[Info] [Erfahrungsbericht] Powerline an VDSL 35b: FRITZ!Powerline 1220 vs. devolo Magic 2 – massive Unterschiede bei DSL-Störungen und eine Lösung

[wg2003]

Hi

If the VDSL Performer status is 'yes', then I presume your Devolo are communicating with the Fritzbox via TR-064. However, at some point in FritzOS, I remember I had to activate TR-064 (it was as a separate tab), but because I'm on FTTP, I can't see it, or they have deactivated it.

You used to be able to download the support information using the Devolo app for Windows, but I don't know if it's still the case. I remember they tried to retire the Windows app in favour of Android and iOS apps because these days, most use their phones to set up everything.

I'm on the same version of tgc Devolo app for Android, and I use MS Outlook app as my email client. Try setting up a Microsoft email address and use the app to see if you're more successful in getting the Zip file.

 

[wg2003]

TR-064 in FritzOS is configurable in Permit Access for Apps in Home Network > Network > Advanced Network Settings

Produktentwicklungen rund um FRITZ!

Hier gibt es Informationen rund um die FRITZ!Box zu Schnittstellen und Protokollen. Wir freuen uns über Ihr Interesse! ✔

fritz.com

 

[Ganzir]

Thanks for pointing me in the right direction!

I managed to generate a ZIP file using devolo Cockpit 5.2.0.185 under Windows. The DSLCOEXISTENCE entries were indeed present in the .cld files, but Base64-encoded, which explains why my initial text search found nothing.

After decoding the files, I found the following entries on both my Magic 2 adapters (MT2999 and MT3157):

DSLCOEXISTENCE.GENERAL.ENABLE=YES
DSLCOEXISTENCE.GENERAL.RUNNING=YES
DSLCOEXISTENCE.GENERAL.GATEWAY_SUPPORTS_TR064=YES
DSLCOEXISTENCE.GENERAL.GATEWAY_COMPATIBLE=YES
DSLCOEXISTENCE.GENERAL.STATUS_CODE=-231
The diagnostics also report:

• DSL profile: 35b
• DSL link status: Up
• Gateway: Fritzbox
• DSL information queries: 53 / 43
• Measurements: 11 / 13
• DSL disconnections: 0 / 0
• Target power mask applied: YES / YES

Interestingly, both adapters report mimo_vdsl17a as their configured power mask profile, although the DSL connection uses profile 35b. The available profiles also include mimo_vdsl35b.

This is strong evidence that the adapters are actually obtaining DSL connection information from my FRITZ!Box 7690, rather than merely identifying it as compatible.

Two questions remain:

1. Do you happen to know what status/error code -231 means?
2. Is the use of mimo_vdsl17a on a VDSL 35b connection expected behavior?

In any case, thanks again for your help. Without your suggestion to inspect the diagnostic dumps, I would probably never have found this information!

 

[wg2003]

Did you change the profile on the Devolo adapters? There's an option to have either Profile 17 or 35. This is done in the Powerline settings of Devolo (I have an English version.) Please note that you would need to do it on *each* Devolo adapter, not just one of them.

Yes, the adapters query the Fritzbox for the SNR margin and, from what I remember, also errors. This influences the operational mode of Devolo adapters.

With Devolo Performer, I found the impact of powerline on my DSL line at the time minimal, if not at all.

 

[Ganzir]

Thanks for the clarification!

I checked the Powerline settings on my devolo adapters. They are currently configured as follows:

- Automatic compatibility mode: Enabled
- Transmission mode: MIMO
- VDSL profile: 17a (default)

My actual DSL connection uses profile 35b.

According to the description in the devolo web interface, automatic compatibility mode attempts to detect interference and dynamically adjust the transmission power to achieve the best possible performance without disturbing the DSL connection.

This raises an interesting question: Does the manually selected VDSL profile (17a/35b) have any effect while automatic compatibility mode is enabled, or is it only used as a fallback when automatic interference mitigation is disabled or fails?

The diagnostic dumps report "DSLCOEXISTENCE.GENERAL.RUNNING=YES" and "GATEWAY_COMPATIBLE=YES", while the configured power mask remains "mimo_vdsl17a".

So far, my VDSL connection has remained stable, with no CRC errors or errored seconds observed during testing. Cockpit currently reports approximately 341 Mbit/s between the two Magic 2 adapters.

For now, I intend to leave automatic compatibility mode enabled, since it appears to be working well. However, I'm curious whether changing the selected profile to 35b would make any difference while automatic mode is active.

 

[wg2003]

I'd presume that all is done automatically and the specific settings are ignored. However, your log files appear to contradict that, unless the adapters are really working within a specific frequency range only (i.e. never go above 35 MHz, but continue operating within the 2-17 MHz range). Devolo calls this a mitigating profile. It's just my speculation because I know very little about the electrical aspect of Devolo working, and I could even be wrong with this speculation.

It'd be interesting if you switched off the automatic profile and selected 'full power' in Devolo adapters (on all of them) to see if this has an impact on errors. I couldn't test that at the time because my DSL line was subject to interference caused by someone else's electrical equipment. My powerline still suffer from the interference even with my FTTP: it shows when the speed between adapters goes down; normally it's between 600-800mbps but when this electrical interference occurs, it goes down to 100mbps, or even 0 Mbps sometimes. I suspect it's a boiler or something similar because it occurs on cold days in the winter.

