When a broadband service says they have a contention ratio of say 50:1
what is it that the 50 customers are sharing? If all 50 customers are on
the ISP's 512kbps service they can't be sharing a single 512kbps
connection as you would notice slow down all the time. I'm guessing it
is a much larger "pipe?"

tia

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On Wed, 28 Sep 2005 21:46:45 GMT, "Cullen Skink"
<newsgroups@SOMETHINGFISHYukwebhost.com> wrote:

forget "50 customers"

50:1 is a ratio. Lets call it 25600 : 512 instead. Or 450:9, etc.

Contention is defined as the amount of bandwidth sold to customers
divided by the amount available at the point in question.

So if 400 people with 1M lines are contended 50:1 there will be a
connection capacity of 400 * 1 / 50 = 8 Mbits/s.

Also note that in BT ADSL the ratio is "up to" 50:1 and generally held
to be about 40% of that level in practice.

Phil
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Cullen Skink wrote:
Nope, right first time. It relies on all 50 customers not requiring
bandwidth simultaneously but if they did the connection speed would slow
to 10kbps for each of them until demand started to drop again.

--
Tony

"I did make a mistake once - I thought I'd made a mistake but I hadn't"
Anon

No, the critical factor is the amount of traffic on your network, which
depends on the types of user and the amounts of bandwidth they are
consuming. For example, if you had a business park and a housing
estate sharing the same contended ethernet ring on a Cable TV network,
you'd expect the (small number of) business users each to be consuming
lots of bandwidth between 9-12 and 1-5, with little week-end usage, and
then the (large number of) consumers each to be consuming smaller
amounts of bandwidth from 4-10 and at week-ends.

Nick

On Thu, 29 Sep 2005 12:43:35 +0100, Mark <codvimyst@yahoo.co.uk>
wrote:

DSLAM to ATM "cloud" is the stated produce contention as far as BT are
concerend.

"reselling" is a misnomer I suspect, but yes if the contention is
greater on the BT Central then it will be the limiting factor not the
exchange backhaul contention. Hence Plusnet's "contention on the
Plusnet network" quoted in addition to the "BT contention".

In practice we have seen both exchange contention "Red VPs" and ISPs
with congestion problems (Demon Home)

With Centrals at £240/month per Mbit/s I suspect some Central
contentions are running well over 50:1 to make it pay. Doesn't matter
if the user demands are modest.

Phil
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Tony Raven wrote:
Surely not. Even with 4 people using it at the same time you would
notice a big drop off in performance and that doesn't seem to happen. If
one person was connected 24/7 doing downloads how could anyone else use
it? I think I'm missing something. :-)

On Thu, 29 Sep 2005 22:54:41 GMT, "Cullen Skink"
<newsgroups@SOMETHINGFISHYukwebhost.com> wrote:

the 50 people thing is the error. The pipe might be 10 Mbits/s so it
needs 20 512k users at maximum download to fill it. At 50:1
contention there will be *up to* 1000 users able to use it, so 20
assholes can make life painful for a lot of people.

The rather feeble 2M backhauls used by datastream operators in the
early days were often completely utilised by a single 2M user so
nobody ever say their rated speed unless they happened to be the only
one using it.

Phil
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AOL - the unlimited ISP of choice for heavy downloaders.

Phil Thompson wrote:
Thanks, the fog is lifting, I think. :-) I'm guessing they try to keep
the "up to" 1000 users much lower than that then as at that rate only 10%
online at any time would swamp it and 10% seems a lowish figure.

Was thinking back to that as well. When BB was first being introduced
there was talk of it slowing down with only a few users online at a time
which is what got me thinking about it as it doesn't "appear" to be the
case now.

Is the contention ratio per exchange or is it configurable across the
network? I'm on datastream which probably makes a difference.

On Fri, 30 Sep 2005 09:36:14 GMT, "Cullen Skink"
<newsgroups@SOMETHINGFISHYukwebhost.com> wrote:

its not 10% online its 10% going flat out, which is different. Its
built for web surfing and collecting email, which aren't flat out
applications.

contention ratio is strictly per virtual path, there may be several of
them handling IPstream. Business services should be on a different VP
as they have different contention (20:1 vs 50:1). For datastream there
is likely to be one VP and its likely to be much smaller due to small
number of users of one ISP on the exchange.

Phil
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AOL - the unlimited ISP of choice for heavy downloaders.

Cullen Skink wrote:
Being on-line and using bandwidth are not the same thing. Except for
streaming, gaming and file download you are rarely continuously using
bandwith so it works on the principle that those 4 people will not
actually being continuously overlapping in their demand for bandwidth.
You might hit short slow downs during brief contentions and if everyone
wanted to use bandwidth at once they would notice a slowdown.


