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[j0hn]

It sounds from the OP that the DCOE (Dedicated Centre Of Excellence?), which is who Openreach engineers contact to have any changes made (port swaps, DLM resets etc) , can manually set a specific DLM profile.

When the OP said earlier in the thread...

They offered to enable interleaving on the upstream part of the connection (one of them said he sometimes used to enable interleaving on ADSL connections to reduce packet loss), so I will see what difference this makes.

I was thinking to myself that isn't possible perhaps the engineer is indeed getting mixed up with ADSL, but then he posted a screenshot of interleaving enabled on the upstream.

I've certainly never seen a DLM reset result in both downstream and upstream interleaving. On an ECI cabinet it's always just downstream interleaving that's enabled.

If that's the case they can manually set the profile then it does seem a rather pointless exercise if the DLM continues to run and a few days later simply changes the current profile to remove the manually set change.

There was quite a few DLM related briefings for CP's during 2021 which might also explain it.

https://www.openreach.co.uk/cpportal/updates/briefings?t=category:briefings/super-fast-access

They included a new DLM Stability Policy Trial started in June, extended in October (trialing a new/different stability policy)
There was also a DLM Reset Process Improvement Trial started in December.

It's possible this new stability policy trial starts with upstream interleaving and that's why the OP had it but also possible the DCOE manually set that profile.

I wonder if BlackSheep is around and could enlighten us as to whether the DCOE has the ability to manually set a specific DLM profile (interleaving on/off, G.INP on/off, SNRM target) and if so whether they can make that change permanent and effectively disable the DLM from making further changes.

It's certainly something I've never seen before and wasn't aware was possible but if anyone could do such a thing it would be the DCOE.

[cbdeakin]

@j0hn - That all sounds very interesting.

I guess I'll see if my ISP is able to offer any further help.

[cbdeakin]

I googled 'DCOE openreach' and found this:

https://www.cvf.openreach.co.uk/orpg/home/aboutus/ourorganisation/businessinfo.do

'We also have an offshore team based in Pune, India'.

The engineer said that the tech support team they work with is based in India.

So, quite likely to be the DCOE that the engineer called.

[Alex Atkin UK]

It would certainly be irregular, people can spend months trying to get Openreach to fix much worse problems than what you had and never get referred to that team.

[cbdeakin]

Well, we rely on Openreach to get lines up to a certain standard. Most lines should be able to handle video streaming comfortably (especially syncing over 20-30mbps downstream), if they don't I think it's Openreach's responsibility to fix it if possible, because they own and maintain the lines.

I hope you aren't going to go on about latency again 

[Reformed]

Sorry about the Spanish Inquisition you've been getting on this, cbdeakin. I don't understand it but, then, don't have any desire to do the research that might fill me in so will live in blissful ignorance. Hope it's all getting sorted! 

[cbdeakin]

Cheers.

[Alex Atkin UK]

I'm sure I could have done a better job of explaining the reasoning, coming off a bit aggressive has always been a problem I struggled with.

The thing is, several members of this forum have likely the largest collective knowledge of how Openreach manage things than anywhere else on the Internet and what you were told by the engineer contradicts countless other peoples experiences and what we know about how DLM and line profiles work.

Its not that we were denying you were told what you were, just that there have been so many occasions where engineers make claims that are completely wrong, or explain poorly causing misunderstandings.  Most engineers don't actually know how the DLM works, its not their job to, DLM exists for the very purpose of not needing people to manually tweak things and from past experiences prevents any such tweaking.

If this permanently solves your problem then that's great, but as mentioned earlier, generally any change in procedures has to also be documented to the ISPs.  While yes its up to Openreach to maintain the line to the best of their ability, they generally can't just make random changes that the ISP is not expecting as that can result in a lot of questions from customers that the ISP then cannot answer.  So until proven otherwise its best to assume this was a DLM reset and interleaving could get removed again.

