RFC 651 (rfc651) - Page 1 of 1

Revised Telnet status option

Revised Telnet Status Option
NIC 31154 (25 Oct. 74)
Request for Comments: 651
D. Crocker (UCLA-NMC) 25 Oct. 74
RFC# 651
Online file: 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  SE
         DO NAOL
         SB NAOL DS  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.