
PC/telnet, Version 7.1

A remote login package for the IBM PC, using the TCP/IP protocol
and emulating a display terminal.


Usage:

     telnet hostname
or
     telnet -p portno hostname

Where "hostname" is either a character-string name of the target
host, or an internet address in standard form.  (See the section
on hostnames in the network overview for more details.)  When
used with the "-p" option, the argument "portno" is used as a
port number at the target machine.  This feature is used to
connect with certain telnet-like services available on some
hosts.

From the point of view of the target host, PC/telnet emulates a
standard "network virtual terminal".  From the point of view of
the keyboard user, PC/telnet emulates a Heath H19 terminal.
The terminal emulation is only approximate.  A set of conventions
and list of incompatibilities appears on the next page.

Typing the command with the name or internet address of a target
host causes PC/telnet to try to establish a connection.  When 
that connection is successful, the target host should display 
its greeting banner.  The following conventions apply to the 
translation between H19 emulation and network virtual terminal 
emulation:

   1)  Function key F10 is an escape used to invoke PC/telnet
       functions.  F10 followed by a question mark displays a list
       of escape sequences.  Others are F10 followed by:
         a     Send "Are You There?" inquiry to the target host.
         b     Send "break" to the target host.
         c     Close the connection and exit from telnet.
         e     Send to target on every typed character.
         l     Local echo.  (PC/telnet echos typed input.)
         E     Send to target only when End-Of-Line is typed.
         q     exit from telnet without closing connection.
         r     Remote echo.  (Target host echos typed input.)
         x     Send any outstanding data now.
         U     turn on the line-25 clock and status report
               (default is on)
         u     turn off the line-25 clock and status report.

   2)  Function key F10 is also used to change the mode of operation 
       of the terminal emulator within PC/telnet.  These escapes are:
         B     Backspace key sends BS, control-backspace sends DEL.
         D     Backspace key sends DEL, control-backspace sends BS.
         d     If output line too long, discard extra characters.
         w     If output line too long, wrap around to next line.

   3)  The PC "Print-Screen" feature, triggered by key "PrtSc",
       can be used from within PC/telnet, but immediately preceding
       its use one must restore the display buffer to the format
       expected by PrtSc.  Function key F10 typed twice does this
       format adjustment.

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Closing connections:

At the end of a login session, some hosts will close the 
connection, in which case PC/telnet exits, returning to the 
PC operating system.  Other hosts issue an invitation for 
another login.  In the latter case, type F10 followed by "c" 
to close the connection and exit from PC/telnet.  Other methods 
of exiting, such as F10 followed by "q", or powering down the PC, 
will leave a dangling TCP/telnet connection that some hosts may 
not clean up properly.  A later attempt to login to that host 
from the same PC may encounter interference from the unclosed 
previous connection.

If you close a connection without logging out, most hosts will
deal with the situation in the same way they handle telephone
line hangups.  If you exit telnet without either logging out or
closing the connection, the host may not realize you are gone,
and there is no way to pick up the connection again.  (The host,
noticing lack of activity for a long time, may eventually log 
you out and close the connection.)

If you try to open a connection to a host that does not respond,
PC/telnet will try eight times, then display an error message 
and exit.  Note that this message may mean either that the 
target host is not listening to the network or that some network 
or gateway in the communication path to that host has failed.  
(The command PC/ping  may be useful in isolating the trouble.)

Versions of PC/telnet are available for the Ethernet and for 
serial lines.  On a serial line, at speeds below 9600 baud, 
the combination of remote echo and send-on-every-character 
modes causes display to fall far behind typed input.  Local 
echo and send-on-newline modes are recommended for operation 
at lower line speeds.


Terminal emulation conventions and compatibility:

The following conventions allow the PC keyboard to behave like
that of a Heath H19:

1)  There is no repeat key.  To repeat any key, hold it down.
2)  The function keys are keys F1-F5.
3)  The color keys are F6(blue), F7(red) and F8(gray).
4)  The H19 has separate keys for ASCII "Carriage Return" and
    ASCII "Line Feed".  These two functions are combined on 
    the PC "Enter" key (the one to the right of the tilde key).  
    To send an ASCII CR, type "enter".  To send an ASCII LF, 
    type "control-enter".
5)  The H19 has separate keys for ASCII "Backspace" and ASCII
    "Delete".  These two functions are combined on the PC 
    "back-space" key (the one to the right of the equal-sign 
    key).  To send ASCII DEL, type "backspace".  To send ASCII 
    BS, type "control-backspace".  A customization option and 
    an F10 escape allow interchanging backspace and control-
    backspace.  For convenience, the keypad key labeled "Del" 
    also sends an ASCII DEL.
6)  The PrtSc key operates normally on the PC.  That is, it
    sends the current display to an attached printer.


