Specifications

VMMI Programming Exercises
Printed in the USA Page 17 GCA39-082 Rev 2, Issue 9/01
Exercise 9: DID Block Programming
Pre-Setup Discussion
In this exercise, you will:
• Create a DID Block Translation table.
• Test the table to see if translation takes place and the proper station rings.
DID is Direct Inward Dialing. You can dial inside a company directly without going through the
attendant. This feature used to be an exclusive feature of Centrex. It can now be provided by
virtually all modern PBXs and some modern hybrids, but you must connect via specially
configured DID lines from the local central office.
A DID trunk is a trunk from the CO that passes the last two to four digits of the listed directory
number to the telephone system. The phone system can use the digits verbatim, or modify them
through phone system programming to be the equivalent of an internal extension.
NOTE: DID is different from a DIL (Direct-In-Line) where a standard, both-way central office trunk is
programmed to always ring a specific extension of hunt group. DID lines cannot be used for outdial
operation, since there is no dialtone offered.
A DID rule of thumb is for every 10 numbers provided from the telephone company, a hardware
circuit is required (1 pair). For example if there were 50 numbers provided, than the telephone
company typically requires a minimum of 5 circuits. Most telephone companies reserve the right
to review the quality of service and require additional circuits be added.
This service is provided over T-1 circuits or a DID board. The following line drawing illustrates
the wiring required.
Telephone Compan
y
Twenty Numbers T
NNN-NN00 R
NNN-NN19 T
R
Comdial System with T-1
or DID board