Network Working Group J. Postel
Request for Comments: 859 J. Reynolds
ISI
Obsoletes: RFC 651 (NIC 31154) May 1983
TELNET STATUS OPTION
This RFC specifies a standard for the ARPA Internet community. Hosts on
the ARPA Internet are expected to adopt and implement this standard.
This option applies separately to each direction of data flow.
IAC DON'T STATUS
Sender refuses to carry on any further discussion of the current
status of options.
IAC WON'T STATUS
Sender refuses to carry on any further discussion of the current
status of options.
IAC SB STATUS SEND IAC SE
Sender requests receiver to transmit his (the receiver's)
perception of the current status of Telnet options. The code for
SEND is 1. (See below.)
IAC SB STATUS IS ... IAC SE
Sender is stating his perception of the current status of Telnet
options. The code for IS is 0. (See below.)
This option allows a user/process to verify the current status of
TELNET options (e.g., echoing) as viewed by the person/process on the
other end of the TELNET connection. Simply renegotiating options
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RFC 859 May 1983
could lead to the nonterminating request loop problem discussed in
the General Consideration section of the TELNET Specification. This
option fits into the normal structure of TELNET options by deferring
the actual transfer of status information to the SB command.
WILL and DO are used only to obtain and grant permission for future
discussion. The actual exchange of status information occurs within
option subcommands (IAC SB STATUS...).
Once the two hosts have exchanged a WILL and a DO, the sender of the
WILL STATUS is free to transmit status information, spontaneously or
in response to a request from the sender of the DO. At worst, this
may lead to transmitting the information twice. Only the sender of
the DO may send requests (IAC SB STATUS SEND IAC SE) and only the
sender of the WILL may transmit actual status information (within an
IAC SB STATUS IS ... IAC SE command).
IS has the subcommands WILL, DO and SB. They are used EXACTLY as used
during the actual negotiation of TELNET options, except that SB is
terminated with SE, rather than IAC SE. Transmission of SE, as a
regular data byte, is accomplished by doubling the byte (SE SE).
Options that are not explicitly described are assumed to be in their
default states. A single IAC SB STATUS IS ... IAC SE describes the
condition of ALL options.
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RFC 859 May 1983
The following is an example of use of the option:
Host1: IAC DO STATUS
Host2: IAC WILL STATUS
(Host2 is now free to send status information at any time.
Solicitations from Host1 are NOT necessary. This should not
produce any dangerous race conditions. At worst, two IS's will
be sent.)
Host1 (perhaps): IAC SB STATUS SEND IAC SE
Host2 (the following stream is broken into multiple lines only for
readability. No carriage returns are implied.):
IAC SB STATUS IS
WILL ECHO
DO SUPPRESS-GO-AHEAD
WILL STATUS
DO STATUS
IAC SE
Explanation of Host2's perceptions: It is responsible for echoing
back the data characters it receives over the TELNET connection;
it will not send Go-Ahead signals; it will both issue and request
Status information.
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