From: "DaZZa" <[EMAIL PROTECTED]>
> On Tue, 8 Aug 2000, John Wiltshire wrote:
>
> > > Sure - 2 meg - SHARED_ access - and if you have, say, 20
> > > people on each
> > > cable segment - that 2 meg disappears pretty quickly.
> >
> > This is based on the somewhat false assumption that all people are using
> > their full bandwidth all of the time. Given that the average ISP has at
>
> I've got news for you - as more and more people get onto HFC systems,
> they'll _all_ expect to be able to run streaming video all day, and
> download gigabytes of music and files all day etc. It's already happening
> now. Ask Optus. There's a guy at work here - he PC anywhere's his PC, from
> work, to home, and STILL runs stuff all day.
That's why Telstra has caps on both bandwidth and usage. If Optus don't
then they deserve what they get. Note that Telstra has now bandwidth capped
everything but the top business plan.
> > least 10 users per modem and at least 10 times the number of modems that
> > their external bandwidth can handle I think 20 people sharing a cable
> > segment (which can handle 33Mb) is a pretty fair amount. If it got up
to
> > about 100 I'd start to get a little worried.
>
> 33 mb is a bit of an exaggeration. Some of that bandwidth is reserved for
> voice signalling. Some is reserved for TV signallnig. Only 2 meg _per
> segment_ is reserved for data.
The cable modem spec has 33mb available so it is no exaggeration. For Optus
to be using standard "off the shelf" modems they have no choice but to
allocate the spectrum. 33mb is not the bandwidth of the cable - it is the
bandwidth defined by the standard used by Optus and Telstra.
Voice and TV signalling go on a separate channel. I'm not sure where you
got the 2mb number from.
> > > The difference between ADSL and HFC systems is that HFC system uses a
> > > _shared_ carrier - it's more of a broadcast system - and ADSL is a
> > > _direct_ connection - you get your 1.5 meg ALL the time - not
> > > just when none of your neighbours are using the net as well as you.
> >
> > Except for the fact that all ADSL lines still come into an exchange and
you
> > get a shared medium there. If you are lucky then they have the
bandwidth
>
> And you think HFC systems are any different? Hell, even an E1 connection
> to the net will bottleneck _somewhere_ - it's simply the lay of the land -
> there is a balance between effectiveness and cost - with cost winning more
> often than not.
I never said HFC was any different (or an E1 for that matter). I'm just
saying that the idea that ADSL isn't shared is very short sighted.
> > from the exchange to support the number of ADSL users they plug in. You
> > have to assume they are running better than 100Mbps equipment in the
> > exchange before they can exceed the capacity of HFC systems. The idea
that
> > ADSL gives you the bandwidth to yourself and cable doesn't is such a
mind
> > boggling oversimplification it's almost a delusion.
>
> {laughter} Just how much trunking bandwidth do you think the average
> telephone exchange has? Hint - 100 Mb/s is, except in the case of a tinpot
> shed out the back of beyond {waves to Jon Biddel} is the very _bottom_ end
> of the spectrum. Remember, once it hits the exchange in a digital network,
> dedicated bandwidth for data is _not_ required, because it's all a packet
> switched network anyway.
It's not the trunking bandwidth that is the problem. The bottleneck occurs
between the ADSL decoding equipment and the packet switched network. A
separate hint: you need about 3kb to handle a voice channel. You can
handle the voice load for an entire exchange (10000 customers) on about a
100Mb switched network. Telstra exchanges don't support every customer
calling at once. In fact, they don't support anything close to that.
Also, on a packet switched network what do you think with have the higher
priority - voice packets or BigPond packets? Packet switched doesn't mean
all packets get equal treatment.
> > Having been connected to BPA (cable) for a while now, I can say that the
> > real bandwidth problems have been with the Big Pond Direct connection
from
> > Perth to the USA and never with the saturation of the local loop.
>
> So you're lucky - you don't have many users in your local cable segment -
> the same as I am with Optus. But I know people who are on _busy_ bigpuddle
> cable segments - and the service is terrible. ADSL will make them much
> happier.
Probably. BP has larger problems with their network though. I still get
20% packet loss to any server on cerf.net (independant of time of day). Go
figure.
> > Occasionally there are problems with the local servers or with routing
but
> > I've never gotten less than my capped speed between my machine and the
local
> > router.
>
> I repeat - you're lucky. Not everyone is so well off.
Ok. Fair enough. I'm just commenting on my experiences.
John Wiltshire
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