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.\" @(#)tn3270.1 4.6 (Berkeley) 7/27/91
.Nd full-screen remote login to
permits a full-screen, full-duplex connection
gives the appearance of being logged in
Of course, you must have an account on the machine
to which you connect in order to log in.
looks to the user in many respects
Terminal Communication System II.
is actually a modification of the Arpanet
which will, in certain circumstances, interpret and generate
raw 3270 control streams.
Turn on socket-level tracing (for super-user only)
Specify a file to receive network trace data
output (from commands "toggle netdata" and
the default is for output
to be directed to the standard error file.
4994 style transparent mode
data received from the remote
The name of the remote system. If the remote name
is NOT specified, the user will be prompted for a
The port to connect to on the remote system.
attempts to connect to the
23) on the remote machine.
first connects to the remote system, it will negotiate to go into
Part of this negotiation involves telling the remote system what model
emulates a 3278 terminal.
To decide which specific model,
looks at the number of lines and columns on the actual terminal (as
environment variable; see
The terminal (or window in which
window systems) must have at least 80 columns and 24 lines, or
will not go into emulation mode.
If the terminal does have at least 80 columns and at least 24 lines,
the following table describes the emulation:
.Bd -filled -offset center
.Bl -column (rows*columns)
.It minimum_size emulated
.It (rows*columns) terminal
.It -------------- ------------
Emulation of the 3270 terminal is done in the
This emulation involves mapping
3270-style commands from the host
into appropriate sequences to control the user's terminal screen.
.Pa /usr/share/misc/termcap
The emulation also involves simulating the special 3270 keyboard keys
(program function keys, etc.)
by mapping sequences of keystrokes
keyboard into appropriate 3270 control strings.
This mapping is terminal dependent and is specified
.Pa /usr/share/misc/map3270 ,
or in an environment variable
Any special function keys on the
keyboard are used whenever possible.
If an entry for the user's terminal
looks for an entry for the terminal type
uses a default keyboard mapping
The first character of each special keyboard mapping sequence
a control character, or an
If the user types an unrecognized function key sequence,
defined in the user's termcap entry, to the user's terminal
and nothing is sent to the
is invoked without specifying a remote host system name,
it enters local command mode,
plus one additional command:
4994 style transparent mode processing.
command mode may also be entered, after connecting to a host, by typing
a special escape sequence.
has succeeded in negotiating 3270 mode with the remote host, the
escape sequence will be as defined by the map3270 (see
entry for the user's terminal type
otherwise the escape sequence will initially be set to the
(control right square bracket).
While in command mode, any host login session is still alive
but temporarily suspended.
The host login session may be resumed by entering an empty line
in response to the command prompt.
A session may be terminated by logging off the foreign host,
or by typing ``quit'' or ``close'' while in local command mode.
.Bl -tag -width /usr/share/misc/termcap -compact
.It Pa /usr/share/misc/termcap
.It Pa /usr/share/misc/map3270
4994 style transparent mode command is invoked when
4994 style transparent output from the remote host.
Output and input pipes are created for communication between the two
The pipes are closed when a 3270 clear command is received from the remote
hosts, signalling the end of transparent mode output.
Transparent mode is necessary for sending
control characters over the
3270 terminal connection;
graphics terminal support is accomplished this
commands should note that the
stdin pipe end will be in
checks the following environment variables:
Information on these can be found in
.%T "Yale ASCII Terminal Communication"
.%B "System II Program Description/Operator's Manual"
Tn3270 is slow and uses system resources prodigiously.
Not all 3270 functions are supported,
nor all Yale enhancements.
Error conditions (attempting to enter data in a protected field, for
example) should cause a message to be sent to the user's terminal
instead of just ringing a bell.