# List of telephony terminology

This is a list of telephony terminology and acronyms which relate to telephony networks.
* Top
* 0–9
* A
* B
* C
* D
* E
* F
* G
* H
* I
* J
* K
* L
* M
* N
* O
* P
* Q
* R
* S
* T
* U
* V
* W
* X
* Y
* Z

## A

* Advanced Intelligent Network, (AIN), see also IN or Intelligent Network
* Automatic number announcement circuit (ANAC)
* Automated Attendant
* ACD - Automatic Call Distribution
* Articulation score

## B

* Blue box - a device that was used to bypass the normal long-distance call switching tones typically used to obtain free calls.

## C

* Call originator - (or calling party, caller or A-party) a person or device that initiates a telephone call by dialling a telephone number.
* Call waiting - a system that notifies a caller of another incoming telephone call by sounding a sound in the earpiece.
* Called party - (or callee or B-party)
* Caller
* Calling party
* Conference call (multi-party call)
* COCOT
* Cut – unexpected, and usually sudden, termination of call, line or service

## D

* Dial peer
* Dial tone
* Distribution frame
* Dual-tone multi-frequency signaling (DTMF)

## E

* Emergency telephone number
* End instrument
* Engset calculation
* Erlang unit

## F

* Fax - (contraction of facsimile) a device connected to the telephone network to enable documents to be scanned and sent to a receiving fax machine
* Frame - A distribution frame, a set of open wiring racks where circuits are cross connected to trunks and equipment

## H

* Handoff
* Handover
* Help desk
* Howler tone (see ROH tone)
* Hunt Group

## I

* Infrastructure
* Intelligent Network (IN)
* Interface functionality
* Inside plant
* Intelligent Network Interface Device (iNID) - replaces the Network Interface Device outside a subscriber's house like when customers subscribe to AT&T's U-verse brand of services.
* Interactive voice response (IVR)
* ISDN User Part (ISUP)

## L

* Line
* Local loop
* Long-distance operator

## O

* On-premises wiring
* Operator assistance
* Outside plant

## P

* Patch-through access
* Permanent signal
* Person-to-person
* Plain old telephone service, or "POTS"
* Public Switched Telephone Network (PSTN)
* Pupinization

## R

* Receiver Off-Hook tone (ROH)
* Red telephone box
* Red box
* Regional Bell Operating Company (RBOC)
* Ringer equivalency number (REN)
* Ringing signal
* Rural radio service

## S

* Smartphone
* Station-to-station
* Signalling System 7 (SS7)

## T

* Tandem signaling
* Tandem switch
* Transaction Capabilities Application Part (TCAP)
* Telemarketing
* Telephone
* Telephone booth
* Telephone call
* Telephone card
* Telephone directory
* Telephone exchange
* Telephone tapping
* Teletraffic engineering
* Time Division Multiplexing (TDM)
* Trap and trace
* TWX

## V

* Vertical service code
* Voicemail
* Voice over Internet Protocol (VoIP)

## W

* Western Union
* Wide Area Telephone Service (WATS)
* WATS line
* Wireless network
* Wireless Telephony Applications Interface (WTAI)
* Wi-Fi

## Z

* Zenith number

## Acronyms

| Acronym | Name | Notes |
| 1ESS | Number 1 Electronic Switching System (Alcatel-Lucent) | US |
| 1FR | Flat rate service | US |
| 2G | second-generation mobile telephone | |
| 2.5G | Enhanced 2G mobile telephone | |
| 3G | third-generation mobile telephone | |
| 4ESS | Number 4 Electronic Switching System (Alcatel-Lucent) | |
| 4WTS | Four-wire termination set | US |
| 5ESS | Number 5 Electronic Switching System (Alcatel-Lucent) | |
| ACD | Automatic Call Distribution/Director | |
| ACTS | Advanced Coin Telephone Service | US |
| ADSL | Asymmetric Digital Subscriber Line | |
| ANI | Automatic Number Identification | US |
| AMA | Automatic Message Accounting | US |
| BOK | Unblocking | UK |
| CCIS | Common Channel Interoffice Signaling | |
| CID | Caller ID | |
| CLEC | Competitive Local Exchange Carrier | US |
| CLI | Caller Line Identification | Europe |
| CLID | Caller Line ID | UK |
| CTI | Computer telephony integration | |
| COSMOS | Wire records | |
| DDCO | Direct Dial Central Office (Opposite of DID) | US |
| DDD | Direct Distance Dialing | US |
| DDI | Direct Dialing In | UK |
| DECT | Digital Enhanced Cordless Telecommunications | |
| DID | Direct Inward Dialing | US |
| DMS | Digital Multiplex System (e.g. DMS-100) | Can |
| DNIS | Dialed Number Identification System | US |
| DSL | Digital subscriber line | |
| DTMF | dual-tone multi-frequency | |
| FDM | Frequency-division multiplexing | |
| GPRS | General Packet Radio Service | |
| GSM | Global system for mobile communications | |
| GST | Ground Start Trunk | US |
| IDDD | International Direct Distance Dialing | US |
| IDF | Intermediate distribution frame | US |
| ILEC | Incumbent Local Exchange Carrier | US |
| ISD | International Subscriber Dialing | UK and India |
| ISDN | Integrated Services Digital Network | |
| IVR | Interactive Voice Response (a.k.a. VRU) | |
| KSU | Key Switching/System Unit | US |
| LST | Loop Start Trunk | US |
| MDF | Main Distribution Frame | |
| MF | Multi-frequency | US |
| PABX | Private Automatic Branch eXchange | Europe |
| PBX | Private Branch eXchange | US |
| PMBX | Private Manual Branch eXchange | UK |
| POTS | Plain Old Telephone Service | |
| PSTN | Public Switched Telephone Network | |
| RCMAC | Recent Change Memory Administration Center | US |
| REN | ringer equivalency number | |
| SMS | Short Message Service (i.e. text messages) | |
| SF | Single Frequency supervision tone (2600) | US |
| SIP | Session Initiation Protocol | US |
| SP Lock | Unlocking | UK |
| SS7 | Signaling System 7 | |
| STD | Subscriber trunk dialling | UK and India |
| T-CXR | T-carrier (e.g. T-1) | US |
| TAPI | Telephony Application Programming Interface | |
| TR | Tip and ring | US |
| TSPS | Traffic Service Position System | |
| TXE | Telephone eXchange Electronic | UK |
| UAX | Unit Automatic eXchange | UK |
| VoIP | Voice over Internet Protocol | US |
| WAP | Wireless Application Protocol | |
| WATS | Wide Area Telephone Service | US |
| WTAI | Wireless Telephony Applications Interface | |