[101711] in North American Network Operators' Group
RE: FW: ISPs slowing P2P traffic...
daemon@ATHENA.MIT.EDU (Mikael Abrahamsson)
Wed Jan 16 02:17:32 2008
Date: Wed, 16 Jan 2008 08:06:39 +0100 (CET)
From: Mikael Abrahamsson <swmike@swm.pp.se>
To: nanog@merit.edu
In-Reply-To: <!&!AAAAAAAAAAAuAAAAAAAAAKTyXRN5/+lGvU59a+P7CFMBAN6gY+ZG84BMpVQcAbDh1IQAAAATbSgAABAAAAAyoOwk2Gc8R6phhn16ODBaAQAAAAA=@iname.com>
Errors-To: owner-nanog@merit.edu
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@swm.pp.se
