Many users are currently asking how they can find out if they will be able to get higher speeds.
Probably the easiest way is to check your phone number with the BTwholesale checker to see what speed that says you will get.
However, there have been instances whereby the BT database has incorrect information and as such you may not be able to automatically get a speed upgrade.

One of the more accurate ways of finding out is asking your ISP to perform a WOOSH test which will advise your ISP of your line "Loop Loss" and SNR Margin. Most ISPs are reluctant to perform these tests due to the time element involved, unless its for fault diagnosis.

However you should be able to get line stats from your modem / router yourself.
The figures you are looking for are Attenuation and the SNR (noise) Margin.
Both of these figures are measured in decibels (dB).

Line Attenuation.

Line attention is in relation to the "loop loss" on your line.
The further you are away from the exchange the higher your attenuation figure will be as the signal loss increases.
The lower your attenuation figure the more chance you have of getting the faster speeds.

SNR (Signal to Noise Ratio).

The SNR margin can only be measured from your own property and therefore to be measured correctly may need an engineer visit to check this figure from the BT test socket behind your master phone socket. Your SNR Margin can fluctuate on a day to day basis and may vary depending upon local equipment, conditions and interference.
An upgrade in speed often causes the SNR to decrease by up to 5 dB. The higher your SNR figure then the better your line quality and therefore a higher chance of getting faster speeds.
It is very important to note that SNR plays much more importance in maxdsl than it did on the traditional adsl product.

Line Length.

Ideally your line length should be below 3.5km from the exchange to get a fixed rate 2Mb connection and 6km for a 1Mb connection.*

At the present time the general public has no way of checking themselves this figure. However, you may be able to get a rough indication by using the adsl checker.

Please note that it measures your distance between your home and the exchange "as the crow flies" and due to cable routing your line length in reality will be longer depending upon BT's routing.

*The new reach limits came into effect on the 6th of September 2004. Prior to this date the limits were 6km for a rate adaptive product (512k) and 3km for a fixed product (1 & 2Mb).

The Results.

When determining what speed you can get the following figures may be used as a guide.
Remember you must use the downstream figures. :-

Downstream Attenuation for Fixed Rate Lines.

0-42 dB - 2Mbps (strictly adhered to wef Aug 2005)
43-60 dB - 1Mbps
> 60 dB - 512kbps

If you already have adsl enabled you may be able to add an extra couple of dB on those figures e.g. 44 dB would be the limit for a fixed 2Mb line. However, since Aug 2005 BT have adhered to the rules more due to the large number of recently failed 2Mb upgrades that have had to be regraded down to 1Mb.

There is a supposed soft-cap of about 70dB, but BTw wll try connect anythng up to 75dB attenuaton

Downstream SNR Margin

Should be at least 10 dB to get adsl - ideally above 12dB to get traditional fixed adsl.
Anything less than this will see frequent disconnections and other problems.
Maxdsl works slightly differently and your router will try to sync at the highest speed it can whilst maintaining a safe SNR Margin. The default is 6dB but more info on my max dsl page.

As previously stated these figures should be used as a guideline as it is possible to have a very good SNR Margin but poor attenuation figure and vice versa.

 

Getting your line stats.

Most routers and modems will show your line stats.
Ive compiled a list of how to get your line stats from the most common modems and routers.

An explanation of SNR and SNR Margin *

The SNR Margin is not the same as the Signal to Noise Ratio (SNR), although it is related.

The SNR is the signal-to-noise ratio. It is the ratio between the strength of the signal and the background noise on the line and is universally expressed as a logarithmic ratio (decibels or dB).
For a given line the SNR remains essentially fixed whatever the speed you are running.

ADSL routers and modems actually report the SNR Margin, and the term used to describe this varies but is generally “SNR Margin”, “Noise Margin”, “Margin”, “Receive Margin”.

The SNR Margin is the difference between the actual SNR and the SNR required to run at a given speed.
For example, if you need 20dB of SNR to run at 512Kbps, and the actual line SNR is 45dB, then the SNR Margin is 25dB.

The main reason why SNR margins fall as the line speed increases is that the required SNR increases.
For example, if increasing the speed from 512Kbps to 2MBps raises the required SNR from 20db to 30dB then the margin left will fall from 25dB to 15dB (as 45dB-30dB = 15dB.)
The one refinement is that if it is necessary for a faster speed to use some higher frequencies then these will have inherently lower SNRs and that will also contribute to the reduced SNR margin somewhat.

