e'splain contention

OK, so I'm on 512kbit ADSL with a 50:1 contention ratio and my ISP is a
ficticious provider called Wanapoo.

Let's now say that I'm downloading a single very large file, from a very
reliable and stable source and that I'm using the maximum 512kbits per
second to get this file (a 'distro' or a ripped DVD - it makes no difference
to this example.).

Let's assume that I'm the only person logged on at my exchange for now.

I'm maxing out my download and everything is fine. Now, someone else from
the same exchange logs on to their own 512kbit line and starts to download
another file from another very reliable and stable source.

We've now got two download in progress - both are dedicated to pulling data
from the sources as fast and consistently as they can.

What are the factors involved in this:
e.g.

Will both customers be on the same 'pipe' from the same ISP.

What if one is on 'pipe1' and the other is on LLU (another 'pipe'
involved'?)

Is the 50:1 line, in reality, a (512kbit * some factor) line - so that
neither download will realise that someone else is sharing the same 'pipe'?

Will I end up with a max/2 download speed?

How do things change if the other downloader is a 2Mbit line - does this
mean he's on a different circuit, so that we are not affected by each
other - do we still share a common 'pipe'?

I'm interested in actual technical info rather than marketing speak.

Thanks for anyone that can answer this or point me to the right links.

Joe Butler wrote:
> OK, so I'm on 512kbit ADSL with a 50:1 contention ratio and my ISP is
> a ficticious provider called Wanapoo.

Fictious? are you sure? :-)

On Wed, 11 May 2005 19:54:48 +0100, "Joe Butler"
<(E-Mail Removed)> wrote:

>Is the 50:1 line, in reality, a (512kbit * some factor) line - so that
>neither download will realise that someone else is sharing the same 'pipe'?

exactly, on BT IPstream you might be sharing a "virtual path" that is
perhaps 10 Mbits/s so it needs 20 users on that pipe to be going full
tilt before they start to impact each other.

>Will I end up with a max/2 download speed?

only if you are a Tiscali / NTL / Tesco user provided with a 512k
connection to the exchange (even then 2M is more likely).

>How do things change if the other downloader is a 2Mbit line - does this
>mean he's on a different circuit, so that we are not affected by each
>other - do we still share a common 'pipe'?

in ye olde days the office 20:1 products were on separate pipes, so 2M
and 1M coexisted but were separate to 512k residential. Don't know
what happens now, whether 2M, 1M and 512k residential users are all
packed in the same pipe or kept separate. If the pipe is big enough
and the sharing mechanism is "fair" it won't matter.

Phil
--
Tiscali - dialup speeds at Broadband prices.
AOL - the unlimited ISP of choice for heavy downloaders.

On Wed, 11 May 2005 19:07:07 UTC, "Beck"
<(E-Mail Removed)> wrote:

> Joe Butler wrote:
> > OK, so I'm on 512kbit ADSL with a 50:1 contention ratio and my ISP is
> > a ficticious provider called Wanapoo.
>
> Fictious? are you sure? :-)

No, he said 'fictitious'!

--
[Kenism - a condition by which the sufferer experiences an inability
to give concise answers, express reasoned argument or opinion.
Usually accompanied by silly noises and gestures, and frequent use
of the word 'fanboy' (although he calls it 'words')]

Bob Eager wrote:
> On Wed, 11 May 2005 19:07:07 UTC, "Beck"
> <(E-Mail Removed)> wrote:
>
>> Joe Butler wrote:
>>> OK, so I'm on 512kbit ADSL with a 50:1 contention ratio and my ISP
>>> is a ficticious provider called Wanapoo.
>>
>> Fictious? are you sure? :-)
>
> No, he said 'fictitious'!

argh damn the lack of spellchecker :-)

