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Author Topic: Target SNR Questions  (Read 4631 times)

goake

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Target SNR Questions
« on: January 10, 2007, 10:18:21 PM »

Hi,

My boadband was upgraded to MaxDSL back in March I think, and I was happy with my stats:

Connection Speed 5664 kbps
Attenuation 32db
SNR 15db

IP Profile of 4500 - which is right.

Happy, until I read your site! As my router is connected straight to the BT master socket I never realied that my internal wiring could be adversley effecting my connetion speed. My internal wiring is bad - telephone sockets in every room, only half of which work because mice have chewed the wiring. So I tried connecting straight from the test socket. Connection speed was 7200 - a vast improvement. Not wanting to redo all the extensions, because I'm lazy, I ordered a NTE5 faceplate.

With the new plate stats were:

Connection Speed 7392kbps
Attenuation 29db
SNR 15db

Waited three days and the IP Profile went upto 6500, which is where it should be.

The router hasn't disconnected once since I changed the faceplate (about a week). I've being monitoring the router stats with RouterStats 2.7g. My SNR drops to 13db at night with the odd blip to 10db but never lower. The software is reporting that interleaving is turned on.

I think that my target SNR has been increased to 15db. I was thinking that if I could get it back to 6db, the extra 9db might get my connection speed upto the maximum?

How do I get this changed? I've read somewhere that if the connecton remains synched for 14 days the taret SNR is automatically lowered. If this is the case how does it actually get applied - I mean to connet at a higher speed with a lower target SNR would require a reconnet, but if its been stable for 14 days this is highly unlikely?

Also, with such a stable connection now, should interleaving be turned off? and if so how do I get this done?

Incidently my router is and old Netgear DG834 v1, with an old firmware. I tried using a higher firmware, but I couldnt make it do what I needed it to do (ie NO NAT and No firewall - I want my firewall on an ISA Server not the router)

Thanks in advance, Glen
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roseway

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Re: Target SNR Questions
« Reply #1 on: January 11, 2007, 08:44:21 AM »

Hi Glen, welcome to the forum.

It looks as though you've done everything right and you're getting a good result. Your target noise margin will (allegedly) come back down automatically if your connection is stable. I don't think that it has to stay up for the full 14 days, but you have to consistently sync at about the same speed without many re-syncs. If that sounds vague, that's because I don't think the details have been published by BT.

The normal way to get interleaving turned off is to ask your ISP to get it done. It might result in a less stable connection, so you need to consider whether it's really important to you (e.g. you're a gamer with fast reactions, and the extra latency is slowing you down).

Eric
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goake

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Re: Target SNR Questions
« Reply #2 on: January 11, 2007, 02:15:17 PM »

Thanks for your prompt reply.

With reference to the latency issue, I'm not an online gamer so I'm not concerned about the extra latency. I was more concerned about the theoretical max connection speed of 7616 kbps.

If i'm currently getting a connection speed of 7392 kbps using a target SNR of 15 db, I was thinking that if my targer SNR was reduced to 6 db then I might be able to hit a connection speed of 8128 kbps - but would need interleaving turned off for that.

Are there any stats that I could look at to determine whether I should leave the interleaving on or not? The excellent monitoring program RouterStats is giving lots of information that I dont really know how to interpret.

Also, is the only way of knowing whether my target SNR has been reduced is to disconnect and reconnect again? My connection has been up over 8 days now, it would be a shame to disconnect just to see if the target SNR has been reduced.

thanks
Glen
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roseway

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Re: Target SNR Questions
« Reply #3 on: January 11, 2007, 03:46:08 PM »

You might be one of the lucky ones who get the full 8128 connection speed even with interleaving applied. There have been several reports of this happening, even though it isn't supposed to. If not, I guess it's your decision as to whether you want to risk instability in return for higher speed. No doubt there are experts who can interpret the error statistics you get from the router or monitoring program and estimate what the result would be without interleaving, but I'm afraid I'm not one of them.

As far as I know, the only way to know that your target noise margin has been reduced is to reconnect. This isn't really a big issue - infrequent reconnections won't affect your connection profile; after all, there are lots of people who use ADSL modems and disconnect every night.

If you're really interested in squeezing the best out of your connection, you might consider getting a router which is supported by the DMT tweaking tool, see http://dmt.mhilfe.de/ (It's in German, but the program has an option to use English). With this tool you can play around with the target noise margin to your heart's content.

Eric
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goake

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Re: Target SNR Questions
« Reply #4 on: January 12, 2007, 08:11:56 PM »

Thanks Eric.

