You are here: CSP Developer’s Guide: Common Channel Signaling > 4 SS7 Call Control for ISUP > UPT/UPA (ITU)
Overview
This section defines UPT/UPA and includes call flows related to these messages.
User Part Test Message: The User Part Test (UPT) message is used to test whether a user part is available on a signaling point, which has been marked inaccessible. The test procedure is initiated when the ISUP receives an MTP STATUS Primitive with cause – "user part unavailability – inaccessible remote user". The ISDN User Part shall send a User Part Test message and start timer that supervises the receipt of a response to the user part test message. All MTP STATUS Primitives with cause – "user part unavailability – inaccessible remote user" are ignored when the timer T4 is running. The timer T4 is stopped when a User Part Available (UPA) or any other ISUP message is received.
User Part Available: When a User Part Test acknowledgment message is received by ISUP, the ISUP sends a User Part Available message in response to the message.
UPT and UPA messages are implemented for ITU/CHINA ISUP, with procedures as recommended by ITU ISUP (Q.764).
.
.
UPT Procedure: Remote User Unavailable
The call flow shows the UPT procedure that is initiated when ‘MTP-UPU — Remote user unavailable’ is received.
UPT Procedure—No Response from Far End
This shows the UPT procedure that is initiated when ‘MTP-UPU – Remote user unavailable’ received, and there is no response from the far end.
