VDSL Performance & Tuning

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202 posts

Master Geek

#659316 20-Jul-2012 20:44

For those who do not want to enable Telnet to adjust the SNRM can use this alternative method.

Save a copy of your Fritzbox settings.

Here is how to do this. You will need to assign a password to the file for saving and restoring it.

A export file will be saved to your PC.

You can open this file with Notepad.

Once opened, CTRL + F to bring up the search function and search for ( DownstreamMarginOffset )

You should then see the line ( DownstreamMarginOffset = 0 ; )

-10 to -100 is to reduce your SNRM for increased speed and 0 to 100 is to increase the SNRM for Stability.

Save your changes.

Here is the screen to restore the Config file.

maxzzz

86 posts

Master Geek

#659515 21-Jul-2012 12:53

Are you talking about backing up the Fritzbox config file and then changing the SNR and then restoring it back to the Fritzbox?

Yes Napster, I was talking about something along those lines, but without using the Web interface directly.
To add to your explanation about getting the configuration backup and changing some parameters before restoring, we need to do something else otherwise the fritzbox will not accept the manually tweaked configuration.

In fact we need to disable the checksum to force the fritz to accept the new configuration, this is simply done by adding the line:
NoCheck = yes;
just before **** CFGFILE:ar7.cfg. If you want to use this technique, I also recommend using Notepad++.

But I have done it slightly differently, with the use of a free software written in Java by a Fritz enthusiast Oliver Metz, which is called Fritz!Box Export Editor. Its original forum page is here. But you can also find a direct download link of version 0.5.3 from this website.
It is in German, but with the help of Google translate I was able to use it very easily, here is how:

First, I strongly advise you to do a backup of your original configuration (as explained by Napster in the previous post) just in case. Moreover this technique is not recommended if your line attenuation is high because it will only make your line more prone to random disconnections.

Open the FBEditor jar file (you need to have Java installed)

It will ask for the url to connect to the fritz, you can leave this by default

Then it will ask for the password to access the router, if any

Once the editor is open, you can retrieve the fritz current configuration by doing CTRL+E or using the menu

You can then use CTRL+F to find a specific part and change the values directly in the editor,
here I have decreased the target SNR by 6dB, I do not recommend going below this point.

Once you have made your changes you can send them back to your fritz and have it reboot with the new parameters in one go by using the menu as shown below:

After reboot you can go to the web interface and you should see this in the case of lowering the SNR, the radio button in "Intended signal-to-noise ratio" should not appear because it's value is not within the range available from the web interface anymore.

Important note: I provide all this information for educational purposes only, you take your own responsibility if you want to make any change to the configuration that is not directly accessible from the web interface.

SamF

1578 posts

Uber Geek

Trusted

#659520 21-Jul-2012 13:14

maxzzz:After reboot you can go to the web interface and you should see this in the case of lowering the SNR, the radio button in "Intended signal-to-noise ratio" should not appear because it's value is not within the range available from the web interface anymore.

So does anyone know what the "Intended signal-to-noise ratio" options in the Fritz!Box actually change the values to? I'm guessing it's just adding to the SNR value but since 12 is the maximum profile available on the DSLAMs this makes no difference if you are already on an SNR of 12?

Also maxzzz, in an earlier post you seemed to indicate that you had a method of influencing the DLM profile that you were on, is that the case (other than manipulating SNR of course)?

I guess with the SNR mod however, we could reduce the SNR by 3 to get onto a 9 SNR DLM profile?

On a slightly different subject; Does anyone know what adjusts the 'Bitswap' option on the Fritzboxes? This doesn't seem to be a DLM option. Is the Fritz determining if this is on or not?

maxzzz

86 posts

Master Geek

#659525 21-Jul-2012 13:26

The values from the "Intended signal-to-noise ratio" web interface are from left to right: 40/30/20/10/0.

On a previous post I was only saying that tweaking my snr did not make the DLM faulty, DLM continued to work as it should by finding the corresponding profile that was the best with my new 'tweaked' config. But I did not influence DLM in any way directly.

As for the DLM profiles, they do not allow to go below 12dB, like on ADSL, this is a choice that Chorus made. So you can use the techniques explained earlier to reduce your SNR by any number (you can have a SNR of 6,7,8,9 even 8.5 etc) but this has not equivalent on the DLM profiles. DLM seems to only work with VDSL profile, interleaving, bitswap and Impulse Noise Protection.

