RFC 1080 (rfc1080) - Page 3 of 4

Telnet remote flow control option

Alternative Format: Original Text Document


RFC 1080           Telnet Remote Flow Control Option       December 1988


      DON'T TOGGLE-FLOW-CONTROL

         Flow control information will not be exchanged.

4. Description of the Option

   Use of the option requires two phases.  In the first phase, the
   telnet processes agree that one of them will TOGGLE-FLOW-CONTROL.
   WILL and DO are used only in this first phase.  In general there will
   be only one exchange of WILL and DO for a session.  Subnegotiations
   must not be issued until DO and WILL have been exchanged.  It is
   permissible for either side to turn off the option by sending a WONT
   or DONT.  Should this happen, no more subnegotiations may be sent,
   unless the option is reenabled by another exchange of DO and WILL.

   Once the hosts have exchanged a WILL and a DO, the sender of the DO
   TOGGLE-FLOW-CONTROL is free to send subnegotiations to enable and
   disable flow control in the other process.  Normally, the sender of
   the DO will be a host, and the other end will be a user telnet
   process, which is connected to a terminal.  Thus the protocol is
   normally asymmetric.  However it may be used in both directions
   without confusion should need for this arise.

   As soon as the DO and WILL have been exchanged, the sender of the
   WILL must enable flow control.  This allows flow control to begin in
   a known state.  Should the option be disabled by exchange of DONT and
   WONT, flow control may revert to an implementation-defined default
   state.  It is not safe to assume that flow control will remain in the
   state requested by the most recent subnegotiation.

   Currently, only two command codes are defined for the
   subnegotiations: flow control off (code 0) and flow control on (code
   1).  Neither of these codes requires any additional data.  However it
   is possible that additional commands may be added.  Thus
   subnegotiations having command codes other than 0 and 1 should be
   ignored.

      Here is an example of use of this option:

         Host1: IAC DO TOGGLE-FLOW-CONTROL

         Host2: IAC WILL TOGGLE-FLOW-CONTROL

         (Host1 is now free to send commands to change flow control.
         Note that host2 must now have enabled flow control.)






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