RFC 859 - Telnet Status Option
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. 1. Command Name and Code STATUS 5 2. Command Meanings 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.) 3. Default DON'T STATUS, WON'T STATUS 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 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. 5. Description of the Option 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. 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.