I tried reconneting - same speed, and SNR of 15. I've searched all the forums and so far I haven't found a single instance of where the Target SNR has automatically been reduced. Theres lots of stories where people try to get the Target SNR manually reduced, only a few have been successfull. Lets face it the average ISP support guy probably doesnt understand the conept of 'target SNR' and by the time the request gets to BT, who knows whats been asked for.

Not willing to take on the ISP on this frustrating task I think I'm going to go the DMT route. I've downloaded the tool before, it looked good, but didnt work on my ancient router. Is  there a list somewhere of routers it works with or even a personal recomendation?

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roseway

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Re: Target SNR Questions
« Reply #5 on: January 13, 2007, 08:02:19 AM »

Is  there a list somewhere of routers it works with or even a personal recomendation?

Different versions work with different routers. On the page I pointed you at the supported routers are listed for each version. I use a Speedtouch ST546, but unfortunately with the latest firmware part of the DMT functionality is disabled (although you can still tweak the noise margin). Routers which use Broadcom chipsets (e.g. Belkin F5D7633) are apparently well supported, but I've no personal experience.

Eric
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goake

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Re: Target SNR Questions
« Reply #6 on: January 14, 2007, 12:13:39 AM »

After reading the link I've bouht the Netgear DG834GT which is listed as compatable with DMT. I didnt see an easy way of adjusting the taret SNR, other than using it to send the command 'adslctl configure --snr 10'-whih could have been done by Telnet. I'm I missing something, or is this how to tweak with DMT?

Anyway, very impresed with the results:

Connection Speed 8096kbps
Attenuation 28db
SNR 12db

Which considering I was happy with 5664kbps before I read this web site is a big improvement.

What I dont quite understand though, is why it stops at 8096, there seems to be plentry spare SNR margin to get it upto the maximum 8128, and I'm over the apparent maximum for when interleaving is on?

Any thoughts? Or maybe I should just shut up moaning, and be happy with my 30% increase?
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roseway

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Re: Target SNR Questions
« Reply #7 on: January 14, 2007, 08:19:26 AM »

:)
I wouldn't dream of telling you to shut up moaning.

Almost certainly, what's happened is that your target noise margin has been set by the automatic process to 12dB, and 8096 is the best sync rate which is achieved with that margin. You should be able to tweak it down and get the full 8128.

The noise margin tweaking part of DMT is hidden by default. Under the Special menu select 'Misc options'. Check the box 'Unlock experimental area'. Then click the new 'modemoptions' tab. You can now move the slider up and down by smallish amounts at a time, then click Apply/resync to try out the new value. When you've got it how you want it, click 'Save settings' to preserve the changes. Alternatively you can enter values directly into the modemoptions boxes, but you need to be careful with the values, so that can be a little problematical.

Eric
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goake

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Re: Target SNR Questions
« Reply #8 on: January 14, 2007, 12:05:25 PM »

I've done some experimenting now I've disovered the hidden tab in DMT - thanks Eric.

With no Target SNR modifications, and three different routers, the SNR Margin is always 15db immediately after connecting, so I think I can assume that my Target SNR is set at 15db.

When I adjust the slide bar in DMT, I get an inrease in connection speed, and a corresponding decrease in SNR. However, this only goes so far. Once the speed has increased to 8096kbps any further adjustments made do not make any difference. I now have the slide bar set at 30  (which to me means 30% of the original 15db, so 5db - is that right?) and everytime I connect I get a connection speed of 8096kbps, but the SNR is different everytime, ranging between 13.2db to 11.4db. This sugests to me that the Target SNR is being exceeded, but the limiting factor is the maximum speed, which in my case is 8096kbps - which must have something to do with interleaving?

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roseway

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Re: Target SNR Questions
« Reply #9 on: January 14, 2007, 01:23:39 PM »

Ah yes, I'd forgotten about your being interleaved. That's probably the explanation, and of course even 8096 is faster than you're supposed to be able to get with interleaving.

I'm not sure that the slider position translates so precisely in the way you suggest. I prefer to enter values in the modemoptions section, and there you can increase as well as decrease the target noise margin relative to how it's set by BT. I would have expected the slider to work in the same way.

Eric
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goake

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Re: Target SNR Questions
« Reply #10 on: January 14, 2007, 02:10:38 PM »

I did just try moving the slider in small increments. Unfortuneately I tried it the other way - got distrated by the kids and synched at a much lower speed for about an hour. Now my IP Profile is at 5000. Suppose I'll have to wait 3 days before it goes back, bit unfair of BT that - 1 hour for the profile to go down, 3 days to go up.

Think I'm going to wait the 3 days, then ask for interleaving to be removed and go from there. Thanks for all your help and guidance.
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roseway

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Re: Target SNR Questions
« Reply #11 on: January 14, 2007, 06:50:13 PM »

These systems are designed to test your patience. :)

Eric
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