In reply to a post by WWWombat:

All 3 spikes look like resyncs, although the third is obviously of lower duration.

As another posted stated, a new PPP session (as requested by the router, or by a direct PC connection) will have no effect on the need for (or amount of) interleaving or FEC.

As Bald_Eagle stated, DLM tends to look at the average error counts over the last 24 hours, and the number of resyncs, and decides whether it needs to limit your connection speed, or add interleaving.

However, it most certainly isn't as fast at taking things away again when any problems disappear. You can expect to wait for between 1 and 4 weeks for that to happen - so patience is required.

And even then, there's no guarantee. My first line got interleaved after 48 hours, and it stuck forever.

Thanks - I did reset the router for a new PPP session (second spike) and it had no effect on interleaving or my IP profile and actual througput. Contemplating buying a HG modem and unlocking to check line stats but figure it is best just to leave the ECI on and wait for interleaving to be removed in time - if it ever does!

Pings have doubled but I've not seen any change in throughput since having this line, kind of annoying as latency is more important than out and out speed to me. It is a pity that DLM can act so quickly on potential problems but seems to take so long to resolve them.

Does anyone know if a regrade to a 40/10 service from the 80/20 forces a DLM reset, could be an option in some cases if you had a monthly sub.

Cheers

I think I'm one of the ones with a troublesome line, only getting about 42 Meg on a 450 meter line, with interleaving at 700. my connection has not resynced for just over 500 hours now, so will be interesting to see if it improves when it gets to 4 weeks.

I was the first on my cabinet, but my attainable rate has not reduced much at all, perhaps due to an underlying fault.

Is my connection worth it, yes absolutely!

Personally I do see DLM as a hack, I dont see it as a standard part of the VDSL tech, I may be wrong but I guess its some sort of external script thats run checking errors etc.

DLM been over agressive is one issue especially when forcing interleaving, I would rather have a higher snrm (rate cap) than higher base latency. All I can say based on my adsl days the relief I got from losing DLM was unreal, yes my line was horrific but its horrific lines where DLM is supposed to be most beneficial in my case it wasnt.

A end user can be their own version of DLM they can time a resync to when their line is at its worst which in affect reduces the sync rate and increases reliability. A modem might even resync itself during high periods of noise.

So personally I agree with tommy45 in that DLM is an abonimation. Maybe my opinion will change after I have FTTC up and running, time will tell.

As for the slow recovery back to fast path or higher sync rate after a downward DLM, thats at least a good thing otherwise there would be potential flip flopping every night between fast path and interleaving.

Edited by Chrysalis (Wed 28-Nov-12 14:50:37)

In reply to a post by WWWombat:

Who is the "they" that this is in favour of?

BTgroup
ISP's The end user should be given a choice to use DLM or not,After all they are the bill payer /customer,if that still means anything these days

In reply to a post by WWWombat:

The advantage of cabinet-based FTTC here is that it automatically reduces the amount of line that needs to be trouble-shooted to find the problem. The means it ought to be easier to locate than with an exchange-based solution... provided you can get an engineer onto the problem in the first place.

Here lies the problem, If your Dside pair is being subjected to electrical induction at one or several points in between the NTE and the FFTC cab then FTTC will probably suffer more so than what adsl2+ does, With my line i know there is such induction occurring due to the hum on the ptsn side,
I had an SFI engineer tell me what was causing it,

which i would say is able to impact the connection at times,when i asked about that sorted out,he told me very doubtful as it would take too much time & effort (cost them too much money) and that there could be more than one location involved

But i would be very reluctant to go for FTTC as the min term is 12-18mths depending on isp, there are also install charges of £50-£100 So it would have the potential to be both costly and a year or more of DLM hell ,unable to play FPS games properly online without lag or be able to speak using voice coms without having the echo effect ,
I could not bear that, regardless of it being a lot faster & possibly cheaper than my Dsl connection
But as you said or implied it's openreach that's holding things back by the way that they like to run things, but because it's a product (DLM sold with it) it does kind of kill any advances made by it

In reply to a post by WWWombat:

why blame the advanced tech of FTTC when the issue you have is with the planning & operational rules of a telcom company?

