[e2e] TCP un-friendly congestion control

[Raghurama 'REDDY']

IMHO the different flavors of TCP (Linux 2.4 TCP, HPTCP and Scalable
TCP; I don't know enough about FAST) differ primarily in their response
to loss events.  So if there are no loss events either because of
adquate buffering in the network, or because the host buffers are sized
just right, then it is possible to get into an "ideal" condition,
especially on a clean path, where it is possible to get close to peak
performance irrective of the flavor of TCP used.  In this situation
there will be no probing (and hence no saw-tooth behavior).

My guess is that it was more likely that the socket buffers were sized
just right to avoid any probing/packet drops.

Best Regards,

--Raghu Reddy

From:	SMTP%"rhee at eos.ncsu.edu"  "Injong Rhee"  9-JUN-2003 12:57:42.76
To:	end2end-interest at postel.org
CC:	
Subj:	RE: [e2e] TCP un-friendly congestion control 

I came to know this work recently too.  I suspect that the high performance
migth be due to a large buffer space some place on DropTail router network.
In the droptail router with buffer space K, the congestion window drops down
to (B*D + T)/2. If T is as much as B*D, then TCP drops its window down to
B*D which is the capacity of the link. If RED is used, the result will be
quite different, i believe because packet drop will happen well before the
buffer fills up. Also DropTail with a large buffer adds a lot of congestion
delays.

 Could somebody confirm the amount of router buffer space at the bottleneck
of this path and whether RED is being used? whether the buffer space is
pooled or dedicated to a port? At some point, Tom Kelly reported a very
little buffer space. But that could have been changed.

-----Original Message-----
From: end2end-interest-admin at postel.org
[mailto:end2end-interest-admin at postel.org]On Behalf Of Richard Carlson
Sent: Monday, June 09, 2003 11:04 AM
To: end2end-interest at postel.org
Subject: Re: [e2e] TCP un-friendly congestion control


As chair of the Internet 2 Land Speed Record judging committee, I can
confirm that TCP over long fat networks is not hopeless.  The last 2
records, using IPv4 and IPv6, show that hosts can push the network to the
limit.  For the latest IPv4 record a team from the US and Europe ran Iperf
for 3700 seconds (yes just over 1 hour) between 2 PC's with 10 Gigabit
Ethernet NICs.  They achieved a throughput rate of 2.3 Gbps, with the
connection being limited by a transatlantic OC-48 link.  The latest IPv6
record is being processed now, but it is equally impressive.  See the
I2-LSR web page http://lsr.internet2.net for details.

Another thing to consider, Les Cottrell from SLAC ran some tests with these
10 Gig NICs and tested the standard Linux 2.4 TCP, FAST TCP, HPTCP, and one
other high performance implementation.  These tests showed no difference
between any of the TCP implementations over 1 particular network path.  If
Les is on this list maybe he can provide a pointer to these results.

Rich

At 05:26 PM 6/6/03 -0400, Craig Partridge wrote:

>In message <20030606140028.A59651 at xorpc.icir.org>, Luigi Rizzo writes:
>
> >exactly -- that's the whole point, the packet rate is so high that
> >there are many chances to have occasional losses anywhere in the
> >system, not just due to the channel but even because of operating
> >system issues on some of the intermediate boxes or end nodes.
>
>OK, let me get on my high horse here for a moment.
>
>The original poster asserted that in an environment where the network
>went at 1 Gbps and had 50ms of delay, TCP was hopeless.
>
>The point I was trying to drive home is that it is not hopeless.  That
>you have to define the environment far more carefully before you assert
>that TCP can or cannot do the job.  One of my frustrations these days is
>people who fail to be careful.  I was trying to encourage care in the
>problem statement.
>
>Thanks!
>
>Craig

------------------------------------

Richard A. Carlson                              e-mail: RACarlson at anl.gov
Network Research Section                        phone:  (630) 252-7289
Argonne National Laboratory                     fax:    (630) 252-4021
9700 Cass Ave. S.
Argonne,  IL 60439


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