[95989] in North American Network Operators' Group
Re: Thoughts on increasing MTUs on the internet
daemon@ATHENA.MIT.EDU (Joe Loiacono)
Thu Apr 12 17:41:17 2007
In-Reply-To: <Pine.LNX.4.64.0704122245360.28703@uplift.swm.pp.se>
To: Mikael Abrahamsson <swmike@swm.pp.se>
Cc: NANOG list <nanog@merit.edu>, owner-nanog@merit.edu
From: Joe Loiacono <jloiacon@csc.com>
Date: Thu, 12 Apr 2007 17:31:01 -0400
Errors-To: owner-nanog@merit.edu
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I believe the formula applies when the TCP window size is held constant
(and maybe as large as is necessary for the bandwidth-delay product).
Obviously P going to zero is a problem; there are practical limitations.
But bit error rate is usually not zero over long distances.
The formula is not mine, it's not new, and there is empirical evidence to
support it. Check out the links for more (and better :-) info.
Joe
owner-nanog@merit.edu wrote on 04/12/2007 04:48:09 PM:
>
> On Thu, 12 Apr 2007, Joe Loiacono wrote:
>
> > Window size is of course critical, but it turns out that MTU also
impacts
> > rates (as much as 33%, see below):
> >
> > MSS 0.7
> > Rate = ----- * -------
> > RTT (P)**0.5
> >
> > MSS = Maximum Segment Size
> > RTT = Round Trip Time
> > P = packet loss
>
> So am I to understand that with 0 packetloss I get infinite rate? And
TCP
> window size doesn't affect the rate?
>
> I am quite confused by this statement. Yes, under congestion larger MSS
is
> better, but without congestion I don't see where it would differ apart
> from the interrupt load I mentioned earlier?
>
> --
> Mikael Abrahamsson email: swmike@swm.pp.se
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<br><font size=2><tt>I believe the formula applies when the TCP window
size is held constant (and maybe as large as is necessary for the bandwidth-delay
product). Obviously P going to zero is a problem; there are practical limitations.
But bit error rate is usually not zero over long distances. </tt></font>
<br>
<br><font size=2><tt>The formula is not mine, it's not new, and there is
empirical evidence to support it. Check out the links for more (and better
:-) info.</tt></font>
<br>
<br><font size=2><tt>Joe</tt></font>
<br>
<br><font size=2><tt>owner-nanog@merit.edu wrote on 04/12/2007 04:48:09
PM:<br>
<br>
> <br>
> On Thu, 12 Apr 2007, Joe Loiacono wrote:<br>
> <br>
> > Window size is of course critical, but it turns out that MTU
also impacts<br>
> > rates (as much as 33%, see below):<br>
> ><br>
> > MSS 0.7<br>
> > Rate = ----- * -------<br>
> > RTT (P)**0.5<br>
> ><br>
> > MSS = Maximum Segment Size<br>
> > RTT = Round Trip Time<br>
> > P = packet loss<br>
> <br>
> So am I to understand that with 0 packetloss I get infinite rate?
And TCP <br>
> window size doesn't affect the rate?<br>
> <br>
> I am quite confused by this statement. Yes, under congestion larger
MSS is <br>
> better, but without congestion I don't see where it would differ apart
<br>
> from the interrupt load I mentioned earlier?<br>
> <br>
> -- <br>
> Mikael Abrahamsson email: swmike@swm.pp.se<br>
</tt></font>
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