[142491] in North American Network Operators' Group
Re: [pfSense Support] Strange TCP connection behavior 2.0 RC2 (+3)
daemon@ATHENA.MIT.EDU (Andreas Ott)
Tue Jun 28 11:24:48 2011
Date: Tue, 28 Jun 2011 08:23:46 -0700
From: Andreas Ott <andreas@naund.org>
To: Eugen Leitl <eugen@leitl.org>, williamejsalt@googlemail.com
In-Reply-To: <20110628085255.GX26837@leitl.org>;
from eugen@leitl.org on Tue, Jun 28, 2011 at 10:52:55AM +0200
Cc: NANOG list <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
Hi,
On Tue, Jun 28, 2011 at 10:52:55AM +0200, Eugen Leitl wrote:
> ----- Forwarded message from William Salt <williamejsalt@googlemail.com> -----
> From: William Salt <williamejsalt@googlemail.com>
> Date: Tue, 28 Jun 2011 08:03:25 +0100
> To: support@pfsense.com
> Subject: [pfSense Support] Strange TCP connection behavior 2.0 RC2 (+3)
> Reply-To: support@pfsense.com
> Each TCP connection starts very slowly, and will max out at around 190mbps,
> taking nearly 2 minutes to climb to this speed before *plateauing*.
>
> We have to initiate many (5+) connections to saturate the link with tcp
> connections with iperf.
> ----- End forwarded message -----
You pretty much solved your own puzzle right there: the throughput on a
single TCP connection will max out at the value determined by the bandwidth
delay product (excluding other strange conditions, such as deep buffers).
Here is a calculator online:
http://www.switch.ch/network/tools/tcp_throughput/
-andreas
[who has to explain this about once a week to customers who think
that they bought a GigE connection but then can't "ftp" a file from
coast to coast at 1Gbps throughput. Use multiple TCP streams!]
