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SubjectRe: Slow PPP - caused by duplicate packets?
On Sat, 30 Mar 1996, Alan Cox wrote:

> > It _looks_ like the other end is ignoring our first ACK, so it times out,
> > and then sends the packet again. And then we ACK it twice (that's normal
> > linux behaviour - there's the "normal" ACK, and then there is an extra
> > one that comes from the fact that the linux TCP code decides we'd better
> > ack again when we got a packet re-sent).
> >
> > Now, WHY is Solaris ignoring our first ACK?
> Is our first ack falling out of the cable, or not being sent or
> something like that.
I have been listening to this thread for a while now. I'm running basically
the same setup with no slow-downs seen from 1.3.57 through 1.3.80, which
I am now running.
This sounds like a timing problem at the Solaris. I have seen this kind
of problem over sdlc links before, where one side was always off building
a buffer when the ack came, and missed it, causing an unnecessary retry
of the buffer send.
My suggestion isn't trivial to implement, but, if you can tweak the code
at your end to send out two acks the first time I suspect the problem
will go away.
BTW, did I hear that this is an external modem? It is possible that the
handshaking problem is with your own modem (ie. the modem doesn't sent
the ack because it never received it due to being busy on another task)
and not between you and the Solaris. Have you tried other hosts?

Thanks for your time,


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