Re: W/RTT verification, linux tcp buffers behaviour

[Constantinos Makassikis]

On 5/15/06, John Heffner <jheffner@xxxxxxx> wrote:
> Constantinos Makassikis wrote:
> > As it can be seen, we hardly reach 70 % of the value predicted by the
> > formula
> > and apparently it seems that it is due to the fact that MAX SND
> > remains relatively
> > low compared to SNDBUF.
>
> This is due to the fact that (differently than BSD) Linux treats socket
> buffer sizes as limits on the amount of kernel memory that socket
> buffers can consume, rather than the number of in-band TCP data they can
> hold.  There's a certain amount of overhead involved in storing the
> buffered data, so you'll see a correspondingly smaller window size, if
> the TCP window is limited by the socket buffer size.
>
>    -John

Thanks for pointing this significant conceptual difference.

Is there a way to predict the amount of overhead or the in-band TCP
data that can be hold ?
I believe that the reason the W/RTT formula is verified so poorly lies
in the fact I don't have
a good estimation of W.

Constantinos
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