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An AS5400 IOS voice gateway sends two Progress Indicators (PIs) to the TDM switch, causing a call failure on the TDM switch

Core Issue

Call Flow:
H225 setup     ISDN setup
  with 1 PI    with 2 PIs 

  ------originating gateway (OGW)----->terminating gateway (TGW)---->time-division multiplexing (TDM) Switch

Resolution

Sending two Progress Indicators (PIs) should not cause any call failure. A PI is optional information and can cause problems with busy-tone, ring-back tone, or an announcement but not an actual call failure.

It is fine to have two PIs in one message according to the Q.931 standard, section 4.5.23:

     "The purpose of the Progress Indicator information element is to describe an event which has occurred during the life of a call. The information element may occur two times in a message."

For more information, refer to:


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