Re: TCP (and SCTP) sucks on high speed networks

[David Borman <dab@BSDI.COM>]

> From: "Steven M. Bellovin" <smb@research.att.com>
> To: Matt Wakeley <matt_wakeley@agilent.com>
> Subject: Re: TCP (and SCTP) sucks on high speed networks 
> Date: Fri, 01 Dec 2000 17:14:05 -0500
...
> We, as a profession, don't know how to do better today, in the sense that 
> we don't have a solution that is (a) rationally deployable, (b) solves this 
> problem, (c) is "TCP-friendly", in the sense that it doesn't have undue 
> negative impact on existing RFC-compliant TCP streams, and (d) is 
> reasonably compliant with the Internet and the Internet philosophy.

I'm not sure that I agree with that.  It occurs to me that what is
really at issue here is a question of how much the congestion window
should be increased each RTT during CW avoidance.  Or more specifically,
the current algorithm (1 MSS) works well when the ratio between the
delay-bandwidth (DBW) and the MSS is small, but as DBW gets larger, and
the ratio get larger, the algorithm starts to break down.  Since the
CW gets pulled back back by a percentage value of the FlightSize (50%),
perhaps it should also be increased by a percentage value of the
FlightSize, rounded up to the nearest multiple of the MSS.  Pick the
right value, and it won't kick in until you get a severely lopsided
ratio such as this example.  BTW, what MSS is being assumed at 10Gbs?
That will change the recovery time.  If you have a 64 Kbyte MSS, you are
going to recover a lot faster than with a 1500 byte MSS.  Hence my idea
that the discussion should focus on the size of the arithmetic increment.
And I think a very focused discussion like that could produce some
valid results in a fairly short time. 

			-David Borman, dab@bsdi.com