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RE: FW: ISPs slowing P2P traffic...
On Tue, 15 Jan 2008, Frank Bulk wrote:
Except that upstreams are not at 27 Mbps (http://i.cmpnet.com/commsdesign/csd/2002/jun02/imedia-fig1.gif show that you would be using 32 QAM at 6.4 MHz). The majority of MSOs are at 16-QAM at 3.2 MHz, which is about 10 Mbps. We just took over two systems that were at QPSK at 3.2 Mbps, which is about 5 Mbps.
Ok, so the wikipedia article <http://en.wikipedia.org/wiki/Docsis> is heavily simplified? Any chance someone with good knowledge of this could update the page to be more accurate?
And upstreams are usually sized not to be more than 250 users per upstream port. So that would be a 10:1 oversubscription on upstream, not too bad, by my reckoning. The 1000 you are thinking of is probably 1000 users per downstream power, and there is a usually a 1:4 to 1:6 ratio of downstream to upstream ports.
250 users sharing 10 megabit/s would mean 40 kilobit/s average utilization which to me seems very tight. Or is this "250 apartments" meaning perhaps 40% subscribe to the service indicating that those "250" really are 100 and that the average utilization then can be 100 kilobit/s upstream?
With these figures I can really see why companies using HFC/Coax have a problem with P2P, the technical implementation is not really suited for the application.
-- Mikael Abrahamsson email: swmike@xxxxxxxxx