[sclug] Exporting a terminal over the network

[Roland Turner SCLUG]

John Stumbles wrote:


> Roland Turner (SCLUG) wrote:
>>
>> Are you certain? The man page claims a complete set of TERMIOS options
>> including xon and xoff (which, despite the ridiculous names, relate to
>> inward and outward flow control characters respectively).
>
> IIRC (long time since I plumbed layer 0 :)) Xoff & Xon (sometimes
> generated from the keyboard by ^S and ^Q) tell the other end of the
> link  to stop & restart (respectively) transmission. Inward & outward
> flow  control is acheived by sending Xoff & Xon chars in each
> direction: the  characters used are the same in each direction. (You
> could also have  Xoff/Xon aka software flow control in one direction
> and hardware, or no,  flow control in the other: the two directions of
> data flow are
> effectively independent channels.)


I'm not clear whether you are adding to or contradicting my comments (I
don't think that the original poster was actually asking to have XON/XOFF
flow control explained to him). To clarify my own:

- According to the stty manpage, the 'ixon' option enables/disables
inbound flow control (that is, it enables/disables the recognition of
inbound XON/XOFF characters to control the flow of the outbound character
stream).

- According to the stty manpage, the 'ixoff' option enables/disables
outbound flow control (that is, it enables/disables the sending of
XON/XOFF characters to attempt to control the remote sender of the inbound
character stream).

- The names of the options are clearly misleading, 'ixonxoff' and
'oxonxoff'  would have been better choices but, like umount, they have the
weight of history behind them.

- According to the socat manpage, the TERMIOS option set includes both
ixon and ixoff, which suggests that socat is expected to be capable of
enabling XON/XOFF flow control in both directions.

I've not actually tested this; inband flow control is the work of the
devil and I avoid it like the plague. However, when faced with a 3-wire
configuration, typical in embedded applications, little else is available
and my commisserations on the need to rely on this are offered to the
original poster.

- Raz