Welltech Dialogic SS7 Protocols ISUP - Manual (Page 95)

Dialogic ® SS7 Protocols ISUP Programmer's Manual Issue 15
95
6.8.4 Continuity Testing
Incoming circuits
There are two situations where continuity checks on incoming circuits may
occur:
• When a Continuity check request (CCR) message is received for an idle
circuit.
• When a continuity check is performed on an incoming circuit during call
set up.
In order to support continuity checks on idle circuits, the Circuit seized
indication (SZE) primitive is used. This primitive is not defined by ITU or
ANSI but is used by the ISUP module to indicate that the circuit has been
seized and the format of this primitive is described in Section : 6.6.4 Circuit
Seized Indication on page 60 . The Circuit seized indication is sent by ISUP to
the application to indicate that the circuit is in use but the call cannot be
routed at present.
On receipt of the Circuit seized indication, the application should mark the
circuit as being busy so that it is not available for selection for an outgoing
call). One way of achieving this would be to introduce a “circuit seized” state
in the application. The application should remain in this state until either a
Setup indication is received (in which case the call should proceed as normal)
or else a Release indication is received (in which case the call is released as
described in Section : 6.8.1 Call Clearing Procedure on page 90 ).
The following subsections show a number of different example scenarios
where a continuity check is made on an incoming circuit.
See Section 8.3: Configure Timers Request on page 136 for details.