Subject: Re: TCP socket buffers automatic sizing
To: Blair Sadewitz <>
From: Steven M. Bellovin <>
List: tech-net
Date: 07/21/2007 20:57:22
On Sat, 21 Jul 2007 20:29:17 -0400
"Blair Sadewitz" <> wrote:

> I should note that, as Steve Bellovin reported, I've gotten roughly
> the same performance improvement simply by increasing the socket
> buffer size.  Of course, this can be a waste, but waste is always
> relative to reward. ;)
> As I said before, I haven't tested this systematically, but with
> ftp/http transfers, it seems that I don't notice much benefit until I
> hit around 1MiB/s.  At ~2MiB/s, downloads from a site nearby seem to
> run on average about 25% faster.
A lot depends on file size and path latency.  TCP ramps up slowly, and
not many http files are big enough for the difference to matter much.
The bigger buffer matters a lot more for high-delay paths.  (My office
is only 8 ms from my house; my primary Internet server is only 6 ms from
my office.  But my secondary server is ~40 ms from my primary server.)

		--Steve Bellovin,