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Direct Inward Dialing (DID, also called DDI in Europe) is a feature offered by telephone companies for use with their customers' PBX systems, whereby the telephone company (telco) allocates a range of numbers all connected to their customer's PBX. As calls are presented to the PBX, the number that the caller dddialed is also given, so the PBX can route the call to the desired person or bureau within the organization. A Private Branch eXchange (PBX) is a telephone exchange that serves a particular business or office, as opposed to one that a common carrier or telephone company operates for many businesses or for the general public. ...
A telephone company (or telco) provides telecommunications services such as telephony and data communications. ...
A telephone number is a sequence of decimal digits that uniquely indicates the network termination point. ...
The person who (or device that) initiates a telephone call over the public switched telephone network is the calling party. ...
Developed by AT&T in the 1960s, patterned upon the earlier IKZ service of the Deutsche Bundespost, this feature enables companies to have fewer lines than extensions, while still having a unique number for each extension, callable from outside the company. AT&T Inc. ...
This article needs copyediting (checking for proper English spelling, grammar, usage, tone, style, and voice). ...
In telecommunication, the term trunk has the following meanings: In a communications network, a single transmission channel between two points that are switching centers or nodes, or both. ...
A telephone extension is an internal telephone line attached to a PBX or Centrex system. ...
By way of example, each extension of the PBX system may be assigned a seven-digit external telephone number, with a fixed four- or five-digit prefix. Someone who knows the internal extension of his/her correspondent can dial the seven-digit number and be connected directly to the person called, bypassing the operator or PBX auto-attendant. A telephone operator at work on a private switchboard A telephone operator is either a person who provides assistance to a telephone caller, usually in the placing of operator assisted telephone calls such as calls from a pay phone, collect calls (called reversed-charge calls in the UK), calls which...
In telephony, an automated attendant (also auto attendant or auto-attendant, or sometimes autoattendant or AA) system allows callers to be automatically transferred to a users extension without the intervention of a receptionist. ...
This system is also used by fax servers. Instead of an exchange at the end of the 234 000 line, a computer running fax server software and fax modem cards uses the last three digits to identify the recipient of the fax. This allows 1000 people to have their own individual fax numbers, even though there is only one 'fax machine'. A fax server is a set of software running on a server computer which is equipped with one or more fax-capable modems attached to telephone lines (or, more recently, software modem emulators which use T.38 (Fax over IP) technology to transmit the signal over an IP network). ...
When people give out their work number and say it's a "direct line", often what they mean is that it's a DID number.
DID (DDI) and VoIP aka "Call Through"
"DID" numbers have particular relevance for VoIP communications. In order for people connected to the traditional PSTN network to call people connected to VoIP networks, DID numbers from the PSTN network are obtained by the administrators of the VoIP network, and assigned to a gateway in the VoIP network. The gateway will then route calls incoming from the PSTN across the IP network to the appropriate VoIP user. Similarly, calls originating in the VoIP network will appear to users on the PSTN as originating from one of the assigned DID numbers. An overview of how VoIP works A typical analog telephone adapter for connecting an ordinary phone to a VoIP network Ciscos implementation of VoIP - IP Phone Voice over Internet Protocol, also called VoIP, IP Telephony, Internet telephony, Broadband telephony, Broadband Phone and Voice over Broadband is the routing of...
The public switched telephone network (PSTN) is the network of the worlds public circuit-switched telephone networks, in much the same way that the Internet is the network of the worlds public IP-based packet-switched networks. ...
In telecommunications, the term gateway has the following meanings: In a communications network, a network node equipped for interfacing with another network that uses different protocols. ...
DID numbers can be purchased in bulk from a Competitive Local Exchange Carrier. There are also a number of DID resellers offering DID numbers for individuals and small enterprises. A Competitive Local Exchange Carrier (CLEC), in the United States, is a telecommunications provider company (sometimes called a carrier) that competes with other, already established carriers (generally the incumbent local exchange carrier (ILEC)). Local exchange carriers (LECs) are divided into incumbent (ILECs) and competitive (CLECs). ...
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