"Joe Butler" <(E-Mail Removed)> wrote in message
news:d5tken$i4c$(E-Mail Removed)...
> OK, so I'm on 512kbit ADSL with a 50:1 contention ratio and my ISP is a
> ficticious provider called Wanapoo.
>
> Let's now say that I'm downloading a single very large file, from a very
> reliable and stable source and that I'm using the maximum 512kbits per
> second to get this file (a 'distro' or a ripped DVD - it makes no
difference
> to this example.).
>
> Let's assume that I'm the only person logged on at my exchange for now.
>
> I'm maxing out my download and everything is fine. Now, someone else from
> the same exchange logs on to their own 512kbit line and starts to download
> another file from another very reliable and stable source.
>
> We've now got two download in progress - both are dedicated to pulling
data
> from the sources as fast and consistently as they can.
>
> What are the factors involved in this:
> e.g.
>
> Will both customers be on the same 'pipe' from the same ISP.

it depends - there are 2 basic sets of BT ADSL service (IPstream and
datastream) + any SDSL services. The way these are set up varies by
service - some are partitioned, some seem to just share a big pipe.

But - yes if they are at the same speed and the same service- unless the ISP
uses more than 1 pipe type (and a lot of ISPs have more than 1 different
underlying BT service type in use).

actual pipe sizes can be set by the ISP for Datastream, or is shared for
IPstream across multiple ISPs and (probably) different ADSL link speeds.
>
> What if one is on 'pipe1' and the other is on LLU (another 'pipe'
> involved'?)

if the 2 users connect to different domains (eg ipstream and LLU from
provider X), then the "contention" happens in 2 separate domainsand the
users dont affect each other.

same thing happens if 1 or both are Datastream, since each Datastream
provider gets dedicated bandwidth to each DSLAM, for each speed of ADSL
used.

Not sure if traffic for different speed links and different contention
ratios if split for IPstream, but different contention ratios would be
difficult if not.
>
> Is the 50:1 line, in reality, a (512kbit * some factor) line - so that
> neither download will realise that someone else is sharing the same
'pipe'?

yes - but given the "lumps" that bandwidth from the core network to the
DSLAM are provisioned, then the effective contention ratio tends to be a lot
lower.
>
> Will I end up with a max/2 download speed?
>
Maybe in worst case - but worst case should be unlikely.

However, different apps and different IP stacks tend to react differently to
the discard patterns or delays that will build up, so the sharing may not be
even.

For example, if you run several TCP connections, and your "contender" runs
one, you may get a bigger share of the cake.

> How do things change if the other downloader is a 2Mbit line - does this
> mean he's on a different circuit, so that we are not affected by each
> other - do we still share a common 'pipe'?

dont know with IPstream. yes with datastream.
>
> I'm interested in actual technical info rather than marketing speak.
>
> Thanks for anyone that can answer this or point me to the right links.

There must be better service descriptions, but have a look at the BT price
list and SINET - there is a lot of techie info buried in the notes.
http://www.serviceview.bt.com/list/c...cs/maintoc.htm
http://www.sinet.bt.com/
--
Regards

Stephen Hope - return address needs fewer xxs

"Phil Thompson" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> On Wed, 11 May 2005 19:54:48 +0100, "Joe Butler"
> <(E-Mail Removed)> wrote:
>
> >Is the 50:1 line, in reality, a (512kbit * some factor) line - so that
> >neither download will realise that someone else is sharing the same
'pipe'?
>
> exactly, on BT IPstream you might be sharing a "virtual path" that is
> perhaps 10 Mbits/s so it needs 20 users on that pipe to be going full
> tilt before they start to impact each other.

And in reality he would share that with 1000 users?
Ie 50 users share each 512 kbit (0.5Mbit) so 10Mbit is
20 times that 20X50=1000
>
> >Will I end up with a max/2 download speed?

What does max/2 mean?

>
> only if you are a Tiscali / NTL / Tesco user provided with a 512k
> connection to the exchange (even then 2M is more likely).

You seem to know what he is talkling about could you explapin?
>
> >How do things change if the other downloader is a 2Mbit line - does this
> >mean he's on a different circuit, so that we are not affected by each
> >other - do we still share a common 'pipe'?
>
> in ye olde days the office 20:1 products were on separate pipes, so 2M
> and 1M coexisted but were separate to 512k residential. Don't know
> what happens now, whether 2M, 1M and 512k residential users are all
> packed in the same pipe or kept separate. If the pipe is big enough
> and the sharing mechanism is "fair" it won't matter.


Different packages ofthen have diferent contention ratios, however
if it is the same c/r different speeds could be shareing the same pie.
Assunimg the pie was big enough.

>
> Phil
> --
> Tiscali - dialup speeds at Broadband prices.
> AOL - the unlimited ISP of choice for heavy downloaders.

On Wed, 11 May 2005 19:54:48 +0100, "Joe Butler"
<(E-Mail Removed)> wrote:

>OK, so I'm on 512kbit ADSL with a 50:1 contention ratio and my ISP is a
>ficticious provider called Wanapoo.
>
>Let's now say that I'm downloading a single very large file, from a very
>reliable and stable source and that I'm using the maximum 512kbits per
>second to get this file (a 'distro' or a ripped DVD - it makes no difference
>to this example.).
>
>Let's assume that I'm the only person logged on at my exchange for now.
>
>I'm maxing out my download and everything is fine. Now, someone else from
>the same exchange logs on to their own 512kbit line and starts to download
>another file from another very reliable and stable source.
>
>We've now got two download in progress - both are dedicated to pulling data
>from the sources as fast and consistently as they can.
>
>What are the factors involved in this:

In the absence of anybody else commenting (as far as I can see on
this server) I'll have a go at this...

>e.g.
>
>Will both customers be on the same 'pipe' from the same ISP.

Perhaps. If they are on the same contention, and the same
wholesaler and the same ISP then they might be. Many ISPs have more
than one 'fat-pipe' though.

>
>What if one is on 'pipe1' and the other is on LLU (another 'pipe'
>involved'?)

I can only speak for Easynet LLU - where there is a completely
different path from the exchange compared to someone using BTs
wholesale system. I suspect the other LLU providers will be the same
though.


>
>Is the 50:1 line, in reality, a (512kbit * some factor) line - so that
>neither download will realise that someone else is sharing the same 'pipe'?

The contention happens on the BT link to BT central. If 2 people
on the same exchange and contention are going full blast, but the
combined rate isn't above that that has been provisioned by BT from
the exchange to Central, then contention won't kick in.

>
>Will I end up with a max/2 download speed?

In the above case - unlikely.

>
>How do things change if the other downloader is a 2Mbit line - does this
>mean he's on a different circuit, so that we are not affected by each
>other - do we still share a common 'pipe'?

Depends again. If the 2Mbit line is on the same contention then it
will share the exchange to Central pipe. If not - not.

>
>I'm interested in actual technical info rather than marketing speak.
>
>Thanks for anyone that can answer this or point me to the right links.

There is a further possibility of speed reduction if the ISP
doesn't provision enough bandwidth from Central to themselves, but
that is a different problem.

The above I *believe* to be correct - but would welcome
corrections on detail.

Regards,
Harry.

On Thu, 12 May 2005 10:13:55 +0100, Harry Broomhall
<(E-Mail Removed)> wrote:

> There is a further possibility of speed reduction if the ISP
>doesn't provision enough bandwidth from Central to themselves, but
>that is a different problem.
>
> The above I *believe* to be correct - but would welcome
>corrections on detail.

small point, the exchange contention is between the exchange and the
ATM network or "cloud". The BT Central is the connection from the ATM
network to the ISP. The nominal "up to 50:1" etc occurs on the
exchange virtual path link, the Central can be more or less contended
at the ISPs choice.

Phil
--
Tiscali - dialup speeds at Broadband prices.
AOL - the unlimited ISP of choice for heavy downloaders.

On Wed, 11 May 2005 23:46:07 GMT, "Donald McTrevor" <(E-Mail Removed)>
wrote:

>And in reality he would share that with 1000 users?
>Ie 50 users share each 512 kbit (0.5Mbit) so 10Mbit is
>20 times that 20X50=1000
>>

seems reasonable, except BT don't actually run at 50:1 so its more
like 300 users.

>> >Will I end up with a max/2 download speed?
>
>What does max/2 mean?

maximum divided by two ie 50% or half the maximum speed.

Phil