Revised Telnet status option

　　Revised TelnetStatus Option

　　NIC 31154 (25 Oct. 74)

　　Request for Comments: 651

　　D. Crocker (UCLA-NMC) 25 Oct. 74

　　RFC# 651

　　Online file: <[ISI]STATUS-OPTION-REVISION.RNO

　　Revised Telnet Status Option

　　1. Command name and code

　　STATUS 5

　　2. Command meanings

　　As described in the NAOL and NAOP option specifications, this option applies to a simplex connection.

　　IAC DO STATUS

　　Sender of DO wishes to be able to send requests for status-of-options information, or confirms that he is willing to send such requests.

　　IAC WILL STATUS

　　Sender of WILL wishes or agrees to send status information, spontaneously or in response to future requests.

　　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.)

　　3. Default

　　DON'T STATUS/WON'T STATUS. That is, the current status of options will not be discussed.

　　4. Motivation for the option

　　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 could lead to the nonterminating request loop problem discussed in (NIC #16237). The changes to the option, described in this paper, allow STATUS to fit into the normal structure of Telnet options, by deferring the actual transfer of status information to the SB command. Additionally, the numbers of bytes that must be sent to describe the state of the options has been considerably reduced.

　　5. Description of the option

　　WILL/DO are now 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.

　　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

　　WILL RCTE

　　SB RCTE <11><1><24> SE

　　DO NAOL

　　SB NAOL DS <66> SE

　　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;it will send instruction for controlling the other side's terminal printer; it will discuss the line width for data it is sending.