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Appendix A - Call Control Scenarios
409
Non-Call Associated Signaling (NCAS)
NCAS allows users to communicate by means of user-to-user signaling without
setting up a circuit-switched connection (it does not occupy B channel
bandwidth). A temporary signaling connection is established and cleared in a
manner similar to the control of a circuit-switch connection.
NOTES: 1.
This feature is supported for the 5ESS protocol only
2. For more on NCAS, refer to Technical Reference 41459, AT&T
Network ISDN Primary Rate and Special Application Specification.
Since NCAS calls are not associated with any B channel, applications should
receive and transmit NCAS calls on the D channel line device. Once the NCAS
connection is established successfully, the application can transmit user-to-user
messages using the CRN associated with the NCAS call. The Dialogic software
and firmware support 16 simultaneous NCAS calls per D channel.
The following figures provide line diagrams that illustrate the operation of the
NCAS feature.
Network
User
Setup
Connect
Figure 9. User-Accepted Network-Initiated NCAS Request