The SNR Margin is there to absorb fluctuations in interference on the line, and therefore to keep the service reliable. The figure of 6dB is normally accepted as enough headroom to make the link reliable, but some lines need more - 10dB is often accepted as a safer target.

Note that the target figures in the list are a reasonable summary, but it is the "SNR Margin" that is being talked about, not the "SNR". Despite this, it also does not invalidate the point that the most important factor on the reliability of a line at a given speed is the SNR Margin.
Also, as neither the SNR or SNR Margin can be established until a line is enabled (or validated with special test gear), then the estimated attenuation has to be used to come up with a viable speed. Once a line is enabled and working, it is possible - at least in theory - to gather information about the actual SNR and SNR Margin and use that to work out the actual speed the line will be able to sustain. This is essentially what will happen with the MaxDSL launch towards the end of the year.

* The above explanation has been slightly adapted from an original post made by Steve J (nopr0700) on adsl guide forums. - Due to the fact that forum posts are often archived, I have reproduced his information on this page. Thanks Steve.

Improving your Line Stats.

Many people have asked if there's anything that can be done to improve your line stats. There isnt much you can do about your attenuation, because that is dependant upon line length, however there are a few things that may help improve your SNR Margin.

As the days of MaxDSL draw nearer, the speed of which your line will sync at will be more dependant upon your SNR Margin than your attentuation figure.

63.5 dB Attenuation??

The reason some routers/modems will report 63.5 dB as the maximum attenuation isnt actually a bug. In fact its from the G.992.1 standard which quotes "The attenuation ranges from 0 to 63.5 dB with 0.5 dB steps."
As such many firmware versions have taken this literally and only go up to 63.5dB when it is possible to have a higher attentuation figure than this.

 

My own figures:-

Which one would you believe?.. bearing in mind I can look out of my window and see the exchange.
All these tests were done from the same phone socket
- although it doesnt make any difference from the main to extension.

On 2Mb (SAR 110) Local Line Atten.: 21.5 dB Remote Line Atten.: 7.0 dB Local SNR Margin: 31.0 dB Remote SNR Margin: 26.0 dB	On 1 Mb (SAR 110) Local Line Atten.: 21.5 dB Remote Line Atten.: 7.0 dB Local SNR Margin: 35.0 dB Remote SNR Margin: 26.0 dB
From a Netgear DG834G Connection Speed 2272 kbps 288 kbps Line Attenuation Down:    12 db Line Attenuation Upstream:   4 db Noise Margin Down:      31 db Noise Margin Upstream:  29 db	From Woosh (SAR 110) Circuit Information: Circuit In Sync Upstream xDSL Link Info : Loop Loss 6 dB Cell Count 634759003 Downstream xDSL Link Info : Loop Loss 21 dB Cell Count -1759228216
From Voyager 2100 Down Up       SNR (dB): 30.5 27.0 Attn(dB): 7.0 7.0 Pwr(dBm): 15.0 11.9 Max(Kbps): 10624 1144 Rate (Kbps): 2272 288	From Woosh (V2100) 8-8-05 xDSL Status Check OK Circuit Information Circuit In Sync Upstream xDSL Link Info Loop Loss 6 dB Cell Count 691654368 Downstream xDSL Link Info Loop Loss 7 dB Cell Count -1373046627
From SAR 110 (with firmware VIK-2.1.040311a) Local Tx Power: 11.95 dB Remote Tx Power: 17.55 dB Local Line Atten.: 9.5 dB Remote Line Atten.: 7.0 dB Local SNR Margin: 30.5 dB Remote SNR Margin: 26.0 dB	WOOSH test (SAR110) Upstream xDSL Link Info Loop Loss 6 dB Margin 19 dB Errored Seconds 0 HEC Errors 0 Cell Count 589949220 Speed 448 k Downstream xDSL Link Info Loop Loss 9 dB Margin 10 dB Errored Seconds 0 HEC Errors 0 Cell Count 2013098949 Speed 8128 k
From SAR 110 25/04/06 Local Tx Power: 11.95 dB Remote Tx Power: 17.69 dB Local Line Atten.: 9.5 dB Remote Line Atten.: 7.0 dB Local SNR Margin: 9.0 dB Remote SNR Margin: 20.0 dB