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Slow Connection Setup When the SoftCo Connects to the R2 Trunk in IMS Scenarios

Publication Date:  2015-07-15 Views:  286 Downloads:  0
Issue Description
When a PBX user places an outgoing call through the IMS network, call setup takes a long time.
Handling Process
Step 1 When the calling party dials the number of the called party, the calling party does not add # at the end of the called party's number. As a result, the PBX does not send # to the SIP gateway. It is difficult to determine whether all the digits of the called party's number are sent because signaling with # included is the same as signaling without # included.

Step 2 Change the maximum and minimum number lengths of the called number. (This approach is preferred if the called number length can be identified.)
  • Step 3 After the number length is changed, field engineers found that calls cannot be made. Capture the logs and analyze the details. It is found that the names of From and To fields are incorrect and the calling number format is invalid. Based on the code analysis, such a fault results from one of the following three circumstances:
  • The SoftCo mode is not set to IMS.
  • The user is not associated with a registration group.
  • The calling number type in IMS software parameters is not set to global. Run the show command.
  • The command output shows that this user is associated with a registration group and that the calling number type is set to global. Conclude the failure reason.
  • After several times of number analysis, the calling number is changed As a result, the associated registration group cannot be located. Therefore, this user cannot make outgoing calls.
Step 4 Change the minimum number length to 0 and the maximum number length to the same as the length of the called number. In this way, the wait time for SIP trunks is shortened.

Root Cause
The possible causes are as follows:
  • According to R2 signaling, it takes a long time (approximately 11 seconds) from the time when the SoftCo receives the last digit of the called number to the time when the SoftCo receives the address complete message (ACM).
  • According to the SIP trunk logs, the SoftCo waits additional five seconds after receiving the last digit of the called number.