FW: ISPs slowing P2P traffic...

Frank Bulk frnkblk at iname.com
Wed Jan 16 15:07:22 UTC 2008


The wikipedia article is simplified to the extent that it doesn't embed
actual practices.  Those are best obtained at SCTE meetings and discussion
with CMTS vendors.

A 10x oversubscription rate from residential broadband access doesn't seem
too unreasonable to me based in practice and what I've heard, but perhaps
other operators have differing opinions or experiences.

The '250' is really 250 subscribers in my case, but you're right, you see
different figures bandied about in regards to homes passed and penetration.

Frank

-----Original Message-----
From: owner-nanog at merit.edu [mailto:owner-nanog at merit.edu] On Behalf Of
Mikael Abrahamsson
Sent: Wednesday, January 16, 2008 1:07 AM
To: nanog at merit.edu
Subject: 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 at swm.pp.se




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