[cbdeakin]

Thanks for your reply Alex. It's all good, no explanation needed. I appreciate your knowledge and experience (and from other members also) regarding how the DLM system works.

You're right of course, it's fairly likely that the DLM will simply undo any changes that Openreach / Openreach engineers attempt to make, as the system is designed to control these things automatically, and adjust them over time based on errors, resyncs etc.

If it can't be enabled as seems likely, I'll just adjust my expectations accordingly!

It's probably fair to say that I tend to be too optimistic when dealing with technology related problems, especially since this is not something I can solve myself.

Sure would be nice, if it 'just worked' though 

[j0hn]

To answer the initial query...

Are there any VDSL modems that can do this?

I believe the Asus DSL models with the Mediatek chipsets like the DSL-AC68U, can possibly do this.

It wasn't something I personally tinkered with but I think Ixel was forcing fastpath when the DLM had interleaved his line a number of years ago.
It's not a simple UI change though and involves sending commands over Telnet and possibly even running a special app from Asus.
It might be worth a search if that is the only way to fix your issue.

It's not a modem I personally recommend to people as I found it to be quite unstable on my line but others like it.

[cbdeakin]

I have a DSL-N16 (mediatek chipset) that I was using before as a modem/router. It was quite good and worked surprisingly well on my line, but doesn't work in modem bridge mode. There's definitely some useful commands that allow the user to do things like restrict which VDSL2 frequency bands / spectrum is used.

Haven't been able to find the thread (with Ixel's posts) that might highlight the telnet commands I would need to use to potentially change interleaving settings, yet.

[cbdeakin]

Had an email back from my ISP, they seem to be saying that it's impossible to permanently enable interleaving (if not set already by the DLM), so I suppose that's that.

They say it's upto Openreach to upgrade their network, which I tend to agree with (even if this isn't realistically going to happen).

It's been interesting to learn that actually, despite what a lot of people were saying on other forums, packet loss in this case is to do with the line itself (nothing to do with other factors, such as the ISP, or home network setup). Aluminium lines are not well understood it seems, I'm sure many people don't know they are even in use.

[cbdeakin]

Hang on, wouldn't changing the DLM stability profile to 'stable' likely cause interleaving to be applied on the downstream / upstream after a short time? There's definitely errored seconds on both the downstream and upstream.

Probably worth asking my ISP to look at this again, since it might work.

These stability profiles are mentioned here:
https://kitz.co.uk/adsl/DLM.htm#dlm_stability_level

Wonder if any ISPs still use the 'Stable' option?

What's interesting about this option, is it is described as "Prioritise stability over speed for IPTV".

Cuckoo is likely using the 'NGA Standard Profile', as they make use of Talktalk's business network.

[g3uiss]

Had an email back from my ISP, they seem to be saying that it's impossible to permanently enable interleaving (if not set already by the DLM), so I suppose that's that.

They say it's upto Openreach to upgrade their network, which I tend to agree with (even if this isn't realistically going to happen).

It's been interesting to learn that actually, despite what a lot of people were saying on other forums, packet loss in this case is to do with the line itself (nothing to do with other factors, such as the ISP, or home network setup). Aluminium lines are not well understood it seems, I'm sure many people don't know they are even in use.

That seems what we would expect here. In ADSL you could have the ISP set SNRM and interleave but not on VDSL which is what other posters have said. At lest that’s been confirmed to you now.

Your next post about stability is an option, but rarely is interleave added upstream so you will likely end up with worse downstream performance and no change to upstream

[cbdeakin]

I think interleaving rarely gets enabled on the upstream, probably because the thresholds on most lines are set high enough for that to be avoided.

It seems that Zen Internet does offer the 'stable' profile option, according to this:
https://support.zen.co.uk/kb/Knowledgebase/Fibre-Optic-Broadband-FTTC-What-is-DLM-and-how-does-it-work

Plusnet seems able to make these changes on request also:
https://community.plus.net/t5/Fibre-Broadband/what-stability-profile-are-we-on-and-can-we-change-it/td-p/1488251