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NCAUUI 15-13
the Q.931 SETUP message and the terminating DMS-250 switch agency is
not an in-service PRI agency, the NCAUUI request is rejected.
For both cases, the request is denied by the terminating DMS-250 switch by
way of the SCCP CREF message. When the originating DMS-250 switch
receives the SCCP CREF message, the DMS-250 switch builds and sends a
Q.931 RELease message with cause value 21 "Call Rejected", location code
of "Transit" and coding standard of "CCITT" to the originating ISDN user.
NCAUUI Invocation Rejection from the Terminating XPM
If TSCBs are not available at the terminating XPM, the terminating
DMS-250 switch rejects the NCA-TSC request message by way of an SCCP
CREF message. When the originating DMS-250 switch receives the SCCP
CREF message, the DMS-250 switch generates and sends a Q.931 RELease
message with a cause value of 42 "Switching Equipment Congestion,"
location code of "Transit and coding standard of "CCITT".
Transfer of User-to-User Information
After a NCA-TSC has been successfully established, User Information
messages may be sent by either the originating or terminating ISDN users.
After the terminating ISDN user sends the Q.931 CONNect message, the
terminating user can begin sending User Information messages. The
originating ISDN user can only send User Information messages after
receiving the Q.931 CONNect message.
When the DMS-250 switch receives a Q.931 User Information message, the
DMS-250 switch builds and sends an SCCP Data Transfer (DT1) message to
the far end switch. The User-to-User Information Parameter Code of #20 in
the Data Parameter field of the SCCP DT1 message indicates User-to-User
Information. This message is sent by either SCCP user to transparently send
user data across a signaling connection. Once the far end switch receives the
SCCP DT1 message, it generates and sends a Q.931 User Information
message to the far end user.
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
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