Normally powerline adapters get a very bad reputation for what they are, and my testing of Netgear ones had confirmed that. However, it shows that superior products like Devolo adapters can successfully be used with DSL lines without causing too many issues. Not so much if you have general interference, but even then, my Fritzbox comes to a halt, so it's not a powerline/non-powerline issue, but a more general issue of impact of interference. At the time, when Openreach engineers (in the UK, Openreach manages the whole telecoms network for all internet service providers) were here to address the issues of my problematic telephone line, they couldn't understand that. However, I now think that they knew where the problem was and just used Devolo as a scapegoat.

I just wish Devolo updated their firmware and introduced more features with it, such as an ability to switch on/off LAN ports, determine the speed of each port to conserve energy (100 Vs 1000mbps) or allow configurable QoS amongst other features.

 

[Ganzir]

Update: devolo Magic 2 – Automatic Compatibility Mode vs. Full Power

Following wg2003's suggestion, I ran another experiment today to see how disabling the automatic compatibility mode affects my VDSL connection.

My setup:

• FRITZ!Box 7690, VDSL2 profile 35b, full vectoring
• DSL sync: 144,307 / 42,324 kbit/s
• Approximate line length: 410 m
• SNR margin: 6 / 7 dB
• devolo Magic 2 LAN (MT:2999) and Magic 2 LAN triple (MT:3157)
• Firmware: 7.12.9.142

I disabled automatic compatibility mode on both devolo adapters and selected full transmission power.

According to devolo Cockpit, the G.hn link rate increased from approximately 341 Mbps to 447 Mbps.

However, the DSL error counters subsequently increased dramatically.

With automatic compatibility mode disabled:

• Corrected DTUs (last 15 minutes): 439,130
• Uncorrected DTUs (last 15 minutes): 45
• CRC errors (last 15 minutes): 20
• Errored seconds (ES): 120 / 1
• Severely errored seconds (SES): 3 / 0

Interestingly, DSL synchronization remained unchanged at 144,307 / 42,324 kbit/s, and the SNR margin stayed at 6 / 7 dB.

I then re-enabled automatic compatibility mode on all devolo adapters.

After re-enabling automatic compatibility mode:

• Corrected DTUs (last 15 minutes): 7,229
• Uncorrected DTUs (last 15 minutes): 0
• CRC errors (last 15 minutes): 0
• Errored seconds (ES): still 120 / 1
• Severely errored seconds (SES): still 3 / 0

That's a reduction of approximately 98.4% in corrected DTUs, with no additional errored or severely errored seconds recorded.

The minimum effective downstream data rate, which had dropped as low as 131,075 kbit/s during the experiment, subsequently recovered to 142,249 kbit/s.

Conclusion

The results strongly suggest that devolo's automatic compatibility mode is doing a very effective job of reducing interference with my VDSL connection.

What I find particularly interesting is that the substantial increase in DSL errors was not reflected in either the synchronization rate or the reported SNR margin.

Of course, this experiment does not establish whether the improvement is specifically attributable to the TR-064-based VDSL Performer functionality or to other mechanisms within the automatic compatibility mode.

For my particular setup, connection stability is far more important than maximum Powerline throughput. We expect to have three people working from home simultaneously, so DSL interruptions are something I particularly want to avoid.

I'll therefore leave automatic compatibility mode enabled permanently. The additional G.hn link rate simply isn't worth the increased DSL error rate.

Thanks to wg2003 for suggesting the experiment. It turned out to be quite revealing!

 

[wg2003]

Interesting, though unsurprising, results.

Changes to SNR margin and consequently speed link can be automatically adjusted by your DSLAM (thanks to DSL Automatic Management System). They don't happen immediately, but over a period of time. A noisy line can have a lot of errors which will result in changes in SNR: the higher the SNR, the less noise on the line. This also depends on whether you're on so called fast path or interleave, and its depth. Fast path offers a higher sync speed and more noise, whereas interleave is for lines that suffer from problems.

However, changes to SNR margin don't have to happen at all, and all depends on how the line is provisioned. For example, for my noisy line, the SNR never went down to 3db as it'd mean more disconnections and less stability overall.

Here's more information on how DSLAM works, though this is for the UK: https://kitz.co.uk/adsl/DLM_system.htm

 

[Ganzir]

Thanks for the explanation and the link!

That makes sense. I wouldn't expect the DSLAM to react immediately to a relatively short period of increased interference, especially since the connection remained synchronized throughout the experiment.

My FRITZ!Box reports G.INP enabled in both directions, with INP values of 54.0 downstream and 28.5 upstream. That probably helped the line cope with the substantial increase in transmission errors.

What I found particularly interesting was how quickly the error counters responded to the changes in the devolo settings, while both the synchronization rate and SNR margin remained completely unchanged.

With automatic compatibility mode disabled, corrected DTUs reached 439,130 within 15 minutes, accompanied by CRC errors and severely errored seconds. After re-enabling it, corrected DTUs dropped by more than 98%, with no further CRC errors or errored seconds recorded.

So even though the DSLAM hadn't adjusted anything, the difference in line quality was immediately measurable.

For me, the important thing is to avoid sustained interference in the first place rather than relying on DLM or error correction to compensate for it. With three people potentially working from home simultaneously, reliability is considerably more important than squeezing another 100 Mbps out of the Powerline connection.

In any case, this experiment has given me considerably more confidence in devolo's automatic compatibility mode. I'll be leaving it enabled.

Thanks again for suggesting the test!