I just wrote this mini-report on my meeting with the Optus@Home people
on Thursday, in response to a discussion on Oz-ISP and Link. Someone
was querying the reality of the upstream restrictions with HFC (Hybrid
Fibre Coaxial) cable Internet, and whether (as was suggested to them)
these restrictions had a regulatory origin.
- Robin
The upstream limits on HFC are partly physics and partly history.
Downstream you can get about 4 bits per Hz, due to the relatively low
noise. So a 6 MHz wide band carries about 30 megabits/sec.
Upstream, all the amplifiers from multiple branches of coax in the
fibre-serving area are mixing their outputs together, and you get more
noise. Also, they pick up noise entering the system from devices in the
home. The 10 to ~50 MHz range for upstream signals is electrically more
noisy in general, due to CB radio transmitters, remote-control toys etc.
Generally, you can get 1 bit per Hz.
The split-point of upstream vs. downstream is usually in the 50 to 65
MHz area in Australia, but is lower in the USA. Below 30 MHz may not be
usable, so they may only have 30 to 50 MHz for upstream. This means
about 20 MHz for upstream. Cable-modems and telephony share this
capacity.
Downstream, if you didn't have to carry pay-TV signals (7MHz per
analogue channel or 30Mbps =~5 channels of digital) then you could use
from about 65 MHz to 750 MHz for downstream. That is about 700MHz x 4 -
2.8 Gbps. Also, the system can be pushed to 1,000 MHz if they want so
there is no shortage of downstream capacity.
The split-point in the US is typically lower - 40-55 MHz for instance -
so they have less upstream capacity still.
The reasons are not regulatory, as far as I can see. They stem from
wanting to preserve lower analogue TV channel frequencies, and probably
from a profound sense of consumers being *consumers*. This view,
common in the towers of great corporates (I know, I was there in the
Optus boardroom, looking down and out on most of Sydney) is that
consumers are *viewing* *content* on the web, and are primarily
concerned with a *compelling* experience. This is the corporate view
of consumers as using the Internet like a television. It is partly
true, but not to the simplistic extent which is often believed. It is
partly a hunting-and-herding dream of millions of dumb consumers sucking
*content* and so becoming easily fed milk-cows to the billing system
which fattens the corporation and the dreamer's salary. In fact, many
people want to do all sorts of two-way things, like run web servers,
game servers, video-conferencing hubs and do video-conferencing with
their family and friends (and paying clients . . . .) in other
countries.
This *consumer* "TV" view probably contributed to the lousy allocation
of upstream frequencies both here and in the USA.
It is possible to change the amplifiers in a fibre-serving area and put
the split wherever you like, such as at 200 MHz or so. That fixes the
upstream problem! There are trickier methods as well, including using
individual sectors in the fibre-serving-area separately and sending
those upstream spectrums back on the one fibre via heterodyning
(frequency shifting).
I interviewed Milo Medin on Thursday, for a future article in
"Australian Communications" magazine. http://www.auscoms.com.au/
I am yet to get an answer as to why there are no current plans to offer
the service to flats, including those already with Optus HFC cable.
Their concerns about people running high volume servers at home is very
real. There is a nasty program called Napster http://www.napster.com
which anyone can run on their PC, which turns their PC into a server for
all their MP3 files. (It does not tell the person this.) Those files
become indexed in the Napster server and so their machine becomes a
server for people all over the world downloading multi-megabyte MP3s
from the person's machine.
On an HFC system, this could easily choke the upstream bandwidth - hence
the 128kbps limit on each connection. Still, there are problems, and
@Home need a simple policy anyone can understand to limit the problem -
and that policy is "No Servers".
The proposal to limit upstream traffic on a longer-term basis seems
sensible to me. This means you could still send large email attachments
quickly (but not hundreds a day) and can still run servers which are not
in general doing a lot of traffic. If you overdo it, your upstream
capacity becomes more limited for a day or so. For a "residential"
service, this makes sense to me.
I questioned them about business services - something they mentioned
almost nothing about without prompting. In the US, most "@work"
business services are via 1.5 Mbps ADSL or 144kbps "IDSL". This could
be because they are yet to fully control the upstream data-path as they
would like. http://work.home.net/
Clogging the upstream path prevents acknowledgment packets from getting
through, so this upsets the downstream too.
The impression they gave me, after my pep-talk on the need for
"business" services is that they will do this in time. For now, they
are focusing on this very consumerish "viewing" service to start with,
and will develop variations on this for more server activity, and later
for "business" services" when they have the software they want in their
routers and the cable-modem gear at the headend.
By "business" services, I mean the ability to do what you like on HFC,
no filtering, fixed IP addresses and subnet ranges of IP addresses, and
pay reasonably for it - including by volume. Also, perhaps the ability
to reserve some bandwidth and to pay according to traffic in the two
directions and by time of day, and perhaps even where the traffic is
going to or coming from.
I intend to get some answers about their worrying use of cache data to
target their customers with advertisements - although they assured me
they would never sell that data to anyone else.
http://www.home.com/about/network.html
They shouldn't be collecting such content-related usage information at
all, as far as I am concerned.
- Robin
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Robin Whittle [EMAIL PROTECTED] http://www.firstpr.com.au
Heidelberg Heights, Melbourne, Australia
First Principles Research and expression: Consulting and
technical writing. Music. Internet music
marketing. Telecommunications. Consumer
advocacy in telecommunications, especially
privacy. M-F relationships. Kinetic sculpture.
Real World Electronics and software for music including:
Interfaces Devil Fish mods for the TB-303, Akai sampler
memory and Csound synthesis software.
===============================================================
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