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DID-TRK (Direct Inward Dial Trunk)
Issue 1 June 2005 899
DID Trunk Operation
The DID port receives three to seven digits from the CO that are used to directly connect an
outside caller to the called station without assistance from an attendant. For each call, the CO
switch signals the system by opening and closing individual DID loops (one of the eight ports),
causing the starting or stopping of loop current.
DID Trunk Testing
The system uses technician-invoked tests of on-board circuitry to diagnose the health of the
trunk. These are described in the following sections. Additionally, in-line testing which can
generate errors, is performed while a call is in progress. See the Error Log table for a
description of these errors. These errors may be reproduced by placing a call on the trunk and
checking the Hardware Error Log.
Problems detected during signaling may be caused by off-board faults in the CO switch or
connections for which a Warning alarm is raised.
Before a maintenance test can be run on a port, the port must be idle. If an incoming call seizes
a port that is being tested, the test will abort and the incoming call will proceed.
For transmission and signaling standard specification, refer to Digital PBX Standards, RS4648
.
Ports Out-of-Service without Errors or Alarms
A common trouble on DID trunks that produces no errors or alarms occurs when the CO busies
out (disconnects) the port. This situation occurs when the CO thinks there are problems with the
DID port. In this case, no incoming calls will be possible through this port. This may result in
complaints from outside callers trying unsuccessfully to call in. This problem can be diagnosed
by listing measurements on lightly used trunks. If a particular port is detected as idle, a call to
the CO will be necessary to get the connection back in service.
Error Log Entries and Test to Clear Values
Table 307: DID Trunk Error Log Entries
Error
Type
Aux
Data
Associated
Test
Alarm
Level
On/Off
Board
Test to Clear Value
0 (a
) 0 Any Any Any test port location sh r
1
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