[e2e] opening multiple TCP connections getting popular

Bob Briscoe rbriscoe at jungle.bt.co.uk
Sat Sep 1 02:02:37 PDT 2007


I composed responses yesterday to each of your points, but I've realised 
there's no purpose in sending them until the underlying terms of reference 
are mended...

At 08:00 31/08/2007, Joe Touch wrote:
>Bob (et al),
> >> (and, as others have noted, it's not
> >> clear we _need_ to do anything).
> >
> > Tell that to the CEO of any network operator. I think you're saying
> > there's not an engineering problem. But that's because resource
> > allocation problems are economic problems not engineering problems...
>No - I'm saying it isn't a problem. Whether it's economic or otherwise,
>as others have noted, not being 'fair' depends on an agreed concept of
>fairness. We have one now - per-TCP connection, relative to RTT. That's
>not perfect, but it is a definition, and it does work.

Well, most people who have entered this debate (mosly on tsvwg) have tried 
to distance themselves from ever having been definite about per-TCP 
connection/RTT as the agreed measure.

Of course there's not a problem... if you're measuring it the way you 
are... but that's because the measure you're using isn't a relevant measure 
- fairness is a social science issue so you need a social or economic 
measure. Otherwise your judgement of whether 'it works' is circular...

Imagine a country had a tax system based on the number of transactions 
entering and leaving a person's bank accounts.
* I'm saying such a metric doesn't produce a fair taxation system (e.g. 
high earners stuff more money through less transactions).
* By analogy, by sticking with transaction count as a measure, you're led 
to argue that there's not a problem. You can cite surveys of the 
transaction count into people's bank accounts that show people are being 
taxed in fair proportion to this count, and further, you're led to say that 
there can't be a problem because the spread of the count of transactions 
between most and least is pretty small.

If you look instead at the different volumes of congestion that users cause 
against how much each is contributing to the system, you should be able to 
see there is a huge problem. There's also a far greater spread of 
congestion volume caused by different users than is warranted by any value 
they get from causing it - many orders of magnitude between the lowest 
quartile and the highest, but the spread of contributions is probably 
within an order of magnitude.

It's not just flow rate. Flow rate must be weighted by the prevailing 
congestion at each instant and the result accumulated over /time/. Then 
attributed to each /economic entity/. That's congestion volume per 'user'.

And, if we go straight to congestion volume without passing through flow 
rate, the resulting accountability system is really simple.

Ditch flows.


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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