Using “D” Messages for Layer 3• 8-4 •
The H.110 Basic Rate ISDN Board
DPxx CALL PROCeeding
DPxxP PROGress
DRxx RELease or RELease COMplete
DSxx SETUP
DXxx STATus
DYxx REGister
Because of the fact that the required information elements in specific
messages are not identical for the network and terminal or user side, the
argument details are different of NT and TE ports. A complete list of
messages and arguments can be found in section 5.4.
To further simplify the application interface, the board will automatically
send an acknowledgment message. A CONNect ACK is sent where needed
in response to a CONNect message. A RELease is sent in response to a
DISConnect, and a RELease COMplete is sent in response to a RELease
message. A SETUP ACK or a CALL PROCeeding message is sent in
response to a SETUP message from a terminal.
The on board firmware normally hides call references from the application.
Calls are instead associated with B channels. If incoming calls do not have
a B channel assignment, the board will make that assignment. However,
when the association of a call and a B channel is not maintained, as in the
case when a call is placed on hold, the call reference is passed on to the
application so that it can be used to track the calls progress or be used to
retrieve the call. Call references are used more extensively with EKTS and
CACH EKTS.
The “D” message set provides the application with a simple interface that
gives the application complete control of the call but frees it and the
programmer from being forced to deal with the details of coding Q.931
messages.
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