Global Call SS7 Technology User's Guide for Windows: 5.10.2. Outbound Continuity Check

As for the inbound continuity check, the outbound continuity check can be done outside of any call (Out-of-Call) or as part of an outgoing call (In-Call). However, in the outbound case, since the check is initiated by the application, the procedures for both types of check differ.

Outbound Out-of-Call Continuity Check

When requesting an outbound out-of-call continuity check on a circuit, the line device must be in the Idle state, that is, the circuit must be unblocked and cannot have any active calls. The application can then use the gc_Extension( ) function with an ext_id of S7_EXT_REQUESTCONTCHECK to send an SS7 CCR message to the network.

The application receives a GCEV_EXTENSION event with an ext_id of S7_EXT_CONTCHECK and with a parameter value of S7RV_CC_OUTBOUND to indicate that it can begin the continuity check by connecting the test equipment to the line.

When the continuity check is completed and the result analyzed, the application must call gc_Extension( ) with an ext_id of S7_EXT_SENDCONTCHECKRESULT to communicate the results of the check to the remote party. To achieve this, the application must build a GC_PARM_BLK structure. The set_ID must be S7SET_CONTCHECK and the param_ID must be S7PARM_CONTCHECK_RESULT and the parameter value must be either CONTI_SUCCESS or CONTI_FAILURE.

If the function is called with CONTI_SUCCESS, the continuity check process is finished and the application is notified by a GCEV_EXTENSION event with an ext_id of S7_EXT_CONTCHECK_END and with a parameter value of S7RV_CCEND_OUTBOUND. When the application receives this event, the line can be used for making or receiving calls.

If the function is called with CONTI_FAILURE, the remote side is waiting for a re-check, and therefore the application does not receive a GCEV_EXTENSION event with an ext_id of S7_EXT_CONTCHECK_END.

Outbound In-Call Continuity Check

To request an in-call continuity check, the application must call gc_MakeCall( ) with the continuity_check_indicator field in the S7_MAKECALL_BLK structure set to CCI_CC_REQUIRED, so that the Global Call library sends an SS7 IAM message, with continuity check requested, to the network.

If the continuity check is successful, the application indicates the success to the remote side by calling gc_Extension( ) with an ext_id of S7_EXT_SENDCONTCHECKRESULT and a parameter value of CONTI_SUCCESS. Since the continuity check process is now finished, the application receives a GCEV_EXTENSION event with an ext_id of S7_EXT_CONTCHECK_END with a parameter value of S7RV_CCEND_OUTBOUND. When the application receives this event, the call proceeds in the normal way.

If the continuity check fails, to indicate the failure to the remote side, the application must call gc_DropCall( ) with a cause value of CONTCHECK_FAILED. The call is cleared internally by Global Call and the other side will have no knowledge of the call. The other side only recognizes a failed continuity check test and waits for a re-check.

If a failure result is sent to the other side, the other side will expect a re-check on the circuit. Therefore, another call to gc_Extension( ) with an ext_id of S7_EXT_REQUESTCONTCHECK should be issued by the application, until the continuity check succeeds. Alternatively, the application could reset the circuit using gc_ResetLineDev( ) on the corresponding line device. In this case, the application does not receive a GCEV_EXTENSION event, but receives a GCEV_RESETLINEDEV event corresponding to the gc_ResetLineDev( ) function call.

The GCEV_EXTENSION event with an ext_id of S7_EXT_CONTCHECK_END may be received in two other cases:

In both cases of the GCEV_EXTENSION event with ext_id of EXT_CONTCHECK_END above, the continuity check process is abandoned by the Global Call library. The application should not try to perform the physical continuity test again or try to send any continuity check results because the remote side is not ready to receive the results and the send operation will fail.