Failing to Connect to the VU by Dialing the VU Access Code in the Local Regeneration Network

Publication Date:  2015-07-25 Views:  108 Downloads:  0
Issue Description
Networking:PSTN---Local regeneration node (eSpace U1980, local gateway)---Central node (eSpace U1980)

An outer-office PSTN user dials the VU access code XXXX4000. The PSTN network sends 4000 to the local regeneration node, the local regeneration node sends 4000 to the central node for VU access, and the VU plays announcements. An intra-office user dials the access code 4000 and the VU plays announcement. The preceding are the normal procedures for the outer-office and intra-office users to access the VU.

Fault description:
An outer-office user dials the VU access code, but fails to access the VU and hears no announcements. An intra-office user dials the VU access code and hears the announcements played by the VU.
Handling Process
Step 1 Run the show tkc command to check the trunk status. The trunk works correctly.

Step 2 Dial another number as an outer-office user and dial a PSTN number as an intra-office user. Both calls are successfully connected, which indicates that the trunk works correctly.

Step 3 Check the prefix 4000 on the local gateway. The prefix 4000 does not exist. Add the prefix 4000 and find that the VU works correctly. The possible cause is that the prefix 4000 was deleted.

Step 4 Check error logs and locate the records about deleting the prefix 4000. This verifies the assumption in the previous step.
  • Operators' user names and command inputs
2013-03-14 10:37:44  25770728   21      Success sho pref dn 6721 miguele
2013-03-14 10:38:48  25777074   21      Fail    config del prefix dn 6459 miguele
2013-03-14 10:39:15  25779845   21      Fail    config del prefix dn 4010 miguele
2013-03-14 10:39:24  25780719   21      Success config del prefix dn 4000 miguele
2013-03-14 10:40:13  25785623   21      Fail    config del prefix dn 6459 miguele
  • Login IP addresses and login/logout time
20admin14172.28.1.105Closed2013-03-14 08:51:062013-03-1411:18:33
21miguele172.32.0.84Closed2013-03-14 09:06:392013-03-1409:10:37
21admin172.30.243.109 Closed2013-03-14 09:44:202013-03-1409:45:55
21miguele172.32.0.141Closed2013-03-14 09:50:092013-03-1411:13:52

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Root Cause
The possible causes are as follows:
  • The VU is incorrectly configured.
  • The trunk is faulty.
As the VU still works correctly for intra-office users, the most possible cause is that the trunk is faulty.
Suggestions
When a call is connected to the local gateway in the local regeneration network, the local gateway first analyzes the call prefix. If an intra-office or VU prefix is detected, the local gateway connects the call to the central gateway. If an outer-office prefix is detected, the local gateway connects the call to the outer-office user. If none of the intra-office, outer-office, and VU prefixes is detected, the local gateway returns a failure message.

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