AT&T MERLIN LEGEND Release 2.0 Equipment And Operations Manual page 146

Lines and Trunks
With DID service, the customer reserves blocks of DID numbers from the local
telephone company. The DID numbers should correspond to the extension
number for an individual, a calling group, or a Remote Access or pool dial-out
code.
CAUTION:
DID numbers that correspond to pool dial-out codes (or facility access
codes) can be used to evade toll restriction, leading to toll abuse
and/or fraud. (See Customer Support Information in the front of this
book for more information on security.)
The system can receive 1- to 4-digit extension numbers over the DID trunks.
The number of digits received on a specific DID trunk is always the same for
that trunk or for the trunks in a particular DID trunk block; however, different DID
trunks (or trunk blocks) can receive different numbers of digits.
Because DID trunks allow calls to come directly to a telephone extension, they
cannot be pooled. The telephone company's CO passes the necessary digits
to the system, which delivers the call directly to the dialed extension.
If the extension numbers used in the system are fewer than four digits but the
CO sends four, the system can be programmed to ignore the leading digit(s).
For example, if the DID number sent by the CO is 2157, the extension numbers
the system can access are 57, 157, or 2157. System programming determines
the proper extension number to connect.
The system also can be programmed to match more digits than are received
from the CO. For example, if the system is set up to match three digits and the
CO sends the number 24, the system might insert a 9 in front of the 24 (resulting
in the number 924) to complete the match and connect the call.
No routing of calls is made until the designated number of digits is received.
Incoming DID numbers that don't match a valid extension are directed to a
predesignated extension, such as the system console, or the system can be
programmed to send back a reorder tone.
Options are assigned to blocks of DID trunks. A maximum of two blocks of DID
trunks is allowed. Each block can be configured to match the system
numbering plan. For example, the system could have both 3- and 4-digit
extension numbers. Trunk block 1 could contain the options needed to reach
the 3-digit numbers and trunk block 2 could contain the options needed to
reach the 4-digit numbers,
3-12 Direct Inward Dialing (DID) Lines/Trunks