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MaxDSL and upload speeds

aeroalfie
Grafter
Posts: 400
Registered: 03-10-2007

MaxDSL and upload speeds

I’m not on maxDSL yet but looking at info on it why is the upload speed such a small increase ?
14 REPLIES
Community Veteran
Posts: 14,469
Registered: 30-07-2007

MaxDSL and upload speeds

Because ADSL uses a small frequency range to support the upload speed thus there is not that much above what is used noe for 256Kbs speeds to give you much higher upload speeds. IPStream max will support up to 448Kbs upload and IPstream max premier will support up to 832Kbs. the ADSL 1 spec only allows for a max of 1Mbs upload anyway.

Your line condition determins how much of the frequency band ADSL can use and affects both your max upload speed and your max download speed within the ADSL1 spec. The better your line quality the more frequencies that can be used and thus faster transfers can be achieved.
MrToast
Grafter
Posts: 550
Registered: 31-07-2007

MaxDSL and upload speeds

Quote
the ADSL 1 spec only allows for a max of 1Mbs upload anyway.


Hmmm... does that mean that the contention ratio on BT's network for upload is different to that for download? Most Telco connectivity is Bi-Directional.

And why wouldn't they make the full capability of ADSL 1 available anyway now that individual line conditions can be assesed automatically under MaxDSL.
Community Veteran
Posts: 26,345
Thanks: 600
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Registered: 10-04-2007

MaxDSL and upload speeds

It's nothing to do with contention ratios.

ADSL stands for Asynchronous Digital Subscriber Lines. A range of frequencies are assigned to upload and a separate range to download. Because most internet activity is downloading more of the frequencies are assigned to downloading.

It would probably be possible to give the full upload speed, but you can't have something for nothing, so it would be at the expense of download speed.
jelv (a.k.a Spoon Whittler)
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James
Grafter
Posts: 21,036
Registered: 04-04-2007

MaxDSL and upload speeds

It's Assymmetric Digital Subscriber Line.

Sorry Smiley
Community Veteran
Posts: 38,215
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Registered: 15-06-2007

MaxDSL and upload speeds

Given the above facts can someone explain to a simple soul how the new system will set the upload speeds in relation to download speeds. i.e. will it max out the upload speed at 448kb/s and then use whatever is left for the download speeds or could the download speed affect the maximum upload speed.
Community Veteran
Posts: 26,345
Thanks: 600
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Registered: 10-04-2007

MaxDSL and upload speeds

Shockedops: Of course it is. At least I got the rest of the description right.

Thanks for the correction James
jelv (a.k.a Spoon Whittler)
   Why I have left Plusnet (warning: long post!)   
Broadband: Andrews & Arnold Home::1 (FTTC 80/20)
Line rental: Pulse 8 Home Line Rental (£13/month)
Mobile: iD mobile (£4/month)
Community Veteran
Posts: 14,469
Registered: 30-07-2007

MaxDSL and upload speeds

Download has a certain frequency range allocated for it's data and that frequency range is split up into bands.
Upload has a separate and different frequency range allocated for it's data, also split into bands.

Within each frequency range the exchange will try and get the best reliable speed it can by using as much of the allocated frequencies as it can. Some lines will have dead areas in the frequency ranges which cannot be used. The more dead areas there are, the lower the number of bands available and thus the slower the maximum achievable speed is as there are less frequency bands to use for data.

The current technology will not try to max out either upload or download, it will try to get the best within each frequency group.
MrToast
Grafter
Posts: 550
Registered: 31-07-2007

MaxDSL and upload speeds

Yes I know what ADSL means.....

What i was trying to ask, incase anyone knows, is that given the asymetric nature of the connection between the DSLAM and the customer does that mean that the contention ratio on the network becomes Asymetric also.

I pointed out that Telco networks tend to be Bi-directional. If a central Pipe is 155 or 622Mbps or what ever would it be the same capacity in each direction? If so the contention ratio the customers get will be lower for upload (because their upload bandwidths are less) compared to the download contention.

Unless..... particular steps have been taken to equalise the upload / download ratios....

Sorry if i wasn't clear first time.
N/A

MaxDSL and upload speeds

The theoretical upload / download speeds are NOT a function of the contention ratio on the exchange or any other path. The upload / download speeds are a function of the frequency range used by the ADSL system. For downloads the frequency range is that much wider (hence 'broadband' if you take the proper comm's definition of broadband) than the upload frequency bands so you get the difference between upload/download capacity.

Where the contention ratio kicks in is on the exchange and that has the effect of reducing the actual throughput - however regardless of contention the line will still sync at the approriate upload/download speeds rather than the contended actual throughput.
Plusnet Staff
Plusnet Staff
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Registered: 04-04-2007

MaxDSL and upload speeds

Quote
What i was trying to ask, incase anyone knows, is that given the asymetric nature of the connection between the DSLAM and the customer does that mean that the contention ratio on the network becomes Asymetric also.


A 622Mbps pipe can actually carry 933Mbps of data in both directions combined. This is usually split up as 622 down and 311 up, although you can change it and increase the upload by decreasing the download (for example 600 down and 333 up). You can't though increase the download any higher than 622.

I don't know how it works going back across the ATM network, I would suspect that the network is pretty much symmetric across the rest of BT's network, although that would be a guess just because they have to send traffic around the country from one RAS to another and RAS's will differ depending on the ISP. For example, on PlusNet a customer in Manchester may see traffic go from their exchange to the Manchester RAS down to a London RAS to get to Telehouse, whereas someone on Zen in London would see the traffic go the other way, London RAS to Manchester RAS to Zen.
MrToast
Grafter
Posts: 550
Registered: 31-07-2007

MaxDSL and upload speeds

Thanks Dave,

That sheds some light on it. I hadn't thought about alternative RAS's....

Interesting about the central pipes though...
Plusnet Staff
Plusnet Staff
Posts: 12,169
Thanks: 18
Fixes: 1
Registered: 04-04-2007

MaxDSL and upload speeds

There's probably more traffic going north to south than south to north, but how it's all setup and what capacity is where is probably something only BT know.
N/A

MaxDSL and upload speeds

Quote
It's Assymmetric Digital Subscriber Line.

Sorry Smiley


Think you'll find it's Asymmetric
sputty
Grafter
Posts: 43
Registered: 02-09-2007

MaxDSL and upload speeds

An interesting presentation from BT all about how it all works, if you have the time to go through it all that is.

The Network Story

Its a long presentation and starts off very basic , but will give a lot of information "eventually"

Smiley