Welltech Dialogic SS7 Protocols ISUP - Manual (Page 101)

Dialogic ® SS7 Protocols ISUP Programmer's Manual Issue 15
Timer expiry during continuity test call
Timers T27 (waiting for CCR) and T36 (waiting for REL after CCR) are run by
the ISUP module. On expiry, the circuit is reset and the call is released to the
application in the usual way.
Figure 18. Example of a T36 Expiry
RLC
RSC
CCR SZE
REL
RLC RLC
T36 expiry
ISUP
MODULE
USER
APPLICATION NETWORK
Outgoing Circuits
There are two situations where continuity checks on outgoing circuits may
occur:
• When a Circuit seized request (SZE) message is received for an idle
circuit.
• When a continuity check is performed on an outgoing circuit during call
set up.
In order to support continuity checks on idle circuits, the Circuit seized
request primitive is used. This special primitive is not defined by ITU or ANSI
but is used to indicate that the circuit has been seized and the format of this
primitive is described in Section 6.5.4 Circuit Seized Request on page 31 . The
Circuit seized request is sent by the user application to ISUP causing a CCR
message to be sent by the ISUP module to the network.
The application needs to control the continuity checking equipment (the
transceivers) and run timers to determine when a continuity check has failed
and when to initiate a continuity recheck.
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