ppg@oasis.icl.co.uk (Philippe Goujard) (05/08/91)
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@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@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@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@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@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@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@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@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@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@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@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@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@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. -- --------------------------------------------------------------------------- Philippe GOUJARD Email : ppg@oasis.icl.co.uk "Another version of MS/DOS is called OS/2" : ICL News ---------------------------------------------------------------------------