Contention/Oversubscription maths

William Herrin bill at
Fri May 27 19:52:47 UTC 2011

On Thu, May 26, 2011 at 6:48 PM, Adam Armstrong <lists at> wrote:
> Do any of you have any pointers on how to go about predicting usage for
> high-speed ethernet access?
> Finally, what do people think of selling a 1G service with 1G backhaul (and
> potentially 10s or 100s of customers buying this service alongside n*100s of
> customers with 100M service)?

Hi Adam,

I think you better have a PPoE concentrator somewhere or you're going
to deal with a flood of broadcast, virus and other trash traffic. I
also think expecting fewer than 1% of your residential customers to
P2P at once is borrowing trouble.

I've been out of the ISP game too long to give you hard numbers at
today's network speeds, but back when I was in the game, a 100:1
oversubscription ratio for residential DSL was around the boundary of
what customers described as poor quality and slow. That number was
steadily trending downward, not up, though the official villain then
was Bit Torrent instead of Netflix.

On the other hand, it might be an interesting experiment to take a
utility company approach... Sure we'll give you a 200 amp service with
only 1000 amps in the neighborhood, but you don't pay for the 200 amp
service you pay for the consumption of kilowatt hours. On the other
hand, heat pumps don't get hacked and start drawing the full 200 amp

Bill Herrin

William D. Herrin ................ herrin at  bill at
3005 Crane Dr. ...................... Web: <>
Falls Church, VA 22042-3004

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