[e2e] TCP "experiments"

Lachlan Andrew lachlan.andrew at gmail.com
Wed Jul 31 17:10:04 PDT 2013

On 1 August 2013 05:05, Marco Mellia <mellia at tlc.polito.it> wrote:
> If you want an example where a change would be not "fair", you can consider YouTube.
> Now they start to use more than one TCP connection to serve the video.

That is the canonical example of what is wrong with the approach of
TCPM.  TCPM is extremely reluctant to allow improvements to the
behaviour of a single TCP flow, and so users open multiple
connections.  Each flow is "standards compliant", but the net result
is IMHO much worse than if a single TCP flow could have more

Bob Briscoe has been arguing for a long time that we need to take a
broader view and consider "regulating" (or charging for) multiple
connections between a given pair of entities.  His particular solution
has had strong push-back from operators, but his point is entirely
valid.  Excessive inflexibility about what a single TCP flow is
allowed to do hinders progress without contributing substantially to
real-world fairness or performance.

Again, I'm not saying that there should be a free-for-all, with
unmonitored experiments.  We just need to remember that the aspect of
TCP congestion control that prevents congestion collapse is primarily
the shift from go-back-N to selective-repeat i.e., packet
conservation.  Changing almost any other aspect is unlikely to bring
the Internet crashing down.  ((Standard thought-experiment disclaimer


Lachlan Andrew  Centre for Advanced Internet Architectures (CAIA)
Swinburne University of Technology, Melbourne, Australia
Ph +61 3 9214 4837

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