[e2e] opening multiple TCP connections getting popular

Keith Moore moore at cs.utk.edu
Thu Aug 30 09:16:39 PDT 2007

[this is a resend...I think the list filtered my mail first time around.]

It seems to me that if "fairness" is defined by how well hosts limit the
number of concurrent flows then there's a problem with the definition. 

>From an application's perspective, there are valid reasons for having
multiple flows between two endpoints, which don't involve trying to get
more bandwidth than is available to other hosts.

Ideally there would be little difference in the aggregate bandwidth of
10 flows between two endpoints versus a single flow between those two
endpoints.  The thing to do is to work on making that so, not by
pessimizing multiple flows so that they work as badly as a single flow,
but by improving congestion control so that it does a better job of
adapting to network conditions while ignoring transient packet losses
unrelated to network congestion.

And really, hosts/stacks/apps that do a better job of accurately
detecting the difference between network congestion and transient packet
losses ought to get more bandwidth for their trouble.   Otherwise
there's a disincentive to implement better algorithms.


Bob Briscoe wrote:
> e2e-interest folks,
> This product is being very aggressively marketed:
> <http://www.speedbit.com/video%5Faccelerator/>
> It opens 10 HTTP/TCP connections to accelerate video downloads -
> essentially using the well-known broken feature of TCP (see the I-D
> below) to enable one user to compete more aggressively for the same
> bandwidth against other users. But it flies below the limit of 10
> concurrent half open connections added to Windows XP SP2 - claimed to
> be added to slow down worms but also limiting p2p filesharing clients.
> Amazingly, these guys are approaching ISPs to re-sell this product -
> so their customers will just be competing more aggressively with each
> other and largely end up back where they started. It's worth reading
> the Business Week article linked off the above page to see just how
> convincingly this is being marketed - They fooled the technology
> assessment people in at least one large ISP (mentioning no names).
> If you're tempted to poke fun at all these people because they clearly
> don't understand, I actually think we should be chastened ourselves.
> Why shouldn't app-layer people expect the transport layer to correctly
> handle fairness?
> To quote the Internet Draft "Flow Rate Fairness: Dismantling a Religion"
> <http://www.ietf.org/internet-drafts/draft-briscoe-tsvarea-fair-02.pdf>
> "...flow rate fairness isn't even capable of reasoning about questions
> like, "How many flows is it fair to start between two endpoints? ...
> ...there will certainly be no solution until the networking community
> gets its head out of the sand and understands how unrealistic its view
> is; and how important this issue is--a conflict between the vested
> interests of real businesses and real people."
> King Cnut commanded the tide not to wash over him sitting on his
> throne on the English beach, but at least when the experiment failed
> he humbly accepted he was subject to greater powers, never wearing his
> crown again. I'm worrying away at the IETF to work on a proper
> solution to the TCP-fairness problem, rather than merely issuing the
> decree that RFC2616 HTTP/1.1 clients should observe a 2 connection
> limit to each server.
> Bob
> ____________________________________________________________________________
> Bob Briscoe, <bob.briscoe at bt.com>      Networks Research Centre, BT
> Research
> B54/77 Adastral Park,Martlesham Heath,Ipswich,IP5 3RE,UK.    +44 1473
> 645196

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