Too bad when that was case I didn't know how to check SNR on particular tones and bit loading. Perhaps I would have answer. However, I've noticed once also strange change on upload despire of the same bit-loading and the same power output. I've found other people have similar issues:
http://forum.kitz.co.uk/index.php?topic=13083.0

Best regards
konrado5

I guess you are not in UK. If your country's ISPs are anything like ours then the sync-time Target NM is almost invariably a multiple of 3dB, e.g. 6dB it looks like in your case. The sync speed for that connection session is determined by that sync-time Target NM. What you seem to be forgetting is that by the time the modem has disconnected and reconnected, and you have had time to login to its GUI and view its stats the NM has moved on due to noise variation. In other words, all the NMs you are quoting are not the sync-time Target NMs that gave rise to the sync-speeds you are seeing and so you can't relate them in the way you are attempting to.

You just can't be that precise!

All you say about bins, tones and powers is beyond me and I believe what you are asking calls for a deep theoretical thesis on DSL technology and I don't believe that this is the forum to supply that.

In reply to a post by XRaySpeX:

I guess you are not in UK. If your country's ISPs are anything like ours then the sync-time Target NM is almost invariably a multiple of 3dB, e.g. 6dB it looks like in your case.

It's a case. Target SNR margin in my ISP is 6 dB.

The sync speed for that connection session is determined by that sync-time Target NM.

I know it.

What you seem to be forgetting is that by the time the modem has disconnected and reconnected, and you have had time to login to its GUI and view its stats the NM has moved on due to noise variation.

I did reconections during flat SNR period for example 10 minutes period. Moreover, as I've had 1241 kbps upstream, my SNR margin was continously no more than 6.6 dB during very long time. Suddenly, as I've rebooted router I've got higher synchronization rate and SNR margin despire lower power output measurement. Similar case was for download, as my ISP changed cap from about 18800 kpbs to 25000 kbps. During stable SNR margin period I've had either 17200 kbps with SNR margin 6.3 dB or 17800 kbps with 6.1 dB SNR margin. Now i know how to check SNR on tones, however on new DSLAM I don't see this case. I have always 6.1 dB immediately after synchronization rate and during 10 minutes period differences now higher than 100 kbps.

All you say about bins, tones and powers is beyond me and I believe what you are asking calls for a deep theoretical thesis on DSL technology and I don't believe that this is the forum to supply that.

Could you recommend any other forum where people know about details?

Best regards
konrado5

Edited by konrado5 (Tue 04-Feb-14 17:16:09)

For all anyone knows the figures displayed may have rounding errors and mistakes in the display maths - plenty of instances where firmware says an impossible set of figures but people have a good connection.

But without snr values and attenuation for each bin it is hard to say. Here is another puzzle...

Some routers supply the SNR/attenuation values based on a single tone in either direction.
Some routers average it out across the bins to arrive at a consensus value.

Most of the time the two are very similar, and are irrelevant to how each bin loading is calculated.

Next step beyond here is the people who work on the micro-code and standards e.g.

http://www.broadband-forum.org/

Among router manufacturers I am willing to bet many are just using reference code and do not actually understand the full mathematics and oddities that RF can throw at the DSL chipset.

In reply to a post by MrSaffron:

For all anyone knows the figures displayed may have rounding errors and mistakes in the display maths - plenty of instances where firmware says an impossible set of figures but people have a good connection.

I think it wasn't calculation error. As I've had strangely lowered synchronization rate and SNR margin I've had also more errored seconds. I suspect I've had then many tones disabled but why these tones would be disabled? It would require siginificant SNR drop on many tones and in turn it would be noticeable on SNR margin.

Some routers supply the SNR/attenuation values based on a single tone in either direction.
Some routers average it out across the bins to arrive at a consensus value.

I've found something about bit amount calculation for every tone (page 204).
http://books.google.pl/books?id=m77kZl71gysC&printse...

It seems attainable synchronization rate is not depended on the way router measure SNR margin, it is depended only on SNR on particular tones.

How is power output value calculated? Is it average across all used tones power?

Moreover, I've written other post:
http://forums.thinkbroadband.com/technical/f/4302367...

Best regards
konrado5

Edited by konrado5 (Tue 04-Feb-14 19:40:34)

Yes, that seems the right sort of forum for these sort of deep considerations.