From: David Miller <davem@davemloft.net>
To: dccp@vger.kernel.org
Subject: Re: Sensitivity of TFRC throughput equation wrt to changes of RTT
Date: Fri, 13 Apr 2007 19:33:56 +0000 [thread overview]
Message-ID: <20070413.123356.21601263.davem@davemloft.net> (raw)
In-Reply-To: <200704131303.03072@strip-the-willow>
From: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Date: Fri, 13 Apr 2007 13:03:02 +0100
> RFC 3448 gives in section 8 the following alternative format
> of the throughput equation (which is directly responsible for
> the alllowed sending rate X):
>
> s
> X = --------
> R * f(p)
>
> This shows that the dependence is reciprocal. Thus using an RTT
> which differs by a factor of 10 to account for in-stack processing
> results an a throughput reduction of factor 10.
>
> In other words, 90 Mbits/sec becomes 9 Mbits/sec.
What I'd like to know in all this is why the RTT influences the
sending rate at all in such a manner. Please teach me :)
If I have a 10gbit pipe all the way to the planet mars I should
still be feeding that pipe at a rate of 10gbit. :)
TCP doesn't have any of these problems, and we use incredibly coarse
timestamping for RTTs. We get jiffies granularity at best, with many
in-stack delays, and we still send at full line rate over large RTTs.
next prev parent reply other threads:[~2007-04-13 19:33 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-04-13 12:03 Sensitivity of TFRC throughput equation wrt to changes of RTT Gerrit Renker
2007-04-13 19:33 ` David Miller [this message]
2007-04-13 19:52 ` Ian McDonald
2007-04-13 20:27 ` Gerrit Renker
2007-04-13 20:43 ` David Miller
2007-04-13 20:54 ` David Miller
2007-04-14 5:43 ` Eddie Kohler
2007-04-15 16:15 ` Gerrit Renker
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