Northern UTA220/UTA220k - Manual (Page 78)

12-2
UTA220/UTA220k
D-Channel X.25
ESTABLISHING AN X.25 SESSION
Before using the TA for X.25 communications on the
D-channel, the user must subscribe to the ISDN D-packet
service. If the user is subscribed to the D-packet service, a
connection is automatically established between the TA and
the ISDN packet handler when the TA is first powered up. This
is known as the D-channel X.25 link connection. Once the TA
is connected to the ISDN packet handler, the X.25 PAD is used
to make an X.25 virtual connection to a specific remote host
or device. The connection is called “virtual” because it is not
a direct physical connection; a transmission path is created for
each call and held until communications are completed and the
connection is disconnected.
The following explains how an X.25 virtual connection
(session) is established and disconnected, as well as some of
the activities performed during the X.25 session.
Initialize the PAD
When the TA is first powered up, the TA is in the AT command
mode. There are three AT commands that the TA supports to
initialize the PAD:
ATDD
AT@P1 = P
AT@P1 = D
Once the PAD is initialized, the PAD prompt character *
displays and the PAD is in the PAD command mode.
ATDD Command
The ATDD command is valid for initializing the PAD only
when the D-channel X.25 link is established. If the ATDD
command is entered when the D-channel X.25 link is not
established, the TA responds with ERROR and remains in the
AT command mode.
AT@P1=P or AT@P1=D Command
The AT@P1=P or AT@P1=D command initializes the PAD
automatically when the TA is powered up. If the D-channel
X.25 link is not established when the TA is powered up, the
PAD is initialized to the PAD command mode. Likewise, if
the D-channel link is connected when the TA is powered up,
the PAD is initialized to the PAD command mode, just as
though an ATDD had been executed.