Digi TransPort User Manual page 345

X.25 parameters
channel operation, ensure that the "LAPD" option is selected. For ISDN B-channel operation or
operation through a synchronous port, select "LAPB". In the case of LAPB and LAPD it is also
possible to specify an interface number. This parameter specifies which LAPB or LAPD
instance to use for the relevant TPAD instance. Select "0" or "1" for LAPB or "0" or "1" for LAPD.
Use backup interface
This section is used to specify a backup interface that will be used automatically if the call to
the primary interface fails. Note that the primary interface will be tried first for every new call
attempt.
X.25 Settings
Default X.25 packet size
This parameter determines the default X.25 packet size. This may be set to "16", "32", "64",
"128", "256", "512" or "1024", but the actual values permitted will normally be constrained by
your service provider.
Answer incoming calls from NUA
This is the NUA that the unit responds to for incoming X.25 calls.
Only answer calls with CUG
The PAD will only answer calls with this Call User Group (CUG) specified.
Use X.25 Call Macro macroname to an ATD command
This parameter specifies the name of an X.25 call macro that is used when an ATD command
is received by the unit. The ATD command is ignored, and a PAD CALL command using the
macro replaces it. The purpose of this feature is to allow non-PAD terminals to use an X.25
PAD network connection. X.25 call macros are set up in the Configuration - Network >
Legacy Protocols > X.25 > Call Macros web page, or by using the macro text command.
Use NUA
This NUA will be used as the calling NUA when an outgoing X.25 call is made.
LCN
The unit supports up to eight logical X.25 channels. In practice, the operational limit is
determined by the particular service to which you subscribe (usually 4).
Each logical channel must be assigned a valid Logical Channel Number (LCN). The LCN
parameter is the value of the first LCN that will be assigned for outgoing X.25 CALLs. The
default is 1027.
For incoming calls, the unit accepts the LCN specified by the caller.
LCN Direction
This parameter determines whether the LCN used for outgoing X.25 calls is incremented or
decremented from the starting value when multiple X.25 instances share one layer 2 (LAPB or
LAPD), connection. The default is "Down" and LCNs are decremented, such as if the first CALL
uses 1024, the next will use 1023, etc. Setting the parameter to "Up" will cause the LCN to be
incremented from the start value.
NUI/NUA selection
If both an NUI and an NUA are included in the call string, this parameter allows the unit to
filter one of these out of the X.25 call request. This can be extremely useful in backup
scenarios. Consider the following example; the unit is configured to do online authorisations
via the ISDN D channel and to fall back to B-channel (if the D-channel host did not respond for
Digi TransPort User Guide 345