Welltech Dialogic SS7 Protocols ISUP - Manual (Page 106)

Section 6 Interface to Application
Unsuccessful continuity check during call set up
Following an unsuccessful continuity check during normal call set up, timer
T25 (waiting to send CCR and repeat continuity check) should be started by
the application. On expiry of the timer, the application should initiate the
continuity recheck by sending a Circuit seized request, applying the
transceiver, and starting T24 (waiting for sending COT on receipt of backward
check tone).
Figure 22. Example of a Continuity Check Success during Outgoing Call Set Up
106
RLC RLC
REL REL
IAM IAM
COT (failure) COT (failure)
CCR CCR
ISUP
MODULE
USER
APPLICATION
ANSI operation
In ANSI ISUP, the Loop Back Acknowledgement indication (LPA) message is
received after the CCR message is sent to indicate that the other end has
connected the loop. On receipt of the LPA, the sending side should start
sending the check tone.
The ANSI ISUP standard defines a timer, Tccr, which is used to wait for the
LPA message. This timer is implemented in the ISUP module as timer T104
(waiting for LPA). Timer T104 may optionally be run. This timer is controlled
by a circuit group option (ISPGOP_TCCR_CTRL), if this option is set, the ISUP
module will wait for an LPA message and on its receipt shall pass on the LPA
message before changing to an appropriate state. If the option is set, on
T104 expiry, the circuit will be reset.
NETWORK