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.)
Hedrick