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ADSL Contention 50:1 - need more understanding!

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ADSL Contention 50:1 - need more understanding!

Ok, I already know that the 50:1 ratio means I share my bandwidth with up to 49 other users at the same time at any given time.

Is this a ratio of ADSL connections to local BT exchange regardless of ISP? So if I live in an area where i suspect there are less than 30 ADSL users, I should usually have plenty of available bandwidth?
6 REPLIES
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RE: ADSL Contention 50:1 - need more understanding!

Hi Spencer,

You are correct with your first statement.

As to the second, afaik, for each 50 users on the exchange, a certain amount of bandwidth is allocated to that pipe. So technically yes, if there are less that 50 users on that particular connection then you theoretically would have more bandwidth available for download.

I believe this to be the way it works, if I am wrong, then someone please correct me Smiley

Best Regards
Chris

> Ok, I already know that the 50:1 ratio means I share my bandwidth with up to 49 other users at the same time at any given time.
>
> Is this a ratio of ADSL connections to local BT exchange regardless of ISP? So if I live in an area where i suspect there are less than 30 ADSL users, I should usually have plenty of available bandwidth?

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RE: ADSL Contention 50:1 - need more understanding!

Statistical multiplexing is a bit more complicated than that.

and there are some statistical efficiencies that come in, on larger pipes,
obviously, if the pipe is 100% loaded, it doesn't matter how big it is, really.

So I would consider smaller pipes to be more rapidly fluctuating in load, (like waves on the shore, where as the larger pipes, would fluctuate like the big rolling waves, out in the ocean.)

ok, best analogy I could come up with on short notice., I think this makes us ADSL users, water droplets, and 56 modem users into water molecules.

and just like the real sea.. sometime, when you go to the beach. the tide is out.!

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
However, this still hasn't answered the original question, which was where does the contention occur?

As previous CS postings suggested that BT feed an uncontended line to plusnet. (anyone else read that??)
CS cited this, as the main reason for the recent troubles., and also why they need to buy in big capacity lines.

If this is the case, then only plusnet users are contended with other plusnet users.

If, the contention occurs on the exchange, then I guess we are being contending with other ISPs, which hints at the suggestion that no matter which ISP you choose, your bandwidth will be determined by who else is running on your exchange, and not by which ISP you choose, (interesting thought)

As I don;t think it's feasible, for users to be separated out, per isp, at every exchange, then logically the separation must occur at a central point,
ie, telehouse..
Then plusnet buy a pipe hooked into telehouse where only their adsl users get routed through.

How close is this, for a guess?
Anyone have a more definitve answer?


Also, there is the outstanding question over where in the system the business users, are multiplexed with the residential users.

Do plusnet have a separate pipe, for each service class? or, at some point are business and residentials, multiplexed before that.?
ie Does any spare capacity on either portion get used to supplement the other?


lots of Qs to follow... Wink

















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RE: ADSL Contention 50:1 - need more understanding!

So the question remains, am I sharing the bandwidth with 49 other Plusnet users on ISP network OR am I sharing the bandwidth with 49 other ADSL users with activated lines to ADSL enabled local BT exchange?Huh
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RE: ADSL Contention 50:1 - need more understanding!

Lets put this simpler..

You connect directly to the exchange(like anyone on any isp), and the outpipe from the exchange, goes off to telehouse

all the exchanges feed into telehouse, and your isp, buys a pipe, from there.
It's the size of that pipe, which determines your isps capacity and consequently level of service.

Due to contradicting information posted, it's not clear where the contention in introduced.?
Is the contention done, on the upline from the exchange,
ie, the exchange pipe = 512Kbs * number of subscribers /50(contention)


or is that exchange line a full capacity pipe, and contention handled, after the data arrives at telehouse, or indeed, after reaching the plusnet network?

ie, at the point of contention, the fatter link must be flow controlled, does this happen at telehouse, or at the local exchange.?

hmm wonder if anyone understands this....



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

RE: ADSL Contention 50:1 - need more understanding!

> Lets put this simpler..
>
> You connect directly to the exchange(like anyone on any isp), and the outpipe from the exchange, goes off to telehouse
>
> all the exchanges feed into telehouse, and your isp, buys a pipe, from there.
> It's the size of that pipe, which determines your isps capacity and consequently level of service.
>
> Due to contradicting information posted, it's not clear where the contention in introduced.?
> Is the contention done, on the upline from the exchange,
> ie, the exchange pipe = 512Kbs * number of subscribers /50(contention)
>
>
> or is that exchange line a full capacity pipe, and contention handled, after the data arrives at telehouse, or indeed, after reaching the plusnet network?
>
> ie, at the point of contention, the fatter link must be flow controlled, does this happen at telehouse, or at the local exchange.?
>
> hmm wonder if anyone understands this....
>
>
>
>

http://www.adslguide.org.uk/howitworks/default.asp

Glad to see its all working nicely again.

Ben O'Hara

Network Support analyst
Plusnet Technologies Ltd.
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RE: ADSL Contention 50:1 - need more understanding!

> http://www.adslguide.org.uk/howitworks/default.asp
>
> Glad to see its all working nicely again.
>
> Ben O'Hara
>
> Network Support analyst
> Plusnet Technologies Ltd.
>

According to that site, you ARE contended by ISP's Home Gateway and not by the local exchange.

But contention will be done by local exchange when ADSL users reaches a certain amount.