No, they are BT guesstimates
real figures attainable from some routers, Signal to noise and attenuation.
my Att is 58.5 - just under the max possible for 1 meg
my S2N is 14.5, not quite so important
fyi, from thinkbroadband.com
* Line Length
(They need to know how far you are from the exchange), you must be within ~3.5km to pass for the 2Mbps product, and within approximately 6km for the 1Mbps ADSL products. There is no set limit for a 0.5Mbps service, all but 0.2% of lines should support a 0.5Mbps service.NB: This is related to the length of the line rather than the physical distance from the exchange.
* Line Loss
(They need to ensure your line has suitable quality for ADSL), You need a line loss of no more than 43db for the 2Mbps product, 60dB for 1Mbps product. This test is normally a paper exercise based around the records for your line and area, if a border line figure appears they may test it out in the street. No limit exists for 0.5Mbps services, if you are connected to an enabled exchange your line will be enabled and if it does not work an engineer visit will be arranged to try and get you a service.
Before 6th September 2004, the limits were 41dB on both 1Mbps & 2Mbps products, and 60dB for 0.5Mbps. Additionally before 24th September 2003, the 512kbps line loss limit was 55dB.
* Capacitance
(Again, this is to establish line quality), to pass, this should be below 160nF - for RADSL the figure is believed to be 300nF (nF is nano-farods).
* APTS
This test uses special software on the engineers hardware to talk to the DSLAM and measure the attenuation across the actual line. The limits using this kit are 43dB for a 2Mbps service, and 60dB for the 1Mbps service. Currently this is the definitive test, with 0.5Mbps it is a case of so long as your modem will work you can have the service.
* Woosh Attentuation Test
The woosh test is actual a whole suite of tests, the attenuation measurements are just one subset. This is not used for line qualification anymore, due to the variations caused by the various bits of ADSL hardware people use.
The woosh attenuation test looks at the quality of the line across the DSL frequency range and measures how much of the signal reaches your house, the lose should be less than 45db for 2Mbps and 64dB for 1Mbps products. ISPs have the ability via the ECO interface to remotely do this test, but a pass with this test does not guarantee acceptance onto the 1Mbps and 2Mbps limits.
Many ADSL modems will display the equivalent of the woosh test, but these can be inaccurate. Some modems can be as much as 20dB, though the majority are within 2-3dB. For those with very long lines, the Signal to Noise ratio (Noise Margin) becomes critical, ideally a figure above 6dB is needed for most ADSL kit to function.
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