FW: ISPs slowing P2P traffic...

Mikael Abrahamsson swmike at swm.pp.se
Wed Jan 16 07:06:39 UTC 2008


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 at swm.pp.se



More information about the NANOG mailing list