AT&T MERLIN LEGEND Installation & Maintenance Manual page 49

System Description
Because DID trunks allow calls to come directly to a telephone
extension, they cannot be pooled. The CO passes the necessary
digits to the system, which delivers the call directly to the dialed
extension.
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; however, different DID
trunks can receive different numbers of digits.
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. Additional leading digits are taken
from the 4-digit trunk number, as programmed. For example, if
the system is setup to match three digits and the CO sends only
two, programming determines which DID trunk number prefix to
add 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 either directed to a predesignated extension, such
as the system operator, or the system sends back a reorder tone
(fast busy).
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
contains the options needed to reach the 3-digit numbers, and
trunk block 2 contains the options needed to reach the 4-digit
numbers (see Appendix K).
1-18 Control Unit