Welltech Dialogic SS7 Protocols ISUP - Manual (Page 104)

Section 6 Interface to Application
Unsuccessful continuity test call
The continuity test is initiated as in the previous example. If the continuity
check is unsuccessful, a Continuity request is sent indicating failure and timer
T26 (waiting for sending CCR on subsequent COT failure) should be started
by the application. The transceiver should be removed at this point. On
expiry of this timer, the continuity test should be re-initiated on the same
circuit by sending a Circuit seized request, applying the transceiver, and
starting timer T24 (waiting for sending COT on receipt of backward check
tone).
Removing and re-applying the transceiver (rather than leaving it in place
whilst waiting to perform the continuity re-check) avoids the possibility that
the continuity check may continually fail due to the fact that the transceiver
was not correctly applied initially.
Figure 20. Example of a Continuity Check Request Message Sent (Unsuccessful
Continuity Check Followed By Successful Continuity Check)
104
SZE CCR
SZE
REL REL
RLC RLC
CCR
COT (failure) COT (failure)
COT (success) COT (success)
ISUP
MODULE
USER
APPLICATION NETWORK