In reply to a post by tommy45:

But i would be very reluctant to go for FTTC as the min term is 12-18mths depending on isp, there are also install charges of £50-£100 So it would have the potential to be both costly and a year or more of DLM hell ,unable to play FPS games properly online without lag or be able to speak using voice coms without having the echo effect ,
I could not bear that, regardless of it being a lot faster & possibly cheaper than my Dsl connection

I've had some quite high levels of interleaving, but never had a problem playing Crysis 2, ping is always lower than ADSL, current ping on speedtests is about 20Ms with interleaving level of 700, ping on ADSL was around 50 IIRC.

Well, using adsl my ping to most servers in the uk ranges from13ms upwards, fastpath, if interleaved that can be 30-40ms , The people i typically connect up with are overseas europe and the usa, so any increase in latency would make the game unplayable, Online gaming is probably the main reason i even have an internet connection, On the latency side of things i know that your location within the uk can/does affect your base latency, then you have the Isp's routing and peering playing a part also
The thing with the is that according to the sfi engineer I'm probably only around 300m-350m from the cab , so would see near the full 80/20 if not the max

In reply to a post by BerruccI:

Does anyone know if a regrade to a 40/10 service from the 80/20 forces a DLM reset

It does. Even a regrade of the upstream alone (say 40/2 to 40/10) forces a reset of DLM.

In reply to a post by R0NSKI:

I think I'm one of the ones with a troublesome line, only getting about 42 Meg on a 450 meter line, with interleaving at 700. my connection has not resynced for just over 500 hours now, so will be interesting to see if it improves when it gets to 4 weeks.

My first line was quite troublesome - 500 metres, and DLM dropped sync to 36Mbps because of errors, on an 8a profile.

I never managed to get stats from the modem on that profile, and when the cabinet was upgraded to the 17a profile, the sync recovered back to 40Mbps - presumably due to the re-organisation of up & downstream frequencies. The attainable speed was given as 60Mbps, but we left before full 80/20 services became available.

On the stats output, I can now see that it had interleaving & FEC stats of:

R: 16 16
D: 701 1
N: 74 240
INP: 3.00 0.00
delay: 8.00 0.00

So 22% overhead.

In reply to a post by R0NSKI:

I was the first on my cabinet, but my attainable rate has not reduced much at all, perhaps due to an underlying fault.

We had a hold up with our order, so got delayed. In that time our neighbour had theirs installed, so I suspect I was suffering from crosstalk there from day 1.

In reply to a post by R0NSKI:

Is my connection worth it, yes absolutely!

I agree. I was a bit disappointed to see 40Mbps on day 1, then lose 4Mbps on day 3. But the 36Mbps was still well worthwhile.

In the new house, the speed of 80Mbps over ADSL2+ speeds of 5Mbps were even better. I keep hoping that the neighbours don't cotton on to the fact that it is better performance than VM.

In reply to a post by Chrysalis:

Personally I do see DLM as a hack, I dont see it as a standard part of the VDSL tech, I may be wrong but I guess its some sort of external script thats run checking errors etc.

DLM - or the more common name for the technology "Dynamic Spectrum Management" (DSM) - covers a fair number of bits of technology.

The need for DSM stems from the fact that every broadband user also causes interference with every other user - to a greater or lesser extent. The overall aim of all these bits of technology is to make everyone "play nice" - to make sure that no-one suffers too much from the interference caused by another user, and to share nicely.

The parts we see include
- The DLM component we know & discuss on here
- The use of upstream power backoff, to reduce the power of other users' modems.
- The use of PSD (Power Spectral Density) maps in the cabinet, to limit the interference with exchange-based ADSL
- Vectoring, to dynamically adapt to other users' interference

The DLM system we know today isn't *within* the VDSL2 specification - it sits at a level higher than VDSL2. However, the VDSL2 spec *does* define the configuration properties that it makes use of (such as the INP and delay parameters)... and DLM is the process that works out what values those configuration properties should take.

Today's DLM will indeed be performed outside the cabinet - whether scripts or proper programs are involved is irrelevent. The more complex forms of DSM will need to be done within the cabinet, eventually reaching the (natural) complexity that requires the steps be performed in hardware, not software.

