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[Newmski10]

Hi guys, my first post on here, so here goes.

I've just recently joined up with Sky broadband, and im connected to the LLU ect. Im pretty happy with my downstream speed of 5192 in my router stats. I've currently got Sky looking at upping that too. But im just wondering, with my upstream connection. It says Line attenuation is 31.7 dbs and my downstream attenuation is 52.5. I thought that attenuation was quality and length of the line? So how come my Line attenuation of upstream and downstream is not the same? Secondly i am syncing at 509 kbps on my upstream. My noise margin is 16 dbs at the moment, but will go higher during the day. Does the noise margin on the upstream work the same as the downstream? So basically if it will go as low at 6dbs (like my downstream) i have around 10 dbs to play with? Therefore being able to sync higher. I don't know if this will make any sense to anyone  but any help will be much appreciated 8) Cheers 

[waltergmw]

Hi NewMiskl & welcome,

You need to hang around here for a few months to glean some greater understanding.

Attenuation values vary with frequency and all modems do some sort of averaging algorithm on the downstream value.
Look at the picture here of a 2Wire diagnostics print out to see real attenuation values averaged and at 300 kHz.
http://forum.kitz.co.uk/index.php/topic,8633.msg182260.html#msg182260
It would be worth waiting for others here to give you an explanation of how the upstream works.

If you look here:-

http://www.kitz.co.uk/adsl/max_speed_calc.php

you'll see your line is performing better than Kitz's estimates so I'd just sit back and enjoy the music !!!!
Otherwise you'll spend a lot of time probably with very little real gain.

Kind regards,
Walter

[roseway]

It would be worth waiting for others here to give you an explanation of how the upstream works.

As far as I know, upstream uses the same type of algorithm: the attenuation is averaged in some way over the range of frequencies used for the upstream part. As the upstream part uses lower frequencies than downstream, the reported attenuation is lower. In addition, the upstream part may be capped (*) so that the speed doesn't reach what is theoretically possible, so you end up with a higher upstream noise margin than the target (usually 6 dB).

* For example, BT ADSL Max is capped at 448 kbps upstream speed, so most users on this system have quite high upstream noise margins.