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[ColinS]

So the combinations are:

• 36 transmission rate bands (an extendable? range of max and min down- and upstream rates);
• 3 choices of maximum interleaved-delay (no=0ms, low=8ms and high=16ms) in the downstream;
• 2 levels of max interleaved-delay (0ms and 8ms) in the upstream; and
• 7 levels of INP protection (from no protection to 10 symbols)

What I'm wondering  is whether ATM they are only really using (some) of the first in the DLM, and none of the rest, and that is possibly the change that a lot of people are reporting.  So as BE says, he has seen different interleaving depths in the past, but all of a sudden he's on fastpath but with a restrictive banding?

[Bald_Eagle1]

I don't have my current Profile Name from Plusnet, but this is how they reported it at one point - before the physical line problems were finally repaired during May 2012:-

Profile Name   13.7M-27.4M Downstream, Interleaving High - 0.128M-0.8M Upstream, Interleaving On
Time Stamp    2011-07-28T12:44:35

It would perhaps have been more helpful if the engineer had mentioned my PROFILE band rather than sync speed at the cabinet.

Plusnet did disclose your channel-profile in so many words.  There are just a couple of channel-profile parameters absent from its report:  the exact interleaving delays, down and up, and the INP levels, down and up (and the reserved transmission rates).

The example I cited was from before we had access to unlocked modems & their secrets.
I must have some more from when I was able to log my stats & will post an example or two if I can track any down.


I'll also ask Plusnet if they still have any record of the Profile Name from when my connection could sync at around 30Mb, just to see if it was something like a 15M-30M Profile i.e. my connection was performing very close to the top end of the banded profile.

Maybe it was a 20M-40M Profile & the speed loss over 100m to 1300m line length brought it down to 30Mb at my home.

The low upstream max of 0.8M was for a short period of particularly poor performance/faults.
At that time it was an 'up to' 40/2 service.
Nowadays it is an 'up to' 40/10 service.

Unless your D-side was zero centimetres long, the sync speed measured at home will always be lower than the sync speed measured at the cabinet, with one big caveat. 

The only time that the sync speed at home will match the speed at the cabinet is when it has hit the maximum transmission rate/s defined in the channel-profile.

If the sync speeds would otherwise exceed those maximums then the line will be banded or capped to those maximum rates (e.g. 27400/13700 in your case).

And that is the circumstance when the speeds measured at home are identical to those measured at the cabinet, as per the engineers' note from Openreach, posted by BlackSheep.

That's what I thought it should be.

Perhaps the Openreach note was somewhat ambigous in its wording.
It certainly caused a little head/fur scratching at the time 

[ColinS]

Maybe it was a 20M-40M Profile & the speed loss over 100m to 1300m line length brought it down to 30Mb at my home.

I think getting and understanding that is part of the key here.  On the one the quoted to me today for my line, you can see that I am clearly maxing out their banding, and frankly would probably also max out a 67-80Mb band too, so why won't the DLM back off to that?  I can't see anything to prevent it? Not now anyway.    However, it is certainly coincidental if not suspicious that that banding is closer to their 69Mb prediction rather than the reality. 

[ryant704]

Just for info ......... there are 36 levels of banding that can be applied by Rambo, from 0.125Kbps up to 80Meg.
The same system has three levels of Interleaving shown to us a '1'- No Interleaving, '1'- Low Interleaving, '1'- High Interleaving.

That seems to correspond to something I've seen elsewhere, where (it is said) that the ISP can request on behalf of the EU one of 3 VDSL profiles Gaming (No interleaving?), Standard (Low), and Stable(High). 

That sounds like the 3 Default DLM profiles which are Standard, Stable and Speed.

Source: http://www.openreach.co.uk/orpg/home/products/super-fastfibreaccess/fibretothecabinet/fttc/downloads/GEA_FTTC_4.pdf

[ColinS]

Yep Ryan, I think it was you I was referencing!    Thanks for the info. 

[Black Sheep]

there are 36 levels of banding that can be applied by Rambo, from 0.125Kbps up to 80Meg.

You must be refering to DS then? Are these tabulated anywhere (like here in Kitz perhaps? ) in a form like the ones quoted by PlusNet?  Does every DS band have a fixed corresponding US band?  If not, are we talking 36 DS x ?? US combinations? 

Colin, the US has 18 levels of banding, but just the 2 Interleave functions ........... 'Interleaving On', and , 'Interleaving Off'.

[Chrysalis]

Working on VDSL is as the 'briefing' laid out stipulates. On a fault free circuit, you could have 10Meg at the EU's premises. If you then went to the DP or an Underground Joint, or the actual Cabinet, you would still see 10Meg.

An engineer visited today to 'investigate' my current speed having reduced to more than 25% less than my estimated speed.

He told me that DS speed is 27Mb at the cabinet yet his Exfo reported only 18845/5449 Kbps at my master socket.
He said that was normal & due to it travelling around 1300m from the cabinet & that sync speed at my home looked about right for a line of that length.

