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Date:      Thu, 10 Mar 2005 21:52:50 -0800
From:      Luigi Rizzo <rizzo@icir.org>
To:        jim song <jingmin.song@gmail.com>
Cc:        freebsd-ipfw@freebsd.org
Subject:   Re: why my dummynet queue not work?
Message-ID:  <20050310215250.A65126@xorpc.icir.org>
In-Reply-To: <d018391a050310213469df3025@mail.gmail.com>; from jingmin.song@gmail.com on Fri, Mar 11, 2005 at 01:34:10PM +0800
References:  <d018391a050310200327a01c48@mail.gmail.com> <20050311043933.GA28686@odin.ac.hmc.edu> <d018391a050310213469df3025@mail.gmail.com>

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On Fri, Mar 11, 2005 at 01:34:10PM +0800, jim song wrote:
> Brooks,
> 
> Actually I use the freebsd box as an router. I set the tcp window in 
> another two windows box running iperf (iperf -w 5M).
> 
> Before I add in the pipes, the throughputs could reach 300M, but after
> I config in the two pipes(200M bandwidth, 25ms delay), the throughput
> degrade to about 5M. 

but the bandwidth is at most 1 window/RTT, where the window is
min(sockbuf_size, TCP_window). With your pipe setting
you have 50-100ms RTT, so the above would suggest that your
effective window is around 500kbit or roughly 64KBytes.
all consistent with an improper window setting

luigi

> BTW, is there some limitations to tcp connections passing through a 
> router?
> 
> Thanks,
> --Jingmin
> 
> On Thu, 10 Mar 2005 20:39:33 -0800, Brooks Davis
> <brooks@one-eyed-alien.net> wrote:
> > 
> > Why are you using the queue parameter at all?  If you just want to
> > emulate a pipe there is usually no need to do that.  Have you adjusted
> > your socket buffers in addition to your max TCP window size?
> > 
> > -- Brooks
> >
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