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Downstream Attenuation ADSL2 vs ADSL2+

Community Veteran
Posts: 3,188
Thanks: 20
Fixes: 2
Registered: ‎31-07-2007

Downstream Attenuation ADSL2 vs ADSL2+

Oddity I just noticed tonight, if connecting my router under ADSL2 my Attenuation is 47 but if under ADSL2+ it is 52.
kitz reports the best it can be:
52db gives a connection speed of 4512 kbps, with IP Profile of 3500 kbps
47db gives a connection speed of 6400 kbps, with IP Profile of 5500 kbps
Currently it is connecting at 3065 kbps with 2700 IP Profile
So question is why is there a difference?  It makes a 30% speed difference, ok I'm happy with the speed I get just puzzled as to why its different.
Unvalued customer since 2001 funding cheap internet for others / DSL/Fibre house move 24 month regrade from 8th May 2017
2 REPLIES
Community Veteran
Posts: 38,460
Thanks: 1,031
Fixes: 62
Registered: ‎15-06-2007

Re: Downstream Attenuation ADSL2 vs ADSL2+

Because on ADSL2+ it tries to use a lot more of the higher frequencies and, where the router takes that into account, that will dramatically increase the reported average attenuation
x47c
Grafter
Posts: 878
Thanks: 1
Registered: ‎14-08-2009

Re: Downstream Attenuation ADSL2 vs ADSL2+

The attenuation reported by the router is only an "averaged out" summation of the various attenuations at each of the frequencies used by the ADSL signal.
The mathematical calculation method by which the router arrives at the reported overall attenuation figure will have been laid down in the standards to ensure all routers do it the same way.  In any event the answer is rounded to the nearest whole figure so on the same line the real value might be 33.5 which some might report as 33 and others round up to 34.
Its a well known rule of thumb that switching to ADSL2+ will increase the router's reported attenuation figure by around 3 or 4 dB
'tis the same for SNR margin figures.  In practice the minute by minute variation in SNR margin being seen by us during the day all is probably down to reasonably large variations in the margin on just a few individual frequencies rather than the SNR margin over the whole frequency spectrum varying up and down in unison.