Billion UK Forum

Hi,

Quick question: "How do you know when you've gone to far with tweaking?" I'm using the 7800N at the moment, SNR at 4.1 after a little tweak (previously around 6db) which is giving me just under 14mb down. I'm wondering what to expect if i take it down further? I know it makes the line unstable etc but should i expect the internet to be dropping, webpages not loading, slow internet? Will I be able to track it in the system log, or will i notice my connection time (currently 1 Day(s) 18:15:28) will reset every time the internet drops?

I want to be able to increase sync speed to 15Mb but obviously would like to know when i've gone too far.

Cheers

Jayson

You'll know when your connection frequently drops.

If you reduce the SNRM too much, then it won't have any wriggle room when it drops naturally in the evening or at peak times and the first sign will probably be lag.

I used to tweak mine on a 50dB Downstream Attenuation, but found that reducing it to 4.5 from 6 was the best it would take as at the time, it was dropping to 0.4 around 11.00pm - sometimes it would hang on and sometimes it wouldn't, but when it did the lag was quite bad.

You could try reducing it to 3dB and see how it goes, but I doubt that you will be able to achieve that sort of increase as you would need to drop it about another 3dB from your 4.1 and depending on other factors http://www.kitz.co.uk/adsl/linestats.htm

Thanks for getting back to me Tom.

I will keep an eye on the SNR - I'm fairly certain it drops/ increases no more than 1db throughout the day and considering it's rather warm in the day at the moment and cold at night i would think nows a good time to record any fluctuation. Your drop to 0.4 sounds massive, never had anything like that!. My attenuation is 34.0 and judging by the calculator on the link you gave me my line is around 2.5km from the exchange although line of sight is 1km.

Cheers for the link by the way, I've read a lot of these explanation pages but that one really sums everything up nicely.

Lastly when my connection drops will this be recorded in the system log in my router settings?

Cheers

Jayson

I don't think I ever checked the System Log when it dropped during those conditions, so I'm not sure what it would record if just the 'net dropped and the DSL stayed up.

I know the Uptime Status would be different to the Connection time in those circumstances.

As a general guide, dividing your Downstream Attenuation by 13.81 (think that's covered in Kitz) will give the approx. length of cable between you and the exchange, although the Attenuation can vary to that because of the quality of the wire and joints/weather and a bad joint can increase the actual/recorded Attenuation - mine often varies by 0.5dB.

I think that at the time my SNRM was dropping like that was when there was a problem at the cabinet, but these days (when I check), I don't think it has dropped below 2.7dB.

While lower SNRM can increase your sync speeds, it can also make the connection less solid - as you said.

While the router will hold onto the connection down to silly-low margins, the throughput graph shows regular dips, which I assume are issues with the connection - so basically lose you more throughput than you gain with the faster sync.

For me, I just fire up Task Manager and leave it on the Networking tab. Go to View / Network Adapter History, and turn on Bytes Sent & Bytes Received (I turn off Bytes Total).

Then, go to http://www.thinkbroadband.com/download.html, and download the 200MB file. Task Manager should show a solid yellow line for the download - no dips & no dropouts.

If I have a bad connection I'll probably see a couple of dropouts during that download, so I up the margin. Those dropouts are just stealing some of the extra bandwidth you bought with the lower margin. Repeat until things run reliably.

Complication is that you will occasionally see dropouts even on a good connection, so can take some time to be sure your SNRM figure is reasonable.

Personally, I ended up on 60 / 4.0dB as a reasonable compromise.

Of course, if you're on a BT-based line, BT's DownLoad Monitor may cut in and limit your download speeds (I have this at the moment, waiting until it catches up with my new sync speed). Nevertheless, you can still monitor consistent download speeds, even if they are throttled by the DLM.



One other thing I do is to use RouterStat's alarm function:-
1) setpoints:- config alarm if Rx noise margin is below 3dB for more than 60 second.
Obviously, this needs to be lower than the speed you get for your configured SNR, else you'll just trigger endless alarms!
You could try a lower figure (2dB?), if that works for you.

2) config: set the alarm reboot URL as http://192.168.n.n/snr.cgi?snr=60 (n.n being your router's address). (I'd suggest you also log all alarms on this page, so you can monitor.)
This is not the default "really reboot the whole router" function, which will make all computers lose their connections.
This just re-triggers the SNR change (even if there's no change), which will disconnect & reconnect the internet connection WITHOUT KILLING ANY CONNECTIONS THROUGH THE ROUTER. Even video streaming seems to pick up once the internet has re-synced.

3) actions: turn on "reboot router" (and perhaps "audible alarm").
Triggers the re-sync if SNR drops into the unreliable zone.

4) Click settings / Apply & Save.

This will re-sync any time the SNR drops low enough to be unreliable. Be careful not to set the detection point too close to your configured SNR, else you'll trigger lots of re-syncs, which may make DLM think your line has a problem.

You can also set a reboot if Rx margin goes above a high point (eg 6, 7, 8 dB). But, again - beware lots of re-syncs, which may make DLM think your line has a problem. I suspect this is pretty pointless if you're on a BT-based line, as their DLM will take a while to notice your new, faster sync, and you may well have re-trained to a lower sync again by the time it eventually notices.



One other thing to note - this makes for a very easy way to fiddle with the router's SNR - just configure a different margin in the "reboot" URL, then click "reboot now". Just don't forget to use Settings / Apply & Save again, if you want to keep that setting.

cheers, Martin

PS the RouterStats thing is particularly useful now that my Billion is causing Firefox to crash.