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Contention Ratio's

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Contention Ratio's

I am on the Standard home ADSL (512/256) package which I believe has a contention ratio of 50:1.

I have heard contention ratios quoted as being different for ADSL than other connections e.g. cable, but I still don't know exactly what it means.

Does it mean that if the other 49 people who I am contended with are all surfing the net I will share my 512kb/s with them all! leaving everyone with 10kbps at REALLY busy times (Surely not!)

Is it linked to the exchange in any way i.e. am I contended with people only on my exchange?

Is it to do with the TOTAL number of people using the plus net service at any one time?


I only ask all these questions, because whenever (that is absolutely anytime, 6pm, 4am, 9am, whenever!) I can ALWAYS download at 60KB/s+ continuously, that’s about 480kbps, which is about full speed when overheads and the like are taken into account!

Are 98% of ADSL customer’s just not using thier connections at all! (Hard to believe) or have I got the contention ratio logic all wrong?

Any comments from people who actually know anything about this would be greatly appreciated.

Maybe I am just lucky (I’d better keep quite, Doh! too late)

Stuart
6 REPLIES
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RE: Contention Ratio's

Danm messed up character set,

for ’ please read '

:deadhead:

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RE: Contention Ratio's

> Danm messed up character set,
>
> for ’ please read '
>
> :deadhead:
>
>

Have you taken a look at http://www.adslguide.org.uk/howitworks/contention.asp

Cheers
Dave B
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RE: Contention Ratio's

Thanks Dave,

the bit that really should concern people is this extract:
"If you take the worst case scenario for the home user then that means you're sharing your 500kbs with 49 other people. If you are all downloading at the same time then you'll get 10kbs - about a quarter of the speed of a normal dial-up analogue modem."

However it doesn't explain WHO I am contended with and at what stage the contention occurs?

Am i right in thinking if i am using 60KB/s then 49 other people are not using anything!

Are those 49 people always the same people?

What i really want to know is: Right now my connection is A1 (thanks PlusNET), but with ADSL getting cheaper will more people in my area with ADSL reduce my performance as with cable?

Any ideas...Plus NET?


> > Danm messed up character set,
> >
> > for ’ please read '
> >
> > :deadhead:
> >
> >
>
> Have you taken a look at http://www.adslguide.org.uk/howitworks/contention.asp
>
> Cheers
> Dave B

benoh
Grafter
Posts: 272
Registered: 24-08-2007

RE: Contention Ratio's

> Thanks Dave,
>
> the bit that really should concern people is this extract:
> "If you take the worst case scenario for the home user then that means you're sharing your 500kbs with 49 other people. If you are all downloading at the same time then you'll get 10kbs - about a quarter of the speed of a normal dial-up analogue modem."
>
> However it doesn't explain WHO I am contended with and at what stage the contention occurs?
>
> Am i right in thinking if i am using 60KB/s then 49 other people are not using anything!
>
> Are those 49 people always the same people?
>
> What i really want to know is: Right now my connection is A1 (thanks PlusNET), but with ADSL getting cheaper will more people in my area with ADSL reduce my performance as with cable?
>
> Any ideas...Plus NET?
>
>

Hi,
Contention on DSL *should* take place in the exchange or on the backhaul to BTs ATM network.

This means if it happens you would be contented with people on your own exchange and I believe it is only between 3 ISP's, i.e, 50 users of Plusnet, nildram and openworld (example) in total would cause contention at the exchange. At the moment it is known that contention is not occouring in the exchanges and no one is really sure what will happen if it ever does.

50:1 is high, and the likelyhood is that BT would change this to something like 20:1 if it ever happened or simply upgrade capacity as needed to keep it with no contention (this isn't the same as 1:1 as contention could ocour if busy still)

Contention can also occour in the links from BT into your ISPs network, we currently have 5x155Mb links from BT. These run just over 50% capacity (See http://portal.plus.net/supportpages.html?D10diomB6dQ%3D for realtime graphs) and we have 6 more on order for the coming months.

The last place where contention could occour is in the "external" bandwidth available to the entire userbase of the ISP toing out onto the internet. We currently have 3x622Mb, 2x100Mb and several "private" peering arrangements so theres plenty to play with Smiley

Then its down to the internet which is ALWAYS the slowest point. Remember that you can only go as fast as the slowest link!

http://portal.plus.net/general/network_ADSL.html Has some info on how we manage our network.

Ben O'Hara
Network Support Engineer
Plusnet Technologies
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RE: Contention Ratio's

As u understand it (as it was once explained to me), is that the 50 users share a 10Mb line to the ISP, through your exchange. This means that if everyone was downloading at full speed then you should still get a speed of around 20-25KB/sec (by my caluclations Smiley). This means that if your getting a speed lower than this, there is something up.

Because there is hardly ever that amount of users on at the same time then we get high speeds

Hope this helps.

Dave
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RE: Contention Ratio's

Thanks everyone for your replies Smiley

Dave, Your reply sounds like the "Sensible & Simple" one I was hopeing for!

Can anyone at plusnet confirm this is the case?

ADSL guide seems to suggest that it is 500kb that is shared between users:
http://www.adslguide.org.uk/howitworks/contention.asp

Damn I'm confused :confused:

Anyway, I don't suppose it really matters as long as my speeds stay high !