Explanation of contention ratios please

I am a bit confused as to what contention ratios amount to. I know it is
mostly 50:1, but exactly what size of connection are these 50 sharing.
If you are a 512 connection then would there be 50 on this. I know that
most pipes are 155 but presumably this is just racked up on the former.

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Regards


David G
(remove r u n)

David G wrote:
> I am a bit confused as to what contention ratios amount to. I know it is
> mostly 50:1, but exactly what size of connection are these 50 sharing.
> If you are a 512 connection then would there be 50 on this. I know that
> most pipes are 155 but presumably this is just racked up on the former.

A useful primer is here:- http://www.aaisp.net.uk/aa/adsl/technical.html

"Hiram Hackenbacker" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> David G wrote:
>> I am a bit confused as to what contention ratios amount to. I know it is
>> mostly 50:1, but exactly what size of connection are these 50 sharing. If
>> you are a 512 connection then would there be 50 on this. I know that most
>> pipes are 155 but presumably this is just racked up on the former.
>
> A useful primer is here:- http://www.aaisp.net.uk/aa/adsl/technical.html

useful info Tks ( from a cable user )
--

Yddap
Remove guts to reply

On Fri, 19 Nov 2004 09:17:14 +0000, David G <notreallyhere@sure>
wrote:

>If you are a 512 connection then would there be 50 on this.

no, common misconception. If you are on 512 you have an exclusive 512
link to the exchange. Contention occurs after that on a bigger sized
connection shared by many users.

Beyond the exchange the capacity is:

Link capacity = No. of users * connection speed / actual contention

So there may be 300 512k users on a connection at an actual contention
rate of 15:1 (the 50:1 etc are maxima) so this becomes:

Link capacity = 300 * 512k / 15 = 10 Mbits/s

Where there are a lot of users sharing a big pipe contention isn't
often seen to have an effect. Where there are a few users on a small
pipe the probability of seeing it goes up - a datastream ISP may have
a 4M link into an exchange and sell services of 512k, 1M and 2M over
it. 2 of their 2M customers can fill it whereas in the above example
it needs 20 512k customers at full tilt to fill the 10M pipe.

Phil
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Phil Thompson <(E-Mail Removed)> wrote:

: So there may be 300 512k users on a connection at an actual contention
: rate of 15:1 (the 50:1 etc are maxima) so this becomes:

: Link capacity = 300 * 512k / 15 = 10 Mbits/s

: Where there are a lot of users sharing a big pipe contention isn't
: often seen to have an effect.

Of course BT operate, in reality, at nowhere near 50:1 at the moment and
several informed articles I have seen suggest the broadband service would
severely degrade if they ever went much over an operational ratio of
much higher than about 15:1. This, of course, also means that paying extra
for 20:1 contention does not often gain anything much at the present time.

Phil Thompson wrote:
> On Fri, 19 Nov 2004 09:17:14 +0000, David G <notreallyhere@sure>
> wrote:
>
>
>>If you are a 512 connection then would there be 50 on this.
>
>
> no, common misconception. If you are on 512 you have an exclusive 512
> link to the exchange. Contention occurs after that on a bigger sized
> connection shared by many users.
>
> Beyond the exchange the capacity is:
>
> Link capacity = No. of users * connection speed / actual contention
>
> So there may be 300 512k users on a connection at an actual contention
> rate of 15:1 (the 50:1 etc are maxima) so this becomes:
>
> Link capacity = 300 * 512k / 15 = 10 Mbits/s
>
> Where there are a lot of users sharing a big pipe contention isn't
> often seen to have an effect. Where there are a few users on a small
> pipe the probability of seeing it goes up - a datastream ISP may have
> a 4M link into an exchange and sell services of 512k, 1M and 2M over
> it. 2 of their 2M customers can fill it whereas in the above example
> it needs 20 512k customers at full tilt to fill the 10M pipe.
>
> Phil

Thanks All for the replies - got a better idea of it now

--
Regards


David G
(remove r u n)

On Fri, 19 Nov 2004 11:32:18 +0000 (UTC), Brian McIlwrath
<(E-Mail Removed)> wrote:
[snip]
>This, of course, also means that paying extra
>for 20:1 contention does not often gain anything much at the present time.

Many ISPs have "business" and "home" packages where the only
difference in specs is the CR.

So are you saying that the extra £20+ per month would be money wasted?
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On Fri, 19 Nov 2004 11:32:18 +0000 (UTC), Brian McIlwrath
<(E-Mail Removed)> wrote:

>an operational ratio of
>much higher than about 15:1. This, of course, also means that paying extra
>for 20:1 contention does not often gain anything much at the present time.

hence I used 15 in the example.

Of course the 20:1 accounts may be running at 10:1 or 5:1 for all we
know so there would still be an advantage (they aren't on the same
virtual circuits as the 50:1 accounts)

Phil
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