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7)  Note that the emulator exactly emulates the Heath H19 line
    wraparound feature.  That is, in line wraparound mode, the
    emulator automatically goes to the next line after placing
    a character in column 80, rather than waiting to see if the
    program or typist will try to put something in column 81.

Heath H19 features not emulated:
          hold screen/scroll         keyclick disable
          graphics                   keyboard disable
          shifted keypad             block cursor
          alternate keypad           AutoCR
          identify as VT-52          AutoLF
          transmit page              transmit 25th line
          offline/online switch      parity enable
          XOFF/XON flow control      most ANSI escapes
          control-suppression of transmitting display mgt codes
          restore power-up configuration
          ESC x setting of parameters
          control-space does not send null (but control-2 does)


File transfer with PC/telnet

The PC/tftp server package can be invoked while using PC/telnet.
With this feature, one can use PC/telnet to log in to a remote
host, and then move files between that host and the PC, using the
other host's tftp command to control the transfer.  Compared with
initiating the transfer from the PC, this method has two 
advantages:

   1)  Because the user authenticates himself upon logging in 
       to the distant host he can transfer any files to which 
       he has access, not just publicly accessible files.

   2)  The user can invoke other commands on the distant host
       in conjunction with the transfer.  (E.g., compile and
       load a program before sending it.)

Seven functions of PC/telnet support tftp service.  They are
invoked by typing function key F10 followed by:

   T    Enable the tftp server.

   t    Disable the tftp server (upon completion of any
        transfer currently in progress).

   i    Send this PC's internet address, in decimal format, as 
        if it had been typed on the keyboard.  Control-i sends 
        the address in octal format.  This function simplifies
        the issuing of tftp commands on other systems.

   I    Display this PC's internet address on line 25 in octal 
        and decimal formats.  (For use if the other system needs 
        this address in some odd format.)

   y    Accept a file transfer request.

   n    Refuse a file transfer request.

   A    Accept all file transfer requests, without asking.

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When another host requests a file transfer to or from this PC,
the PC/tftp server asks the PC/telnet user for permission to
accept the request. (Type F10/y or F10/n.)  For a successful
transfer, the user must accept the request before the remote 
host loses patience, times out, and aborts the transfer.  
Hosts commonly have a 10 to 30 second timeout.

Further information on file transfer may be found in the
description of PC/tftp service, and in the description of tftp
usage for the remote host.  Some hosts have a tftp command 
that is similar to the PC/tftp command, so that writeup in 
this manual may offer some help if no other documentation is 
available.


Experimental feature:

The PC/telnet escape F10/! invokes a nested DOS command 
interpreter, permitting the user to invoke other DOS commands
locally on the PC without shutting down the telnet connection.
This feature has been added quite recently, and has not been
fully checked out; user-friendliness and freedom from surprises,
restrictions, and bugs is not guaranteed.  The feature requires 
a configuration of 192K bytes of memory, and while running the
nested command interpreter, network commands cannot be used. 
One should not stay in DOS for extended periods because while in
DOS, arriving messages are ignored, and if the host at the other 
end of the telnet tries to send such a message it may become 
impatient with the lack of response from the PC, and close the 
connection.  To return to PC/telnet, issue the DOS command EXIT.


Customization:

The following parameters of telnet can be customized with the
PC/custom command:

   1)  The parameters for TCP window size and TCP low window
       are of particular interest to PC/telnet users.  See 
       the description of PC/custom for explanation of these
       parameters.

   2)  Start in line-at-a-time mode or character-at-a-time mode.


DOS note:

The DOS feature of redirecting output to a file cannot be used
for PC/telnet display output.

Debugging note:

There are several debugging features built in to PC/telnet that 
can be useful in tracing network problems.  See the section 
"debugging options" for more information.


21 January 1985.  This document is in file telnet.txt