These procedures *are*, however, standardised. Ofcom's NICC have a 2010 Report on DSM methods in the UK, which gives more details of the art 2 years ago.

There are also other reports linked on this page from a previous discussion.

Very much *not* a hack. Very much thought out - even if never appreciated.

DLM been over agressive is one issue especially when forcing interleaving, I would rather have a higher snrm (rate cap) than higher base latency. All I can say based on my adsl days the relief I got from losing DLM was unreal, yes my line was horrific but its horrific lines where DLM is supposed to be most beneficial in my case it wasnt.

I agree - DLM shouldn't be used as a substitute for fixing dire lines.

And interestingly, that NICC document recommends that DLM should be introduced on DSL systems that don't have it, and those that already employ the "Automated margin Adjustment" type (that gave you problems) should be upgraded to use a "Tiered Rate Adaption" style instead. The TRA style is the one currently employed in BT's FTTC.

Finally, it seems strange that Openreach's product *do* offer their customer a choice of DLM behaviours - between "standard", "stable", and "speed". It isn't obvious why the ISPs themselves can't make use of this - do BT Wholesale prevent access to this?

So personally I agree with tommy45 in that DLM is an abonimation. Maybe my opinion will change after I have FTTC up and running, time will tell.

I agree that there are some aspects of the implementation that, er, leave scope for improvement.

Here's hoping that the vectoring technology does what it says on the tin. That's the one that does away with the current "simple" level of DLM.

As for the slow recovery back to fast path or higher sync rate after a downward DLM, thats at least a good thing otherwise there would be potential flip flopping every night between fast path and interleaving.

My old line, with interleaving enabled, would not flip-flop back to fastpath.

I just check 2 sets of old stats:
- First showed 183 CRC over 3.5 days, but 3.1 million FECs
- Second showed 52 CRC over 3 days, but 2.1 million FECs

Those levels of CRC would probably trigger DLM to drop me back to fastpath, if DLM looked at those alone. It must be looking at the level of FEC to prevent me dropping back inadvertently.

In reply to a post by tommy45:

BTgroup
ISP's The end user should be given a choice to use DLM or not,After all they are the bill payer /customer,if that still means anything these days

I thought that would be your answer.

The problem is that part of the reason for DLM is to "share nicely" with everyone else - after all, if you wanted to have no errors on *your* line, all you'd need to do is whack up the power. Everyone else might have to resort to pigeons, but you'd be OK, right?

However, as I answered Chrysalis, Openreach do have a way for you to set the grade of DLM you want - to Standard, Stable or Speed. It isn't clear why ISPs don't have this option (or don't let you know they do).

And, while I do think that DLM is necessary, I agree that the implementation hasn't always resulted in the best results for everyone. Particularly when BT's "IP profile" mechanisms get in the way.

Here lies the problem, If your Dside pair is being subjected to electrical induction at one or several points in between the NTE and the FFTC cab then FTTC will probably suffer more so than what adsl2+ does,

Why do you say that? I'm not sure that it's a given that FTTC will probably suffer more - it very much depends on the nature of the interference and its location

If the cabinet is notable closer to your house than the exchange, the signal level will be higher when it arrives (except for the portion that get deliberately crippled by the cabinet's PSD mask). That higher signal level might make all the difference.

With my line i know there is such induction occurring due to the hum on the ptsn side,
I had an SFI engineer tell me what was causing it,

which i would say is able to impact the connection at times,when i asked about that sorted out,he told me very doubtful as it would take too much time & effort (cost them too much money) and that there could be more than one location involved

Does the SFI engineer know where the suspected location is?

But i would be very reluctant to go for FTTC as the min term is 12-18mths depending on isp, there are also install charges of £50-£100 So it would have the potential to be both costly and a year or more of DLM hell ,unable to play FPS games properly online without lag or be able to speak using voice coms without having the echo effect ,
I could not bear that, regardless of it being a lot faster & possibly cheaper than my Dsl connection

Ah, I can agree it is very off-putting to see contracts like that. What is your current solution to get around all those problems?

And what kind of latency can you accept, and still have functioning games & voice? Or should i ask the other way around - what was happenign to your latency when it was all going wrong?