Telnet, Rlogin, and Terminal Servers

Keith Mitchell (mcvax!!keith@uunet.UU.NET)
Tue, 1 Nov 88 13:20:14 GMT

>From the correspondence on this subject, people appear to prefer the average
Rlogin implementation over the average Telnet one because:

1) It passes terminal type
2) It bypasses the need for username/password to be entered
3) No newline etc processing is applied to data transferred
4) It has better out-of-band data handling
5) It has better flow-control handling
6) It has window-size negotiation

A full (as opposed to average) Telnet implementation can provide (1), (3),
(4), and (6), and the Telnet standard is sufficently general that extensions
to cover (2) and (5) are certainly possible. I still feel Telnet is the
protocol to go with - networking is about connecting heterogenous systems,
not just Unix ones, and achieving the goal of universal connectivity/
interoperability is never going to be accomplished with non-documented

The problem is that although Telnet defines a general functionality, most
implementations only provide a subset of this. Rlogin implements a
different subset of this functionality (It has no definition distinct
from the implementation). What is really wanted is an
implementation which provides a more general union of both these subsets.

I think the approach implementors should take therefore, is to provide both
Rlogin and Telnet, but concentrate on extending Telnet so it can meet all
peoples' needs. We need both in the meantime, not least because the whole
situation is very much "horses for courses". (The Telnet vs Rlogin arguments
strike me as very similar to those for NFS vs RFS.)

The discussion on this subject has been very useful, and I will make
sure it is input to the next phase of SpiderPort development.

Keith Mitchell

Spider Systems Ltd. Spider Systems Inc.
65 Bonnington Road 12 New England Executive Park
Edinburgh, Scotland Burlington, MA 01803
+44 31-554 9424 +1 (617) 270-3510 ...!uunet!ukc!spider!keith

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