Automatic Call Distribution (ACD) basics
24 Communication Manager Guide to ACD Call Centers
Direct inward dialing processing
With Direct Inward Dialing (DID) processing, incoming trunks do not connect the CO
directly to an employee’s phone; instead, the incoming trunks are pooled by the
communication server, and this pool of trunks is then shared by employee phones.
Extension numbers may serve as the final digits of employee phone numbers for incoming
calls. That is the CO may assign a 2- 3- or 4- digit prefix to a trunk group. Then, when a 7-
digit employee phone number is dialed, the call is processed as follows:
1. The CO processes the prefix of the dialed number, and then seizes a trunk in the trunk
group that is assigned that prefix.
2. The CO passes the remaining digits of the dialed number to the communication server.
3. The communication server recognizes the remaining digits as an employee extension
number and sends the call to that extension.
DID processing example
As an example of DID processing, say that Employee A has the external phone number
538-1000 and the extension number 1000. Employee B has the phone number 538-9999
and the extension number 9999.
The steps in completing calls to Employees A and B might be as follows:
1. Employee A’s client dials 538-1000.
2. 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.
3. The CO passes the digits 1000 to the communication server at Employee A’s company.
4. The communication server identifies the digits 1000 as Employee A’s extension
number and sends the call to Employee A’s extension.
5. Employee A’s phone rings and Employee A answers.
6. Meanwhile, Employee B’s client dials 538-9999.
7. The CO identifies the digits 538 and seizes Trunk 2 in the trunk group assigned the
digits 538.
8. The CO passes the digits 9999 to the communication server.
9. The communication server identifies the digits 9999 as Employee B’s extension
number and sends the call to Employee B’s extension.
10. 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 will not
accept any more calls, so another call beginning with the digits 538 will seize yet another
trunk in the trunk group.
