As an example of DID processing, say that employee A has an external phone number 538-1000 and an extension number 1000. Employee B has a phone number 538-9999 and an extension number 9999.
The steps for completing calls to employees A and B are as follows:
Employee A’s client dials 538-1000.
The CO serving employee A’s company identifies the digits 538 (the common prefix for all phone numbers to that company) and seizes Trunk 1 in the trunk group assigned the digits 538.
The CO passes the digits 1000 to the communication server at employee A’s company.
The communication server identifies the digits 1000 as employee A’s extension number and sends the call to employee A’s extension.
Employee A’s phone rings and employee A answers.
Meanwhile, employee B’s client dials 538-9999.
The CO identifies the digits 538 and seizes Trunk 2 in the trunk group assigned the digits 538.
The CO passes the digits 9999 to the communication server.
The communication server identifies the digits 9999 as employee B’s extension number and sends the call to employee B’s extension.
Employee B’s phone rings and employee B answers.
While employees A and B continue to talk, Trunks 1 and 2 in the 538 trunk group cannot accept any more calls, so another call beginning with the digits 538 seizes yet another trunk in the trunk group.
