As per Relevance of the word possible, we have this rfc below:
Network Working Group J.
Request for Comments: 855 J.
Obsoletes: NIC 18640 May 1983
TELNET OPTION
This RFC specifies a standard for the ARPA Internet community. Hosts
the ARPA Internet are expected to adopt and implement this standard
The intent of providing for options in the TELNET Protocol is to
hosts to obtain more elegant solutions to the problems of
between dissimilar devices than is possible within the
provided by the Network Virtual Terminal (NVT). It should be
for hosts to invent, test, or discard options at will. Nevertheless,
is envisioned that options which prove to be generally useful
eventually be supported by many hosts; therefore it is desirable
options should be carefully documented and well publicized.
addition, it is necessary to insure that a single option code is
used for several different options
This document specifies a method of option code assignment and
for documentation of options. The individual responsible for
of option codes may waive the requirement for complete documentation
some cases of experimentation, but in general documentation will
required prior to code assignment. Options will be publicized
publishing their documentation as RFCs; inventors of options may,
course, publicize them in other ways as well
Option codes will be assigned by
Jonathan B.
University of Southern
Information Sciences Institute (USC-ISI
4676 Admiralty
Marina Del Rey, California 90291
(213) 822-1511
Mailbox = POSTEL@USC-
Documentation of options should contain at least the following sections
Section 1 - Command Name and Option
Section 2 - Command
The meaning of each possible TELNET command relevant to
option should be described. Note that for complex options,
Postel & Reynolds [Page 1]
RFC 855 May 1983
"subnegotiation" is required, there may be a larger number
possible commands. The concept of "subnegotiation" is
in more detail below
Section 3 - Default
The default assumptions for hosts which do not implement, or use
the option must be described
Section 4 -
A detailed explanation of the motivation for inventing
particular option, or for choosing a particular form for
option, is extremely helpful to those who are not faced (or don'
realize that they are faced) by the problem that the option
designed to solve
Section 5 - Description (or Implementation Rules
Merely defining the command meanings and providing a statement
motivation are not always sufficient to insure that
implementations of an option will be able to communicate
Therefore, a more complete description should be furnished in
cases. This description might take the form of text, a
implementation, hints to implementers, etc
A Note on "Subnegotiation
Some options will require more information to be passed between
than a single option code. For example, any option which requires
parameter is such a case. The strategy to be used consists of
steps: first, both parties agree to "discuss" the parameter(s) and
second, the "discussion" takes place
The first step, agreeing to discuss the parameters, takes place
the normal manner; one party proposes use of the option by sending
DO (or WILL) followed by the option code, and the other party
by returning a WILL (or DO) followed by the option code. Once
parties have agreed to use the option, subnegotiation takes place
using the command SB, followed by the option code, followed by
parameter(s), followed by the command SE. Each party is presumed
be able to parse the parameter(s), since each has indicated that
option is supported (via the initial exchange of WILL and DO).
the other hand, the receiver may locate the end of a parameter
by searching for the SE command (i.e., the string IAC SE), even
the receiver is unable to parse the parameters. Of course,
party may refuse to pursue further subnegotiation at any time
sending a WON'T or DON'T to the other party
Postel & Reynolds [Page 2]
RFC 855 May 1983
Thus, for option "ABC", which requires subnegotiation, the formats
the TELNET commands are
IAC WILL
Offer to use option ABC (or favorable acknowledgment of
party's request
IAC DO
Request for other party to use option ABC (or
acknowledgment of other party's offer
IAC SB ABC <parameters> IAC
One step of subnegotiation, used by either party
Designers of options requiring "subnegotiation" must take great
to avoid unending loops in the subnegotiation process. For example
if each party can accept any value of a parameter, and both
suggest parameters with different values, then one is likely to
an infinite oscillation of "acknowledgments" (where each
believes it is only acknowledging the new proposals of the other).
Finally, if parameters in an option "subnegotiation" include a
with a value of 255, it is necessary to double this byte
accordance the general TELNET rules
Postel & Reynolds [Page 3]
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
RFC documents can be found at I.E.T.F.
Relevance System Copyright © 2002 Spectrum WorldResearch
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