Using “D” Messages for Layer 3• 8-18 •
The H.110 Basic Rate ISDN Board
based on Q.931 it uses many network specific extensions for features such
as conferencing and transferring calls. To use the AT&T Custom Protocol,
the protocol level for the port must be set to “A”.
The details of how to use the H.110 Basic Rate ISDN Board with EKTS,
CACH EKTS, and AT&T Custom Protocol are beyond the scope of this
document and may be found in the XDS Layer 3 ISDN Protocol Software
Reference Manual (251M031).
8.11 Call Processing Errors
Calls do not always progress smoothly. Sometimes there is an error in
dialing, the called number is busy, or no route may be available. It is also
possible for a terminal to request a facility that is not supported or
subscribed to. Switching errors can occur or some other problem may arise
creating an error situation.
In these cases the network will send a PROGress message. This message
will indicate the nature of the problem and for speech or audio calls may
indicate the presence of an inband tone or message. To send a PROGress
message to a terminal, the application would send a command of the form
DPxxPccps, where xx is the B-channel of the call, cc is the cause of the
PROGress message, p is the progress indicator, and s is the signal if any.
As an example, the message DP06P11IB, would indicate that the terminal
trying to place a call on the B1 channel of the fourth port has dialed a busy
number (cause 11). Many ISDN Station sets will display an error message
based on the cause. The “IB” indicates that there is an inband tone present
and that the tone is busy. It is the application’s responsibility to provide the
inband signal using a “CP062” command (see section 9.0).
For ports set as a TE, a response of the form DPxxPccps will indicate that
a problem has occurred. The cause will be indicated by the cc, and the
progress indicator and signal will indicate if any error tones or messages are
available.
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