[e2e] TCP goodput as a function of connection count

Lachlan Andrew lachlan.andrew at gmail.com
Sun Apr 4 15:41:25 PDT 2010

Greetings Zartash,

AFAIK, multiple flows in download accelerators benefit their users
using the two mechanisms I mentioned in the final paragraph of my
email.  (a) On high bandwidth-delay product (BDP) paths with frequent
transient loss/congestion, they can overcome Reno's slow increase and
rapid decrease in rate, and (b) they can give their users more rate at
the expense of other users.

In the first case, something is gained by parallelism, but it could
more cleanly be gained by changing the congestion control algorithm of
a single flow.  In the latter case, I'd argue that nothing is gained
by the community as a whole, although of course something is gained by
the one with parallel flows.

This is just my understanding; I'd be happy to be corrected.


On 5 April 2010 08:05, Zartash Afzal Uzmi <zartash at lums.edu.pk> wrote:
> Hi Lachlan,
> Theoretically, what you mentioned makes good sense: it is convincing that
> bittorrent's benefit is realized by working with multiple paths and not just
> multiple connections. Practically, we do see simultaneous tcp connections
> bring benefit to the end user (in download accelerators, for example). These
> connections aren't on different paths, yet the end user benefits. Is that
> not contrary to the original intuition that nothing is gained by
> parallelism?
> Best regards,
> Zartash
> -----Original Message-----
> From: end2end-interest-bounces at postel.org
> [mailto:end2end-interest-bounces at postel.org] On Behalf Of Lachlan Andrew
> Sent: Sunday, April 04, 2010 3:07 AM
> To: tim at ivisit.com
> Cc: end2end-interest at postel.org
> Subject: Re: [e2e] TCP goodput as a function of connection count
> Greetings Tim,
> On a quick scan, the "TCP connection game" paper seems to deal with
> opening multiple connections over a single path.  The only benefits
> that generally gives are (a) working around Reno's inability to fill
> the path, and (b) providing a mechanism for unequal sharing of
> capacity.  The (social) benefit from bittorrent is the multiple paths,
> not just multiple connections.

Lachlan Andrew  Centre for Advanced Internet Architectures (CAIA)
Swinburne University of Technology, Melbourne, Australia
<http://caia.swin.edu.au/cv/landrew> <http://netlab.caltech.edu/lachlan>
Ph +61 3 9214 4837

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