Continuity recheck

The application initiates a continuity recheck by invoking ISUPStatusReq with the event type of CONTCHK. This causes the ISUP layer to send a continuity check request message (CCR) to the far exchange.

The far exchange sets the indicated circuit in a loop back condition and acknowledges with a loop back acknowledgment message (LPA). Upon receipt of this message, the ISUP layer issues a status indication (EVTSITSTAIND) to the application with event type of LOOPBACK. The application can then perform the continuity check.

If the continuity check fails, the application can invoke ISUPStatusReq with the event type of CONTREP.

Note: The BICC variant does not support continuity checks or rechecks.

The following illustration shows an outgoing continuity recheck failure:

If the continuity check is successful, the application can release the connection by following the procedures for outgoing release as described in Clearing connections. The following illustration shows an outgoing continuity recheck success:

When a continuity check request message (CCR) is received from the far exchange, the ISUP layer issues a status indication (EVTSITSTAIND) with event type of CONTCHK to the application. The application can set the specified circuit into a loop back condition and acknowledge the request by invoking ISUPStatusReq with event type of LOOPBACK.

If the continuity test fails, the far exchange reports the results with a continuity message (COT). The ISUP layer reports the results to the application as a status indication (EVTSITSTAIND) with event type of CONTREP.

The following illustration shows an incoming continuity recheck failure:

If successful, the far exchange transmits a release message (REL) as a release indication (EVTSITRELIND) to the application. The application follows the normal procedures for a far exchange initiated release as described in Clearing connections.

The following illustration shows an incoming continuity recheck success: