Contention ratio

I'm investigating going from dial-up to ADSL with my current ISP (mainly to
keep the same email address).

This month's PC Pro article "The Great Broadband Con" for Fixed-line
broadband notes "...the level of contention...is a major source of the
problem...".

When I asked my ISP what their contention ratio is, they replied:

Contention ratios no longer apply to ADSL as of March 2006, BT have now
declared performance thresholds.

http://forum.zensupport.co.uk/7331/ShowThread.aspx#7331

So is contention ratio an issue or not?

TIA.

--
Jeff
(cut "thetape" to reply)

"Jeff Layman" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I'm investigating going from dial-up to ADSL with my current ISP (mainly
> to keep the same email address).
>
> This month's PC Pro article "The Great Broadband Con" for Fixed-line
> broadband notes "...the level of contention...is a major source of the
> problem...".
>
> When I asked my ISP what their contention ratio is, they replied:
>
> Contention ratios no longer apply to ADSL as of March 2006, BT have now
> declared performance thresholds.
>
> http://forum.zensupport.co.uk/7331/ShowThread.aspx#7331
>
> So is contention ratio an issue or not?
>
> TIA.

Yes, of course it is. It may be called by a different name now, but unless
we all get our own dedicated pipes we still have to share with others, and
that's contention. If you're the only person using the bandwidth at any
particulr time then you'll zip through like a hot knife through butter, but
the more people join you the slower it'll get.

Jeff Layman wrote:

> I'm investigating going from dial-up to ADSL with my current ISP

Which one ?

> (mainly to keep the same email address).

The very worst possible reason. Even if you move, a decent ISP will keep that
email account open and you'll be able to access it from your new connection. I
have several I've acquired that way. If it closes the email account, that's
probably not an ISP you should consider staying with anyway.


> This month's PC Pro article "The Great Broadband Con" for Fixed-line
> broadband notes "...the level of contention...is a major source of the
> problem...".
>
> When I asked my ISP what their contention ratio is, they replied:
>
> Contention ratios no longer apply to ADSL as of March 2006, BT have now
> declared performance thresholds.
>
> http://forum.zensupport.co.uk/7331/ShowThread.aspx#7331
>
> So is contention ratio an issue or not?

Contention generally is an issue but the contention ratio at the BT exchange
isn't any more AIUI. Most ISPs have plenty of contention ( i.e. lack of adequate
capacity ) on their own network though.

Generally you'll find the worst performers are the largest ISPs and especially
those with TV adverts.

Graham

Eeyore wrote:
> Most ISPs have plenty of contention ( i.e. lack of adequate
> capacity ) on their own network though.

What?

ADSL is designed as a contended service, it is nothing to do with
"adequate capacity". If you want an uncontended service, they are
available, but they are not <£30/month.

Paul Cupis wrote:

> Eeyore wrote:
> > Most ISPs have plenty of contention ( i.e. lack of adequate
> > capacity ) on their own network though.
>
> What?
>
> ADSL is designed as a contended service, it is nothing to do with
> "adequate capacity".

Contention is ALL ABOUT CAPACITY.

> If you want an uncontended service, they are
> available, but they are not <£30/month.

An uncontended service (per the BT meaning of the word) could still have
contention over the ISP's network for example. In practice it's unlikely to
suffer that but only because only decent ISPs who don't oversubscribe tend to
offer these.

Between your PC and a website or any server you can have no less than 4 main
sources of contention. At the equipment rack in the exchange, over the ISP's
network, over the 'net' as a whole and finally on the target host.

Graham

Eeyore wrote:

> Between your PC and a website or any server you can have no less than 4 main
> sources of contention. At the equipment rack in the exchange, over the ISP's
> network, over the 'net' as a whole and finally on the target host.

This man speaks the truth. In my experience exchange contention has been
a much smaller factor in experienced throughput than people think. The
ISP's backhaul peering and transit is the source of performance problems
in a much larger number of cases.

BT's chunk of the ADSL network is actually very good at delivering
throughput to meet their 8Mbps claims, even with expected contention
taken into account. ISPs are struggling to balance the costs of transit
against a market with ever narrowing profit margins, meaning a lot of
people won't see those speeds even with perfect connectivity to and
beyond the exchange.

That's not to say it isn't possible and a few ISPs (Be and Sky come to
mind) can deliver end speeds far beyond 8Mbps at quieter times of the day.

--
Jay L. T. Cornwall, http://www.esuna.co.uk/~jay/
PhD Student
Imperial College London

In article <f7stj1$ia7$1$(E-Mail Removed)>, Jay L. T. Cornwall
<(E-Mail Removed)> wrote:

> Eeyore wrote:
>
> > Between your PC and a website or any server you can have no less than 4 main
> > sources of contention. At the equipment rack in the exchange, over the ISP's
> > network, over the 'net' as a whole and finally on the target host.
>
> This man speaks the truth. In my experience exchange contention has been
> a much smaller factor in experienced throughput than people think. The
> ISP's backhaul peering and transit is the source of performance problems
> in a much larger number of cases.

This is consistent with my own experience.

For many months months on MaxADSL with Nildram I experienced very low
speeds most of the time. Occasionally it jumped up to 5 Mbps but most
of the time it was around 1 Mbps and sometimes for hours at a time it
was below 0.5 Mbps. Of course I complained to Nildram, jumped through
all the hoops and did all their tests but in the end they just blamed
it on congestion at my exchange.

Information I obtained about my exchange indicated to me that it was
highly unlikely that congestion at my exchange was bad enough to cause
such a huge decrease in speed. So I decided to try another ISP. If the
problem was with my exchange then I'd probably still have the problem
with the new ISP. However, this was £10 per month cheaper so even if
the problem remained I'd still have been better off financially.

So, on 4th June this year I migrated to the new ISP and since then I
get speeds over 5 Mbps almost all the time. The lowest speed I
recorded was just over 3 Mbps during the early part of the ISP off-peak
time. Since migrating on 4th June I've done 80 tests on speedtest.net
and got these results:

Fastest Download: 6212 kb/s
Fastest Upload: 364 kb/s
Average Download: 5789 kb/s
Average Upload: 363 kb/s

Now of course it is possible that the exchange congestion disappeared
on exactly the same afternoon that I migrated, but that would seem to
be a rather big coincidence. Personally I think it more likely that
Nildram was the source of the speed problems and that they were
mistaken (or lying) when they blamed it on my exchange.

Kit

Eeyore wrote:
> Paul Cupis wrote:
>> Eeyore wrote:
>>> Most ISPs have plenty of contention ( i.e. lack of adequate
>>> capacity ) on their own network though.
>> What?
>>
>> ADSL is designed as a contended service, it is nothing to do with
>> "adequate capacity".
>
> Contention is ALL ABOUT CAPACITY.

I quoted "adequate capacity". Contention on a contended service does not
suggest a "lack of adequate capacity" at all - this is the design of
the product.

>> If you want an uncontended service, they are
>> available, but they are not <£30/month.
>
> An uncontended service (per the BT meaning of the word) could still have
> contention over the ISP's network for example. In practice it's unlikely to
> suffer that but only because only decent ISPs who don't oversubscribe tend to
> offer these.

Most ISPs do not have contention over their network, it is usually at
the point of interconnect with their DSL wholesaler. It is trivially
easy and cheaper to have an uncontended network for the ISP, but the
capacity to interconnect with BTwholesale or another wholesaler is
expensive.

On Sat, 21 Jul 2007 13:18:41 +0100, "Jay L. T. Cornwall"
<(E-Mail Removed)> wrote:

>BT's chunk of the ADSL network is actually very good at delivering
>throughput to meet their 8Mbps claims, even with expected contention
>taken into account. ISPs are struggling to balance the costs of transit
>against a market with ever narrowing profit margins, meaning a lot of
>people won't see those speeds even with perfect connectivity to and
>beyond the exchange.
>
>That's not to say it isn't possible and a few ISPs (Be and Sky come to
>mind) can deliver end speeds far beyond 8Mbps at quieter times of the day.

Be and Sky* don't pay BT for centrals. Therein lies the salient
difference. If you think otherwise then you know not of what you speak
;-)

PS - I think you'll find that even BT acknowledge that the vast
majority of exchanges will NOT provide an 8Mbps service on ADSLMax at
peak times.

*Sky obviously do pay for centrals for exchanges they haven't
unbundled but the price to the end-user varies too.

In article <(E-Mail Removed)>, Mr Adams
<(E-Mail Removed)> wrote:

> On Sat, 21 Jul 2007 13:18:41 +0100, "Jay L. T. Cornwall"
> <(E-Mail Removed)> wrote:
>
> >BT's chunk of the ADSL network is actually very good at delivering
> >throughput to meet their 8Mbps claims, even with expected contention
> >taken into account. ISPs are struggling to balance the costs of transit
> >against a market with ever narrowing profit margins, meaning a lot of
> >people won't see those speeds even with perfect connectivity to and
> >beyond the exchange.
> >
> >That's not to say it isn't possible and a few ISPs (Be and Sky come to
> >mind) can deliver end speeds far beyond 8Mbps at quieter times of the day.
>
> Be and Sky* don't pay BT for centrals. Therein lies the salient
> difference. If you think otherwise then you know not of what you speak
> ;-)
>
> PS - I think you'll find that even BT acknowledge that the vast
> majority of exchanges will NOT provide an 8Mbps service on ADSLMax at
> peak times.

Yes, but slow speeds are not always caused by congested exchanges.
Keeping everything else the same and migrating to another ISP
dramatically increased speeds for me. (See my post on this subject
earlier today.)

It's easy for a bad ISP to blame slow speeds on your exchange when in
fact the slow speeds are because they are not buying enough capacity,
centrals, or whatever. They simply want to increase profits by
decreasing expenditure and relying on the fact that most of their
customers will not be bothered to migrate. The ISP customer service
people tell you that the problem is with your exchange so that
migrating to another ISP won't increase your speeds.

Of course not all ISPs are bad, just as not all builders are cowboys
and not all used car salesmen want to swindle you. Some ISPs started
off great (e.g. Nildram several years ago) and then in recent years
went downhill. The important thing is to shop around and look for ISPs
with a good reputation now.

One thing to beware of is an ISP is taken over - there is then a high
probability that the buyer will want to recoup the purchase price by
making more short-term profit. Investing in increased capacity and
other services does not increase short-term profits.

Kit