ISDN messages convey information between applications
and ISDN drivers. An ISDN message is sent in an
The control portion contains a
header; message parameters (as described in
Section D4isdn manual pages in Section D4isdn manual pages)
are coded in the control portion
following the isdn_msg_hdr:
The messages in this section are defined by SCO but are
based on those defined in the CAPI 2.0 specification.
For more information on the CAPI Association, see
their web site:
Communication between an application and the ISDN
driver always follows this general protocol:
Every message is always followed by a corresponding reply.
A message from an application to the ISDN driver is
called a REQUEST, and the appropriate answer from the
driver is called a CONFIRMATION. On the other side, a
message originating from the ISDN driver is called an
INDICATION, and the corresponding reply from the
application is called a RESPONSE. This naming
convention is reflected in the message name suffixes:
_REQ, _CONF, _IND, _RESP.
Each message contains a message number. The ISDN
driver will always return the number used in the
REQUEST message in the corresponding
CONFIRMATION. Applications may choose unique message
numbers to identify message correlations before interpreting
incoming messages. INDICATIONs from the
ISDN driver should be numbered such that an
application is guaranteed to get different message numbers for
every incoming INDICATION.
An application is not allowed to send RESPONSE
messages without receiving an INDICATION. The
ISDN driver should ignore these illegal messages.
SCO ISDN messages are implementations of messages
defined in the
CAPI (Common ISDN) Version 2.0; for more
information, see the CAPI Association web site.
The following list correlates CAPI and