UK ISDN signalling protocol.


A signalling system used to communicate between two adjacent pieces of telecommunications equipment, for example between a telephone system and a router or multiplexer or between two co-located telephone systems. For communication over longer distances DC5 can be converted to AC15.


Data Circuit Terminating Equipment


Digital Control Protocol


Direct Dialling Inwards
A key ISDN feature is the ability to assign individual phone numbers (DDI Numbers) to extensions and departments, enabling callers to dial them directly without having to go through the operator.


Digital Enhanced Cordless Telephony
 - DECT cordless handsets provide wireless communications within an office or company premises. The handsets can be fully integrated with the company phone system, allowing users to make, take and transfer calls securely as they move around the premises.

Delayed Ringing

A feature often used to provide an overflow if the switchboard operator is busy or absent. Incoming calls are sent to the operator but other extensions have delayed ringing, so they will start ringing if the call is not answered after a pre-set time.


Dynamic Host Configuration Protocol
Allows each device on the network to acquire its own unique IP address in order for it to communicate correctly with other devices.

Dial Up

A communications link that connects a terminal and a computer via the Public Switched Telephone Network (PSTN).


Direct Inward Station Access
Provides callers with single-digit access to extensions or ring groups.


The term used for the functions of a collection of components (for example, patch panels, patch cords) used to connect cables.


Digital Private Network Signalling System
A private networking standard developed by BT and other PBX suppliers which allows full feature access to be provided between PBXs in private networks. 2mb circuit which can provide up to 30 digital circuits for network telephone and data systems


Digital Subscriber Line
DSL provides digital data transmission over the wires of a local telephone network. Typically, the download speed of DSL ranges from 128 kilobits per second (kbit/s) to 24,000 kbit/s depending on DSL technology and service level implemented.


Digital Subscriber Line Access Multiplex
A network device, usually at a telephone company central office, that receives signals from multiple customer Digital Subscriber Line connections and puts the signals on a high-speed backbone line using multiplexing techniques.


Digital Signal Processing/Processor
 - A silicon device that uses sophisticated signal manipulation procedures to enhance its quality.


Direct Station Select
 - A button on a terminal that can be used to directly dial a person or extension associated with that button.


Data Terminal Equipment
 - Such as PC, printers, terminals.


Dual Tone Multi Frequency
 - Signalling which is the basis for the operation of pushbutton telephone sets. Dialled numbers are transmitted as tones rather than electronic pulses. This is particularly useful for access to supplementary services (e.g. voicemail and auto attendants).