Troubleshooting guide

Diagnosing Problems
209
- ARS programming
- Digit Conflict
- Interconnect Restriction
- Far end fault/programming
• If only calls to the central office fail check that the Class Of Service option of Public Network
Access via DPNSS is enabled on the extension making the call and the MSDN trunks.
Loopback Testing on Digital Trunks
You can perform a loopback test on digital trunks to rule out problems with the system hardware.
If two trunks can be successfully looped, and calls made that contain no slips, BERs, or framing
losses, the system is operating properly. The loopback test requires the use of two trunks.
To perform loopback testing:
1. Assign a digital link descriptor to each hybrid (see the Digital Link Descriptors form).
2. Ensure the trunks are the same type. If MSDN will be used, ensure one hybrid is set to A,
and the other is set to B.
3. Configure a valid Trunk Descriptor (see the appropriate CO Trunk Circuit Descriptors form).
4. Configure a valid Trunk Service Assignment (see the Trunk Attributes form), and set the
Absorb field to “0”.
5. Include the trunks in two separate Trunk Groups and routes (see the Trunk Groups and
the ARS Routes forms).
6. Complete ARS programming, using unique leading digits and a valid number of digits to
follow (extension number length). You should be able to make a call from each Trunk Group
back into the switch to a valid extension.
7. Program the Number of Digits to Absorb field, of the ARS Digit Modification Plans form, to
strip away the leading digits.
8. To connect loopback between trunks on a T1/E1 Module or Network Service Unit (NSU),
you have two options:
• Option 1: Set one trunk in Network Termination (NT) Mode and the other trunk in Line
Termination (LT) Mode. You set the line termination mode in the Link Descriptor As-
signment forms of the trunks. Then, connect the trunks with a straight-through CAT5
cable.
• Option 2: If you want to have both trunks in the same mode, you must wire the T1/E1
trunk connectors together as shown in Figure 2.
9. To set up loopback through the DSU card in a DSU cabinet, wire the DB15 connectors
together as shown in Figure 3.
10. Complete calls to confirm there are no errors with the system equipment.