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UPT/UPA (ITU)

Overview

This section defines UPT/UPA and includes call flows related to these messages.

Definitions

UPT

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.

UPA

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).

Call Flows

Normal Call Flow for UPT/UPA

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Call Flow for UPA Timeout

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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.

See Integrated Services Digital Network User Part.
See Message Transfer Part.
See Integrated Services Digital Network.
International Telecommunications Union (UN)
ITU-TSS Publication on Signaling Procedures (ISUP)