5.10.1. Inbound Continuity Check

When a continuity check request is received from the network, the GCEV_EXTENSION event is sent to the application with the value of the S7PARM_CONTCHECK_TYPE parameter (as described in Section 5.10, Continuity Check) set to S7RV_CC_INBOUND. Upon receipt of this event, the application must do the following:

• Save, if necessary, the current time slot assignment of the current line
• Mark the current line as unavailable for outgoing calls until a GCEV_EXTENSION event is received with the ext_id field set to S7_EXT_CONTCHECK_END
• Put the line in loopback for the continuity test by calling gc_Extension( ) with an ext_id value of S7_EXT_APPLYLOOPBACK

Note: If the line is not put in loopback mode, the continuity check will always fail. The gc_Extension( ) function with the ext_id set to S7_EXT_APPLYLOOPBACK puts the line in loopback mode for the purpose of running the continuity check. In ANSI networks, an SS7 LPA message is sent to the network.

When the continuity check process is completed, the application receives a GCEV_EXTENSION event with an ext_id of S7_EXT_CONTCHECK_END.

Note: The gc_Extension(S7_EXT_APPLY_LOOPBACK) function changes the timeslot that the network device is listening to. Therefore, when the continuity test finishes, the application must use the gc_Listen( ) function to restore the timeslot that is being transmitted out of the network interface (that is, the CT Bus timeslot that the network device is listening to).

For the inbound continuity check, the S7PARM_CONTCHECK_TYPE parameter value can be S7RV_CCEND_INBOUND_SUCCESS or S7RV_CCEND_INBOUND_FAILURE. If the continuity check fails (S7RV_CCEND_INBOUND_FAILURE), the application may decide not to use the circuit until a new continuity check completes successfully on that circuit.

Note: In some cases, multiple GCEV_EXTENSION events with an ext_id of S7_EXT_CONTCHECK may arrive on the same line device before a GCEV_EXTENSION event with and ext_id of S7_EXT_CONTCHECK_END is received. This is not an error but an indication that the network is re-checking the same circuit. However, the application must put the line in loopback mode every time.

For continuity check requests received during call setup (the SS7 IAM message), the same rules apply. The application will receive a GCEV_EXTENSION event with an ext_id equal to S7_EXT_CONTCHECK and the S7PARM_CONTCHECK_TYPE parameter value set to S7RV_CC_INBOUND. Thereafter, when the Continuity Check finishes, another GCEV_EXTENSION event with an ext_id of S7_EXT_CONTCHECK_END is received. In the latter case, success or failure of the continuity check process is also indicated by a parameter value of S7RV_CCEND_INBOUND_SUCCESS or S7RV_CCEND_INBOUND_FAILURE. If the continuity check is successful, the application receives a GCEV_OFFERED event following the GCEV_EXTENSION event. If the continuity check is not successful, the application will not be aware of the call attempt.

If an SS7 IAM message is received with a "continuity check performed on previous circuit" indication, the GCEV_OFFERED event is not sent to the application until the call control library receives an SS7 COT message indicating the success of the continuity check.

Note: The gc_Extension(APPLY_LOOPBACK) function changes the timeslot that the network device is listening to. Therefore, when the continuity test finishes, the application must use the gc_Listen( ) function (or dt_listen( ) for a DTI device) to restore the timeslot that is being transmitted out of the network interface (that is, the CT Bus timeslot that the network device is listening to).

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