Welltech Dialogic SS7 Protocols ISUP - Manual (Page 102)

Section 6 Interface to Application
102
The application must run all the timers associated with the continuity check
and perform the appropriate actions on expiry. For ITU ISUP, the timers are
as follows:
Timer Value Cause for initiation Normal
termination
Action on expiry
T24 <2
seconds
When the Circuit
seized request (or the
Setup request for a call
where a continuity
check is to be
performed) is sent. At the receipt
of backward
check tone. Remove the transceiver, send
Continuity request with the
Continuity indicators set to
continuity check failed and
start T25 or T26 (as
appropriate). If a Setup
request had been sent, the
outgoing call should be
retried on another circuit.
T25 1-10
seconds
When continuity check
failure is detected after
sending a Setup
request. - Send Circuit seized request,
apply the transceiver, and
start T24.
T26 1-3
minutes
When continuity check
failure is detected after
sending a Circuit
seized request. - Send Circuit seized request,
apply the transceiver, and
start T24.
See Section : 8.3 Configure Timers Request on page 136 for details.
The following subsections show a number of different scenarios where a
continuity check is made on an outgoing circuit. In each case, the application
initiates the test by sending either a Setup request or a Circuit seized request
(depending on whether the continuity check is being performed during normal
call set up or as a continuity test call), applying a transceiver to the circuit to
generate the tone, and starting timer T24(waiting to send COT on receipt of
backward check tone). The Nature of connection indicators parameter in the
Circuit seized request or Setup request must have the Continuity check
indicator set to “continuity check required on this circuit”. If the application
detects that the backward check tone was received correctly, this indicates
that the continuity check was successful.