User`s guide
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Network User Identity (NUI)
The N facility code allows you to include your Network User Identity in the call packet. For
security reasons the PAD echoes each character as an asterisk (*) during the entry of an
NUI. Some X.25 services use the NUI field to pass both a username and password for
validation. For example, if your Username is MACDONALD and your password is ASDF, a
typical CALL command would have the format:
CALL NMACDONA;ASDF-56512120
where the “;” is used to separate the username from the password.
Closed User Group (CUG)
Most X.25 networks support Closed User Groups. They are used to restrict subscribers to
only making calls or receiving calls from other members of the same CUG. The CUG number
effectively provides a form of sub-addressing that is used in conjunction with the NUA to
identify the destination address for a call.
When the G facility code is specified in a CALL packet, it must be followed by the CUG
number. This may be a 2 or 4 digit number. If you are a member of a closed user group,
the network may restrict you to only making calls to or receiving calls from other members
of the same group.
Reverse charging
Reverse charging, specified using the R facility code, allows outgoing calls to be charged to
the account of destination address. Whether or not a call is accepted on a reverse charging
basis is determined by the service provider and by the type of account held by the called
user.
Calling user data
The calling user data field for a normal call may contain up to 12 bytes of user data. If the
first character is an exclamation mark (!), the PAD omits the four byte protocol identifier
and allows the full 16 bytes as user data. The same is true for a fast select call except that
the maximum amount of user data is increased from 124 to 128 bytes.
When entering user data, the tilde character (~) may be used to toggle between ASCII and
binary mode. In ASCII mode data is accepted as typed but in binary mode each byte must
be entered as the required decimal ASCII code separated by commas. For example to enter
the data “Line1” followed by [CR][LF] and “Line2” you would enter:
DLine1~13,10~Line2
Aborting a CALL
An X.25 CALL may be aborted using the X.28 CLR command, by pressing [Enter] or by
dropping DTR from the terminal while the call is in progress. Dropping DTR will also
terminate an established call.
If a call is terminated by the network or by the remote host, the unit returns a diagnostic
message before the NO CARRIER result code. Messages may be numeric or verbose
depending on the setting of the ATV command.
The following table lists the verbose messages and equivalent numeric codes:
Code
Verbose message
1 Unallocated (unassigned) number
2 No route to specified transit network