From owner-freebsd-questions  Thu Sep 17 07:43:31 1998
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To: "Kevin Kyeong-il CHOI" <kevin.choi@cnes.fr>
cc: "FreeBSD Question" <freebsd-questions@FreeBSD.ORG>,
        "FreeBSD Net" <freebsd-net@FreeBSD.ORG>,
        tcp-over-satellite@achtung.sp.trw.com
Subject: Re: Why FreeBSD (or Solaris as well) get stuck in case of long delay ? 
In-reply-to: Your message of "Thu, 17 Sep 1998 08:59:32 +0200."
             <006801bde208$b8e51ac0$52099584@pc-kichoi.cst.cnes.fr> 
From: David Greenman <dg@root.com>
Reply-To: dg@root.com
Date: Thu, 17 Sep 1998 07:37:48 -0700
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>	Capacity = RTT x Bandwidth.
>and the capacity would be limited by the window size.
>
>Here, I used 64K for Window size (65536), so the Bandwidth
>should be
>	
>	Bandwidth = Capacity (65536) / RTT
>
>I made the delay in one way as 200 ms, and RTT becomes 400 ms, so
>the nominal Bandwidth becomes 1310720 bps = 1.3 Mbps.
>
>Curiously enough, between two Windows boxes, the maximum bandwidth
>is obtained, which is about 1.0 ~ 1.1 Mbps.
>
>BUT, for FreeBSD, or for Solaris, I obtain only 200 ~ 300 kbps.
>(precisely 200 kbps for Solaris, and 300 kbps for FreeBSD).

   FreeBSD is almost certainly still using a window of 16KB. There are
problems in the code related to changing the socket buffer size after the
system is up. You pretty much have to modify the default value in the
kernel source files in order to use a larger window.

-DG

David Greenman
Co-founder/Principal Architect, The FreeBSD Project

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