Summary : What is the use of Telnet ?

[Philippe Goujard]

This is a summary of the question posted on comp.unix.questions on
"What is the use of Telnet?"

The original message was :

=======================
I'm currently developping a version of the ISO Virtual Terminal and I'm
in charge of the Asynchronous mode and Telnet emulation.

I have a good theorical knowledge of telnet (RFC854) and I can use telnet
with our unix machines over TCP/IP. But for me it works more or less like
rlogin. Therefore I cannot realy figure what is telnet used for (or was used
as the rfc is from 1983). 

What do you use telnet for? (and why not "only" rlogin?)
Do you use the "transmit binary" facility? If yes for what purpose?
(transfering files, driving directly the screen?, ...)
Do you use facilities like "Are You There" or "Abort Output" or "Transmit
Go Ahead"?
======================

I received 15 messages that answer the following points :

1) Telnet vs Rlogin
===================

Most of the people agree that Telnet was invented before rlogin and is more
a standard specially amongst non-unix machines. (somebody mentioned a version
of rlogin for vax/vms but is not sure).

==
From: Neil Rickert <rickert at cs.niu.edu>

  telnet is a widespread protocol with an internet standard.  rlogin was
designed for unix system on a LAN, although in practice its use has
spread beyond that.

==
From: "Charles H. Buchholtz" <chip at pender.ee.upenn.edu>

I use telnet to reach machines that do not support rlogin, or when a
machine temporarily cannot be reached via rlogin.  When an rlogin
fails, the first thing I do is to try telnet.  This helps me determine
whether its an rlogin problem or an inetd problem.  (next comes ping,
etc).

The official rule of thumb around here is, "rlogin to unix machines,
telnet to non-unix machines."

==
From: ekrell at ulysses.att.com

rlogin is Unix-specific while telnet has been ported to non-Unix
machines. rlogin uses select() so that you can do it all in one
process. telnet needs to fork() into 2 processes: one reading
and one writing.

==
From: "Jonathan I. Kamens" <jik at pit-manager.mit.edu>

  The main difference between telnet and rlogin is that telnet was designed to
be a general purpose, extensible protocol that could be augmented and enhanced
as it became necessary to do so, while rlogin/rsh/rcmd was designed as a quick
hack to allow remote access to other Unix boxes under BSD.

(Jonathan also wrote a good article in comp.unix.questions about the history
of telnet vs rlogin)

==
From: Frank Peters <fwp1 at ra.msstate.edu>

Because telnet came first and many non-unix systems don't support rlogin.

Once upon a time telnet was THE remote terminal protocol.  But it didn't
pass UNIX environment information and required a user to deal with the
entire login process for each telnet.

So the berkeley people developed the r commands (rlogin, rsh and the like)
to get around this limitation.  But much of that was UNIX specific and
not at all applicable to non-UNIX operating systems.  So many didn't 
implement it.  

Now most of the good things in rlogin are included in telnet.

==
From: dik at cwi.nl

When I try to rlogin to the Data General sitting next to the other machines
that runs AOS/VS it will not understand me.  Rlogin contains a larger protocol
than telnet and is valid only for Unix machines (and some systems that have
particularly learned to understand it).  Telnet works to all systems that
implement TCP/IP.

==
From: Eric S Hvozda <hvozda at endor.cs.psu.edu>

I use it for going to VAXens and VM/SPs from my UNIX box.  rlogin is not
available from UNIX to these machines at my site...

==
From: Doug Burks <dbx at olympic.atmos.colostate.edu>

     I can only answer your questions for 'telnet'. I use 'telnet' to log
into a VMS machine from an MS-DOS machine, log into a Unix machine from
an MS-DOS machine, as well as logging into a Unix machine from a Unix
machine.  Get the picture?  Not all of the world is Unix.


2) The telnet options 
=====================

Here the answers are more vague. No one seems to use them (apparently because
there are more powerfull tools such as FTP). At least some persones use AYT
or AO but only from time to time. 

Unfortunately (for me) it doesn't help me a lot for I mostly wanted to know
the use of the "transmit binary" option, if it was used to transfer a file
or to drive directly the screen. (And what happends to characters lower than
32 or greater than 127? are they displayed or mapped into something more
printable? If not should they be?). 


==
From: Frank Peters <fwp1 at ra.msstate.edu>

>Do you use the "transmit binary" facility? If yes for what purpose?
>(transfering files, driving directly the screen?, ...)

A program, tn3270, for talking to IBM mainframes, uses telnet binary
protocol as its basis.  (BTW, IBMs are one of those boxes that don't
support rlogin).

>Do you use facilities like "Are You There" or "Abort Output" or "Transmit
>Go Ahead"?

Yes.  AYT is useful when things seem to hang and you want to try to determine
whether the link has died.

AO is useful for links that have a slow component.  For instance, a 1200
baud modem connection to a terminal server that then goes to a host across
the internet.  The host will see a full speed internet link, not a 1200
baud link.

==
From: Noam Mendelson <c60b-1eq at web.berkeley.edu>

>Do you use the "transmit binary" facility? If yes for what purpose?
>(transfering files, driving directly the screen?, ...)
>Do you use facilities like "Are You There" or "Abort Output" or "Transmit
>Go Ahead"?

I rarely use any of those odd features of telnet; perhaps send an
AYT if I think the remote system is hung.

==
From: " Achille Hui, the Day Dreamer " <eillihca at embezzle.stanford.edu>

ppg> Do you use the "transmit binary" facility? If yes for what purpose?

Never, ftp do a much better job.
I doubt anybody use them at all.

==
From: Martin Boyer <gamin at ireq-robot.hydro.qc.ca>

>Do you use the "transmit binary" facility? If yes for what purpose?
>(transfering files, driving directly the screen?, ...)

Actually, just yesterday I needed something to transfer files from an
account which didn't have ftp set up properly.  Unfortunately our
telnet doesn't have anything that looks like a "transmit binary"
facility.

==
From: mbm at dsbc.icl.co.uk (Malcolm Mladenovic)

The main difference between the two is that rlogin is intended for use
when both systems are unix-like systems, telnet is simple enough so that
it can be used to almost anything.  Rlogin only connects to a paticular
'rlogin' service on the remote host, telnet can be used to talk to any
(text-based) service, for example telnet <system> 25 will connect you
directly to the smtp daemon on the remote system, which you can then talk
to as if you were a mail agent such as sendmail.



-- 
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Philippe GOUJARD                                Email : ppg at oasis.icl.co.uk
"Another version of MS/DOS is called OS/2" : ICL News
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