--
Tony

"I did make a mistake once - I thought I'd made a mistake but I hadn't"
Anon

Cullen Skink wrote:

Its not 50:1 but the numerical equivalent of a larger ratios
i.e. something like 50x40:1x40 i.e. 2000:40 or something like that.
That means 40 users can go on full 512kpbs speed
without problem. The 41st user will start taking a little bit
of bandwidth away from all the other users.

But let me emphasise there has and never will be a shortage of bandwidth.
95% of all fibers laid are unlit.
ADSL contention is complete crap dreamt up by POTS management
when bandwidth was scarce. Which is no longer true!
Technology has progressed rapidly to the point that the same
fiber can deliver 100 times and then 1000 times and then 10,000 times
or more of the capacities available when they were first laid.
Thus 95% are unlit with any kind of laser beam.
Crap POTS management are still trying to milk the public
with bandwidth scarcity stories, when in fact, they haven't lit
their own fibers. Incumbant operators like BT$ should be broken
up and the markets deregulated and the task of
delivering THz bandwidth to the desktop should be left to
more qualified people who would rush in with THz equipment
if the markets were opened up.

Bring on LLU and we shall see!

BWAHAHAHAHAHAHAHAHAHAHA!

Tony Raven wrote:
Yeah sorry I meant 4 people actually using the connection.

On Wed, 28 Sep 2005 21:46:45 GMT, "Cullen Skink"
<newsgroups@SOMETHINGFISHYukwebhost.com> wrote:

It's a bit like trying to explain how 5,000,000 cars can use the UK
road network at the same time without any of them dropping their
average speed below 40mph ... apart from isolated areas where the
average speed might drop to 10mph or so.

Does that help?

Jake

Muxton wrote:
The M25 can hold approx 20,000 vehicles travelling at 70mph and keeping
the recommended 2s separation. There are 28 million registered vehicles
in the UK giving the M25 a contention ratio of 1400:1. Fortunately not
everyone wants to use the M25 at once although it often seems that way ;-)

--
Tony

"I did make a mistake once - I thought I'd made a mistake but I hadn't"
Anon

"7" <website_has_email@www.enemygadgets.com> wrote in message
news:fTi%e.119098$G8.57087@text.news.blueyonder.co .uk...
OK.

The main complication is that there isnt just 1 backhaul - there can be
several and each can have its own contention.

If you are with an ISP using Datastream, then contention happens in a
dedicated VP for that ISPs customers on that DSLAM - and the max bandwidth
on on the VP is 10 Mbps or so.

IPstream ISPs seem to share a bigger common pipe, but i think that different
IPstream style services such as business vs consumer are kept separate.
Agreed.

the expensive thing to do is dig the hole and put the fibre cable in - which
is why telcos either put in large cables with plenty of spare cores for
possible future use and / or put down something like blown fibre where extra
cores can go in easily later.

but just because all that spare fibre is out there doesnt mean that a) its
cheap to get at and b) it goes to the right places via the right routes....
And whenever i plan a new network there always seems to be a bunch of
awkward holes in the coverage somewhere.

but the equipment to go on the end of the fibre isnt cheap either - and
telcos are being careful with money for the last few years.

No. There is no point taking away the contention at the 1st hop aggregation
point and just pushing it back further into the network if that adds a lot
to the systems cost and doesnt increase overall capacity.

you can certainly argue that the contention ratio you live with isnt good
enough, but inpractice contention only seems to be an issue in small parts
of the network at any one time. Not much consolation if that is your
exchange tho.....

in practice contention ratios quoted are all worst case, and i think that
real life rarely gets close to the quoted numbers.

Again no, or not really. a lot of fibre is fairly new, and this assumes
fibre went in a long time ago.

FWIW some new gear at work support 200 * 10G on a pair of fibres - but we
would only use that on long haul routes. better stuff is around but a lot
more expensive.

Bleeding edge systems from 5 to 10 years ago could do 32 or 64 * 10G then,
so there hasnt been a massive step increase in theoretical capacity for
practical systems that get deployed. A lot fo that may be due to the dot-com
troubles over the last few years making high end telco gear much harder to
sell, and making manufacturers cut back on R+D.

For short distances it is cheaper to use lower capacity stuff, since the
hardware needed is more expensive than using metro DWDM or just extra fibre
cores

you have to remember that it doesnt do any good to open up the pipe unless
you uprate all the server farms as well - or you just move the contention
around.

the only thing likely to alter that assumption is a change to the current
use of the Internet where traffic is almost all point to point flows.

Now if a broadcaster could send high quality streaming video using
multicast, so that the network replicates the data - then getting rid of
contention might pay off big time - but that needs ISPs to understand how to
do it, be willing to pay for the equipment and other complications, and
figure out how to cover the costs in some way.
LLU only fixes the last mile loop - contention is about backhaul bandwidth
into the aggregation point - so how does that help.

FWIW all the companies doing LLU seem to be Telco types - so if this is a
"big conspiracy" then LLU wont fix it.
Regards

stephen_hope@xyzworld.com - replace xyz with ntl