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NCAUUI 15-23
In the case of DAP links failure or transaction time out the second time, a
Q.931 RELease message with cause value of 21 "Call Rejected", location
code of "Transit", and coding standard of "CCITT" is sent to the user who is
requesting the NCAUUI service.
Network Transport
Network transport refers to the establishment, data transfer, and clearing of
NCA-TSCs end to end from the perspective of the network. Both single
switch and two-switch call scenarios must be considered.
Network Transport Using SCCP
The functions of the SCCP are performed by means of the SCCP protocol
between two subsystems which provide the SCCP service to the NCAUUS
Subsystem located above the SCCP layer. Within SCCP there are both
connection oriented and connectionless services. This implementation uses
connection-oriented class 2 service which allows for bi-directional,
in-sequence transport of user-to-user messages by way of a true temporary
signaling connection between two SCCP users. Since NCAUUS is a user of
the SCCP, it has a recommended SSN of 72 (#48).
SCCP for NCAUUS utilizes two SCCP datafillable tables, C7NETSSN and
C7LOCSSN. Since the NCAUUS subsystem only resides on CCS7 Service
Switching Points (SSPs), because it is a point-to-point service, therefore not
requiring datafill in the remaining SCCP tables.
NCA-TSC intranetwork setup and management functions utilizes the
existing SS7 signaling link network. No voice circuits are established from
the originating switch to the terminating switch. NCA-TSCs are setup from
originating ISDN user to terminating ISDN user without using bearer
channels at any point in the TSC path which makes this method truly a
non-call associated implementation.
NCA-TSC Establishment at Originating Switch
NCAUUI is only supported for VNET and FLEXSAC call processing.
Upon receiving a Q.931 SETUP message indicating NCAUUI request, the
DMS-250 switch formulates and sends an ADF DAL Request message to
the DAP based on VNET or FLEXSAC call processing. Note that the ADF
DAL Request message is not triggered by the setting of the Bearer
Capability IE or the Channel Identification IE, the IEs used to initiate
NCAUUI. Rather, it is initiated using call processing for VNET and
FLEXSAC calls.
There are two conditions that determine whether a call is a VNET. First, the
PRIVDIAL field in table CALLATTR must be set to NCS. Second, the
Digital Switching Systems DMS-250 ISDN Reference Manual MWC14 (CSP14)
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