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NCAUUI 15-27
NCA-TSC Establishment at Terminating Switch
Upon receipt of an SCCP CR message, the terminating DMS-250 switch
formulates and send a Q.931 SETUP message indicating NCAUUI to the
terminating ISDN user using the TTG received in the SCCP CR message as
an index into table VPNTRMRT. The subsequent address digits that were
received from the DAP at the originating switch is sent as the Called Party
Number parameter.
If table VPNTRMRT or subsequent tables indicate that the TTG is not a PRI
agency, then the NCA-TSC request message is rejected. Also, if the TTG is
a PRI agency that are neither NTMWCPRI or N449PRI variants, the
NCA-TSC request message is rejected. If the TTG is not an in-service PRI
agency, the NCAUUI request is also rejected. In these cases, the terminating
DMS-250 switch sends an SCCP CREF message towards the originating
switch effectively rejecting the NCAUUI request. Once the terminating
DMS-250 switch receives the SCCP CREF message, it builds and sends a
Q.931 RELease with a cause value of 21 "Call Rejected" to the originating
ISDN user.
NCAUUI calls are not routed through table VPNIMTRT. For all NCAUUI
calls attempting to route through table VPNIMTRT, the terminating
DMS-250 switch sends an SCCP CREF message to the originating
DMS-250 switch. When the originating DMS-250 switch receives the
SCCP CREF message, it generates and sends a Q.931 RELease message
with a cause value of 21 "Call Rejected", location code of "Transit", and
coding standard of "CCITT" to the originating ISDN user rejecting the
NCA-TSC request message.
If the terminating ISDN user positively acknowledges the request for
NCAUUI with the Q.931 CONNect message, the terminating DMS-250
switch formulates and send a Q.931 CONNect ACKnowledgment message
to the terminating ISDN user and an SCCP CC message towards the
originating switch. Once the terminating user receives the Q.931 CONNect
ACKnowledgment message, the terminating ISDN user may begin sending
ISDN User Information messages.
If the terminating ISDN user negatively acknowledges the request for
NCAUUI with the Q.931 RELease, RELease COMPlete, or DISConnect
message, the DMS-250 switch sends the appropriate Q.931 message to the
terminating ISDN user and send an SCCP CREF message towards the
originating switch.
If the originating user clears an established NCA-TSC, the terminating
DMS-250 switch receives an SCCP RLSD message. The cause value
included in the originating user's Q.931 RELease message is carried in the
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
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