The other day I noticed that my 2820 was connected in G.992.3 mode instead of the normal G.992.5, and I also noticed that the downstream attenuation was being reported as 39dB, instead of the 43dB which it was on G.992.5. The actual sync speeds were relatively unchanged at approx 5300kbps down and 1126kbps up. I thought it was a "glitch", and restarting the router restored the G.992.5 mode, and 43dB attenuation.

This morning I decided to have a little play, to see what upload speed I would get if I used G.992.5 Annex M, so I enabled it on the control panel at my ISP (I'm using an Andrews & Arnold LLU connection supplied by BE), but I forgot to change the mode on the router, and again I got G.992.3 with an attenuation of 39dB. When I changed the 2820 to Annex M mode, my line attenuation was then 48dB (4885kbps down, 1850kbps up) !

I'm confused - my router is using fewer downstream bins, but the attenuation is now higher ? :?

Can someone please explain this anomoly ?

Draytek routers report the LOOP attenuation, not the downstream.
So that attenuation is the downstream PLUS the upstream.

Sorry, but I find that hard to believe. I've had routers that report US and DS attenuation separately, and they all report very similar DS numbers.

runningdeere wrote: Draytek routers report the LOOP attenuation, not the downstream.
So that attenuation is the downstream PLUS the upstream.

The Loop attenuation on my 2820 is identical to the figures given on a Netgear, Speedtouch or Zyxel routers..... 24db adding the 2 figures would raise the attenuation to 37db which it certainly is not.

Yes, and someone on another forum has also reminded me that if you telnet into the router and issue "show status" and then "show adsl" commands, the upstream and downstream attenuation are shown separately, and the downstream attenuation matches the Loop Attenuation reported on the router status page.

Anyway, I think I've got my head around this..... the reported attenuation is the average attenuation of all the bins used, and this is the reason why the downstream attenuation always rises when ADSL2 or 2+ is used, because you are using higher frequencies which have higher attenuations. With Annex M, you are using some of the lower-frequency bins for upstream which would have been used for downstream, and these lower frequency bins have a lower attenuation. The remainder of the bins used for downstream will have higher attenuations, so the reported attenuation is higher.

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