| Abbreviated Dial | a stored number which can be dialled by entering a short code |
ACD
(Automatic Call Distribution) | a system to distribute calls evenly between a number of connecting telephones |
ADSL
(Asymmetric Digital Subscriber Loop) | a new service allowing permanent data connection and voice to SOHO style users over their existing telephone line wiring |
ARS
(Automatic Route Selection) | a system which chooses the cheapest available network by which to dial a call |
| Automated Attendant | a system which answers incoming calls, playing a greeting message and requesting a response which it uses to route the call to the required destination, offering the opportunity to choose an alternative destination or taking a message if the destination is busy |
| Call Barring | a method of controlling the calls which can be made from a telephone |
| Call Divert / Call Forward | a facility to re-direct an incoming call to another designated telephone |
| Call Intrude | the ability to break into another call |
| Call Pick Up | allowing a telephone to answer a call ringing at another telephone |
| Call Waiting | signalling into a call indicating another call is trying to get through |
| Calling Line Identity | the calling party's number is sent to and displayed at the receiving telephone |
| Camp On | a call waiting that will ring through when the called telephone becomes free |
| CCU | Central Control Unit of a telephone system |
| Centrex | a system where a section of a large exchange can be rented and used as a sub-system where all telephones are extensions of the large system. |
| Chain Dialling | dialling a sequence of memory locations stored in another memory |
Co-ax
Co-Axial cable | a central conductor surrounded by an insulator and metal stranded sheath |
| Conference Call | a single call connecting more than two parties all able to talk to each other |
COS
Class of Service | a set of parameters governing how a telephone can be used |
| CPC | a signal from the exchange to tell the receiving equipment that the caling party has cleared |
CPU
Central Processing Unit | the "brain" of a piece of equipment |
| CRA | Call Routing Apparatus |
| Cross Talk | the interference by a call into other calls |
| CT2 | Cordless Telephone 2 digital cordless telephone standard |
| CTI | Computer-Telepone Integration, allows these devices to operate |
DASS / DASS II
Digital Access Signalling System | protocols used on UK ISDN |
| DCE | Data Communication Equipment |
DDI
Direct Dialling Inwards | a part of the dialled number is passed to the destination equipment and used to route the call to the required telephone |
| DECT | Digital European Cordless Telephone specification |
DID
Direct Inward Dialling | a specific line is set to ring a specific extension |
DISA
Direct Inward System Access | the system answers the incoming call and accepts DTMF dialling from the caller to determine the required destination extension |
DND
Do Not Disturb | prevents incoming calls ringing |
| DPNSS | Digital Private Network Signalling System |
| DTE | Data Terminal Equipment |
DTMF
Dual Tone Multi Frequency | the sending of tone combinations to represent the numbers required |
| PABX | Private Automatic Branch Exchange |
| PAD | Packet Assembler/Disassembler |
| PBX | Private Branch Exchange |
| PCI | Pre Connection Inspection |
| PDN | Private Data Network |
| PIN | Personal Identification Number |
| POT | Plain Ordinary Telephone |
PRI
Primary Rate Interface | 30 bearer channel interface to ISDN |
| Prime Telephone | a domestic telephone which can be connected and operate without the need for additional sources of power or continue to operate if its power source fails |
| PSPDN | Packet Switched Private Data Network |
| PSTN | Public Switched Telephone Network |
| Pulse Dialling | dialling by sending pulses representing the numbers required to the exchange |
| PXML | Private Exchange Master List |
