4.3 BSD out-of-band handling

[Chris Torek]

In article <464 at tandem.Tandem.com> rfox at tandem.Tandem.com (Richard Fox) writes:
>I have been looking at how 4.3 handles out-of-band data.

This is actually an interesting problem.

First, TCP does not *have* out of band data; it has `urgent' data.
According to RFC961, the urgent pointer is supposed to point to the
first octet past the urgent data; 4.3BSD makes it point to the last
(normally only) octet of urgent data.  If sending into a zero window,
the code forces the urgent byte to be sent (via tp->t_force) but
thinks it is doing a persist probe.  Everything is much confused.

XNS *does* have out of band data.  Out of band data may be sent at
any time, but is limited to one byte.  This mostly works in 4.3BSD,
since the protocol matches the software fairly closely.  (There are
still problems with multiple outstanding out of band bytes, although
XSIS whatever-its-number-is might outlaw this.)

The socket code is sprinkled with comments to the effect that the
current OOB code should be thrown out, but Mike has not yet come up
with a good replacement.

If you have a favourite implementation, you can send it to Berkeley
and see if they will take it.

(Incidentally, please do not put your own name in followup-to header
lines.  This merely confuses the news softare.  `Followup-to: author'
will send followups as replies in some news software, but not all.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris at mimsy.umd.edu	Path:	uunet!mimsy!chris