Using “D” Messages for Layer 3
• 8-11 •
The H.110 Basic Rate ISDN Board
8.5 Directory Numbers
Each B-channel has a default directory number associated with it. These
numbers are set using the “SD” command (see section 4.3). This number
is a seven digit number. On TE ports, it is used for the calling number
element in the SETUP message for calls originating from the port. If no
number is defined for the default, the calling number element will be absent
from the SETUP message. For NT ports, the directory number is used for
the default called number element in SETUP messages for calls originating
from the board and terminating on the terminal. If the application wishes
to use a number other than the default, this can be encoded in the “DS”
message after the calling number with a “/” as a separator.
8.6 Display Text
Many ISDN terminals have the ability to display several lines of text. This
text can contain information about the caller, the status of the call, or
features. Text can be sent to a terminal in an INFOrmation message or it
can be included as an information element if another message. Most
displays have one or two lines of twenty characters and this has been
assumed for the purposes of the “D” message set. When text information
is sent to the a port set as a TE, this text will be passed on to the application
in one or more “D” messages.
Text can be sent to a terminal in several ways using “D” commands. The
simplest way for one line of text to be sent is with a “DI” command of the
form
DIxxT(text)
, where xx is the B-channel and (text) is text of up to 20
characters. If there is no call currently associated with the B channel, the
INFOrmation message will be sent without a call reference. However, if
a call is present, the message will be sent with a call reference and will be
associated with the call. This may affect how the terminal displays the text.
To send multiple lines of text, each line can be set up using a command of
the form
DTxxL1(text)
for the first line and
DTxxL2(text)
for the second
line. This will place text in a buffer. The text can then be sent with a
command of the form
DIxxB
.