Welltech Dialogic SS7 Protocols ISUP - Manual (Page 97)

Dialogic ® SS7 Protocols ISUP Programmer's Manual Issue 15
Unsuccessful continuity test call
When the CCR message is received, a Circuit seized indication (SZE) is sent
to the application as above. In this case, a COT message is received from the
network, indicating that the continuity test was unsuccessful. The call is
released to the application, except that no Release confirmation (RLC) is sent
at this stage. This ensures that the circuit does not go idle because a CCR
message is expected. When the second CCR is received, a Circuit seized
indication (SZE) is sent to the application. Note that the application needs to
be able to handle this primitive in the state where it would normally be
expecting Release confirmation (RLC).
The check loop should be removed when the application receives the Release
indication (REL) and re-applied when the Circuit seized indication (SZE) is
received. Removing and re-applying the loop (rather than leaving it in place
while waiting for the continuity re-check) avoids the possibility that the
continuity check continually fails because the loop was not correctly applied
the first time.
Figure 14. Example of a Continuity Check Request Message Received (Unsuccessful
Continuity Check followed by Successful Continuity Check)
REL
CCR SZE
COT (failure) COT (failure)
RLC
RLC RLC
CCR SZE
REL REL
RLC
ISUP
MODULE
USER
APPLICATION NETWORK
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