SamF

1578 posts

Uber Geek

Trusted

#659551 21-Jul-2012 14:49

maxzzz: As for the DLM profiles, they do not allow to go below 12dB, like on ADSL, this is a choice that Chorus made. So you can use the techniques explained earlier to reduce your SNR by any number (you can have a SNR of 6,7,8,9 even 8.5 etc) but this has not equivalent on the DLM profiles. DLM seems to only work with VDSL profile, interleaving, bitswap and Impulse Noise Protection.

From the official Chorus documentation I've seen, there are 2 different standard SNR levels available with VDSL DLM profiles: 9db and 12db. Did DLM continue to work when you were using 'non-standard' SNR settings (eg 6db)?

Napster: How does maxzzz's experience compare with your own in terms of DLM functioning or not functioning correctly?

Another question which you guys may know the answer to: The spectrum graphs seem to indicate SNRs of up to 65db, how does this correspond to the 9-12db that we're talking about here?

SamF

1578 posts

Uber Geek

Trusted

#659554 21-Jul-2012 14:58

I noticed my spectrum graph occasionally displaying odd results like below:

Sometimes it's even bigger jagged with more gaps than this but it's very hard to capture as it's only brief.

Does anyone know what this is?

maxzzz

86 posts

Master Geek

#659563 21-Jul-2012 15:00

I have the same thing, it seems to be a small bug in the web interface during updates.

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SamF

1578 posts

Uber Geek

Trusted

#659564 21-Jul-2012 15:01

hmm, ok, I thought it could be some kind of indicator of line issues.

maxzzz

86 posts

Master Geek

#659565 21-Jul-2012 15:04

SamF:
From the official Chorus documentation I've seen, there are 2 different standard SNR levels available with VDSL DLM profiles: 9db and 12db. Did DLM continue to work when you were using 'non-standard' SNR settings (eg 6db)?

Do you have any links to this documentation, I was not able to find anything relating to SNR. I thought that only other players (Vodafone, Orcon, etc) were sometime using 9dB snr on their own equipment for ADSL2+.

And to answer you question, yes DLM continued to work.

Napster

202 posts

Master Geek

#659590 21-Jul-2012 16:32

It seems for now that 8b runs on the 12dB training margin and 17a runs the 9dB profile.

@Max

Ah yes my apologies, your method is the correct way to change the SNRM.

maxzzz

86 posts

Master Geek

#659591 21-Jul-2012 16:36

Napster: It seems for now that 8b runs on the 12dB training margin and 17a runs the 9dB profile.

Hum, that makes sense.

Does someone know why Chorus chose to shape the maximum upload speed to 10Mbps on VDSL2?

SamF

1578 posts

Uber Geek

Trusted

#659592 21-Jul-2012 16:37

So Napster, what was your experience with adjusting SNR and DLM, did you say that DLM stopped working for you when you started playing with SNR figures?

Napster

202 posts

Master Geek

#659593 21-Jul-2012 16:47

When i had adjusted my SNR to around 16dB i think it was, i had line uptime of over 20 days with no DLM profile change triggered.

Soon as i reset back to default my line profile changed after 7 days. I took me around 3 months to get onto the 1ms profile lol.

If i had left it alone it would have maybe been 2 - 3 weeks for DLM to switch to DLM 1

SamF

1578 posts

Uber Geek

Trusted

#659596 21-Jul-2012 16:50

Doh, 3 months! That's the only problem with mucking around with this stuff, DLM changes only happen weekly after the first 10 days so it takes freakin' ages to do any kind of experimentation!

So I take it you weren't successful in getting any kind of better latency by adjusting the SNR?

Napster

202 posts

Master Geek

#659604 21-Jul-2012 17:04

Not very successful at all unfortunately.

If you see in the VDSL documentation, 4 days of uptime and good error count should trigger a profile change.

What i did notice though, lets say that if the line became unstable and DLM moved you from DLM 1 to DLM 2 then to DLM 4 that it would take around 6 days of uptime to drop from DLM 4 to DLM 2 and then around 3-4 days to switch to DLM 1.

Because i was on DLM 8 i had noticed this affect. I actually had a profile change after 3 days.

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