically a simple analogue phone as used in most homes.

PSTN ‘Public Switch Telephone Network’  is often used to describe a standard analogue line, as used by most of us on our home telephone line.

PISN in ‘Private Internal System Numbering’ that enables the AASTRA system to store external ‘in-house’ numbers separately from ABB Dials.  This allows inbound calls from these destinations to be treated as internal calls i.e. if another office number (of the same company) is stored as a PISN number, when that office calls into the system it will be treated as an internal call.  This means that an internal ring pattern and the office or person’s name can be shown.  This feature works well for multi-sites, with ISDN and DDI working, as calls can be easy transferred and identified across the various offices.

PISN out enables a name and number to be stored in the system (as described above) to be easily accessed via an ‘internal’ extension number i.e. two offices have and ISDN connection with 20 DDI numbers:  Taunton office has been assigned extension numbers 200 – 219, Bath assigned 220 – 239.  Each office can now call the other by simply dialling the extension number they require, the system automatically routes the call (via PISN) either internally (same physical office) or externally to the other.

Presence Indication can be a term used to describe a subscribers current status before and when a call is made to their extension number e.g. in a meeting, out of the office. Through AASTRA OIP Server this information can be integrated via MS Outlook™ Calendar

Predictive Dialling is a standard feature on proprietary AASTRA telephones that enables the user to easily access system ABB Dials (stored names and numbers) via entering the first few characters of the associated name required e.g. to look up and dial Avalon Telecom, the user (whilst keeping the handset down) would press 2 (A), 8 (V), 2 (A) and 5 (L) followed by the ‘phone book’ button.  The system would then look up the information entered (similar to that of predicative texting on a mobile phone) and return suggested names.  The user makes their choice and the system dials the chosen number.

PRI / PRA ‘Primary Rate Interface’ allows for the connection of an ISDN 30e circuit providing a minimum of 8 separate speech channels (lines) which can be increased in pairs to a maximum of 30 channels (lines).  It would be normal practice for ISDN 30e circuits to also have associated DDI numbers (please refer to DDI numbering and ISDN Circuit for descriptions).

QOS ‘Quality of Service’ guarantee is required to provide an acceptable and robust means of delivering voice calls via data connections.  Standard ADSL broadband circuits do not normally have a QOS guarantee, however, Leased Lines or similar services do.


RJ45 is a common standard for commercial telephony and data (LAN) connections used in Structured Cabling.


SIP Networking allows independent AASTRA systems to have linked PSIN numbering scheme for internal call handling between sites. External calls can also be transferred between sites. (Good quality dedicated data services required e.g. dedicated Broadband or Leased Line)

SIP Phones ‘Session Initiation Protocol’ Phone refers to either a Desk-phone or Cordless (SIP DECT) handset that communicates with either a PBX via IP or the Network via SIP Trunks. SIP phones can be connected to any compatible IP PBX platform and should have to access to most system features.

SIP Trunks ‘Session Initiation Protocol’ Trunks refers to digital lines provided via a data circuit, broadband or preferably through other more robust service with a QOS guarantee.  SIP trunks are not restricted by local area STD codes i.e. they can be used for businesses moving out of their local STD area to a new location and wish to keep their old number.

ST isan AASTRA term normally used to describe a single ISDN 2e interface/connection

STD ‘Subscriber Trunk Dialling’ (aka ‘local area code’) is the prefix code of your local exchange e.g. 01458 is for Glastonbury.  This is changed with emergence of SIP Trunks which are not local exchange dependent i.e. should a business move from Glastonbury (01458) to Taunton (01823), then their existing number should be able to be ported from the BT exchange at Glastonbury and provided by a SIP Trunk at Taunton.

Structured Cabling is a term used to describe a building’s CAT 5e / CAT 6 telephony and data cabling infrastructure consisting of a number of standardized smaller elements (hence structured); providing easy and reliable installation and future management of voice and data devices within a building.  Connections are made via standard RJ45 sockets (wired to 568B standard) and RJ45 (LAN) plugs for AASTRA Desk-phones and IT / Data devices e.g. PCs and printers etc.  Socket adaptors (aka Modtap/Balun) maybe required for normal telephones and other devices with white ‘BT plugs’ e.g. fax and credit machines etc.  All CAT cable runs should distribute from a central position within the building and are normally terminated in a Comms Cabinet.

Subscriber is a term used to describe a user that is ‘subscribed’ to an AASTRA system.  A ‘subscriber’ can have more than one telephony device assigned to them under the same One Number e.g. a Desk-phone and a DECT (Cordless) Handset.


TAPI ‘Telephone Application Programming Interface’ is a term used to describe a software’s compatibility to connect with telephone systems.  When used with CTI applications (i.e. MS Outlook™) the user chooses the contact and number then selects ‘dial’ as on screen option, the software then sends the request to the telephone system over the LAN (PC network), the telephone system then makes a live call from the users AASTRA desk telephone or AASTRA DECT handset.

Team (Function) Key is an AASTRA term used to describe the use of a telephone key (button) that indicates the active use of another extension on the system. A team key allows for easy single key transfer between internal extensions.

TWP ‘Telephony Web Portal’ – is an application suite makes unified and collaborative communications easier (AASTRA 400). TWP is a new and future-generation unified communications and collaboration solution that will help your company leverage from E Commerce, IP and GSM Telephony investments to increase your business performance and efficiency. Available Q4 2011.


Unified Communications - Unified Messaging are terms used to describe productivity application that rounds up email’s, voice mail’s, faxes and instant message and presents them to you in a medium of your choice. Think of it as a centralised ‘Inbox’ whereby received messages can be managed from one application such as MS Outlook.


Virtual Subscriber is a telephony term used to describe a system extension number in system software.

Voice Mail is a standard feature (when enabled) on AASTRA telephone systems that allow callers to leave personal or group voice messages (a company ‘out of office hours’ mail box).  Each mail box can have up to three personal greetings easily recorded by the user.

Voice Mail to email notification allows for the forwarding of recorded messages to be sent to an email account as attached wave files

VoIP or Voice over IP is a communication standard used for the transmission of voice traffic (calls) over a data network and connection of IP telephony, handsets (Desk, Cordless) or Soft-phones. Please refer to IP Telephony for more details.

VPN ‘Virtual Private Network’ is a computer network that uses a public telecommunication infrastructure, such as the Internet, to provide remote offices or individual users with secure access to their organization's network.

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