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Upgrades?

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Upgrades?

Ive just migrated this week my service is the broadband plus package 2mb.
Everything is fine,but im still on my old adsl 500 and not the adsl 2000 I should be on.Ive agreed to pay ths extra 14.99 line regrade but there are no open tickets for it have they forgot?
9 REPLIES
Plusnet Staff
Plusnet Staff
Posts: 12,169
Thanks: 18
Fixes: 1
Registered: 04-04-2007

Upgrades?

Hi,

I've replied to your ticket saying what you need to do to get the regrade moving.
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Please explain/clarify Contention ratios and upgrades...

I have just upgraded my ADSL connection to 4Mbit line in the certain knowledge that my line is not actually capable of much more than 512kbits. I have done this becuase I am currently experiencing latency problems at peak times which is ruining my computer gaming experience and believe it to be related to the contention ratio. Here is my thinking.

Previously I had 512kbit with a contention ratio of 20:1. At peak times this could mean that my 512kbit connection becomes 512/20 or 25.6k - ie less than a dial up modem!! The new service is 4Mbits at a contention ratio of 30:1 which means that the new minimum should be 4096/30 = 130kbit - just over an ISDN2 line. I would like confirmation from Plusnet that my calculations are correct and that my new service will indeed deliver >=130kbits at all times.

I have purchased and ADSL 2 modem that should maximise my link between myself and the exchange but I'm not really worried about the maximum - when its quiet I have more than enough bandwidth to play my games, but with 3 people playing at the same time on the same connection the link is sometimes not fast enough. I would be more than happy with a 512kbit connection, its only the contention ratio that I don't like!!
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Upgrades?

What?

Your line is only capable of 512kbps but you've asked for a regrade to 4MbpsHuh

The line limits are based on the signal strenght and have nothing to do with contention etc... so you'll fail the regrade and will remain on 512.
Community Veteran
Posts: 5,877
Thanks: 1
Registered: 05-04-2007

Upgrades?

That's what the OP is saying although his line is only capable of 512k contention keeps kicking in making his connection really slow so if he goes onto the up to 4MB product he will supposedly have more bandwith when contented. Whether this will work or not I don't know!
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Upgrades?

Nope.

It won't work like that.

His line will not be upgraded as it will continually fail and drop sync etc.

And remember the odds of the other 30 users using all their share at the same time is quite low and so the contention won't always be a simple case of <MAX KBPS>/<MAX USERS> -- it will be <MAX KBPS>/<CURRENT USERS> and that will vary from second to second.
Community Veteran
Posts: 5,877
Thanks: 1
Registered: 05-04-2007

Upgrades?

I know the line won't be upgraded. But are you saying that even though the OP would be paying for a 4MB connection he the contention will still be worked out from 512k?
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This is what I am trying to say!!

Ok, as an engineer who has designed the chips in over 20 million ADSL modems and therefore know something about this, what I am asking for is what I should get!!!!!

There is a dedicated modem pair between my home router and the BT exchange. The datarate that is achieved between these modems depends on the quality of the line between the two. I have around 5km of line between myself and the exchange which results in about 60dB of attenuation and means the modems can get around 700kbits/sec downstream. That gets me into the DSLAM (Digital Subscriber line access multiplexor) at the exchange. BT then transfers my packets over their ATM network to Plusnet. This is where the contention ratio comes in - they oversubscribe the bandwidth on this link according to how much Plusnet pays for. If I pay plusnet for 4Mbits then I at 30:1 contention ratio then I should get >=130kbits/sec.

Anything less amounts to discrimination against people who are further away from the exchange. I want to pay extra for this service - surely BT/plusnet should be able to arrange to take my money? Or should I find a provider who will give me a 10:1 contention ratio and leave Plusnet?Huh
Community Gaffer
Community Gaffer
Posts: 12,803
Thanks: 635
Fixes: 62
Registered: 04-04-2007

Upgrades?

Hi there,

OK there are effectively 2 points of contention. At the exchange and across our network. BT only contend in two flavours at the exchange. 20:1 and 50:1. We have varying levels of contention across our network dependent on your package. It is commonly accepted that BT overprovide at the exchange so true 20:1/50:1 is rarely seen.

Castlefarm, I do not think that upgrading to the 4MB package will see a difference to your latency as the only change (assuming you remain at 20:1 at the exchange) is to the advertised contention at our side which is likely to be the same for the two accounts.

Regards,

Bob Pullen
Plusnet Products Team
If I've been helpful then please give thanks ⤵

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Upgrades?

We'll at the risk of getting into detailed semantics of how to set-up a PVC on a BT ATM switch, how can BT guarantee a 20:1 contention ratio if it does not know how much bandwidth is is being contended forHuh If the PVC is set up for 4Mbits at a contention ratio of 20:1 then the QOS inside the switch will automatically load balance based on these paremeters, sharing the bandwidth equitably (but not necessarily equally!).

Silly example - total actual backbone bandwidth 3Mbits, user 1 pays for 2Mbits, 4 other users @512kbits, total requested = 4Mbits - result is user 1 gets 1.5Mbits (ie 3/4), all the rest get 384k (also 3/4). I want to be USER 1!!

The corrolory is that if you are correct then nobody should sign up for anything other than the minimum service as the contention ratio is based on the lowest number - ie if one user pays for 512 and another for 2048, then the 512 user will get a better deal as his minimum is the same as the person who has paid more.

Or, ar you saying that BT dont want to sell me a service that the cant provide? If I cant get 4Mbits then they wont sell me the service period? Thats just stupid. I am happy with 512k max, I just dont want the minimum to be as bad as it is now and I'm willing to pay money for them to enable this.

Actually, Ironically the new service is less than my original service.... I will surf for alternatives..