My HG612 was reporting sync speeds of 20764/4859 Kbps immediately before he unplugged it to plug in his Exfo.

Just before he left, my HG612 connected & reported sync speeds of 20667/4774 Kbps.


Could the engineer have been mistaken or does this suggest the line isn't actually as error-free as his PQT & Eclipse tests suggest?

When I also mentioned that Interleaving had recently been unexpectedly turned off, he said that's how VDSL2 connections always run i.e. on Fastpath.

Hmmm.........................................

question how can a cabinet only get 27mbit sync? its a effective 0m length? or at least the length between PCP and FTTC cab.  Or is the line banded at 27mbit?

[Chrysalis]

[EDIT] Chrysalis observed earlier in the thread

What are you speaking of is probably line banding which the new DLM does instead of adjusting target noise margins (I assume so it cant be overriden by people tweaking the noise margin CPE side).

To some extent I believe that this is so, but not entirely, as BE has also had fastpath removed.  But is that a temporary or a permanent change e.g. have BTOR updated the profiles recently?  I don't know but it is suspicious.

Simply using banded profiles with max sync rates like that is a very crude way of managing line conditions, but if they were doing that it might explain some things we are seeing e.g. reduced profile maxes while DLM still apparrently believes there is no need for either interleaving or INP.

The cynic in me wonders if BTOR are quietly banding everyone at the next nearest profile to the official BTOR 'Estimate'? 

Ironically its a way to claw out of BT infinity contract without penalty.

BT state "We wont slow you down"

Banding does exactly that. (interleaving does also).  i have already tested it, I was given a copout of my contract simply because DLM "slowed me down".  If they had to keep it legal, then everyone would have a max banded profile, interleaving would probably have to be able to be reset on user request also.

[ryant704]

The DLM can only sync to maximum rate of the band that has been applied (This is what the NGA Helpdesk told the engineer). My line had a profile assigned called TR03 (301) which was incorrect for my line, it was then applying a 7Mbps - 19Mbps band. It would keep syncing to the exact same sync (19Mbps with a 18.42 bRAS Profile) and band after full DLM resets, this went on for around 2 months. The NGA helpdesk then said it assigned a different profile (Shame they didn't tell me the name, was Kevin from BT care that did before and I was moved on to the ELC Team), the 7Mbps - 19Mbps band was no longer being used. This leading to my speed returning to the 25/27Mbps mark. Though 2 days later a 15Mbps cap was applied to my line from Wholesale... that's going off-topic though!

[EDIT] Chrysalis observed earlier in the thread

What are you speaking of is probably line banding which the new DLM does instead of adjusting target noise margins (I assume so it cant be overriden by people tweaking the noise margin CPE side).

To some extent I believe that this is so, but not entirely, as BE has also had fastpath removed.  But is that a temporary or a permanent change e.g. have BTOR updated the profiles recently?  I don't know but it is suspicious.

Simply using banded profiles with max sync rates like that is a very crude way of managing line conditions, but if they were doing that it might explain some things we are seeing e.g. reduced profile maxes while DLM still apparrently believes there is no need for either interleaving or INP.

The cynic in me wonders if BTOR are quietly banding everyone at the next nearest profile to the official BTOR 'Estimate'? 

Ironically its a way to claw out of BT infinity contract without penalty.

BT state "We wont slow you down"

Banding does exactly that. (interleaving does also).  i have already tested it, I was given a copout of my contract simply because DLM "slowed me down".  If they had to keep it legal, then everyone would have a max banded profile, interleaving would probably have to be able to be reset on user request also.

I've always agreed on this, I've asked BT this question. Here is the response (partly)...

"As you’ve mentioned, we can change the preference between Standard, Stable and Speed but in practice this will have little impact on the sync rate."

Then when the engineer was talking to the NGA helpdesk I got him to ask a couple of questions for me on the DLM (he was interested as well). He said there are many profiles that ISP use, none uses the default ones offered by Openreach, each ISP modifies the ones that Openreach offer though the default ones from Openreach will do exactly as they sound. He then mentioned you could see a speed difference of around 5Mbps if you're on the Speed profile instead of the Stable profile (note he wasn't talking about my line).

He then proceeded to talk on about Crosstalk, he stated if all people were on the "Speed" profile the service would degrade to a slower standard than if it was on a managed service. He said because everyone would be on "FastPath" there would be a higher number of errors this leading to more crosstalk? (First I've ever heard of this, I'm not sure if it's true as it wouldn't be the first time I've been lied to). Then proceeds to tell me that this would degrade the service to a slower rate if it wasn't managed the way it is.

[ColinS]

question how can a cabinet only get 27mbit sync? its a effective 0m length? or at least the length between PCP and FTTC cab.  Or is the line banded at 27mbit?

Of course it's banded (i.e. a profile with max/min sync rates has been applied by DLM)

To paraphrase Asbokid:

The only time that the sync speed at home will match the speed at the cabinet is when it has hit the maximum transmission rate/s defined in the channel-profile.

If the sync speeds would otherwise exceed those maximums then the line will be banded or capped to those maximum rates.

And that is the circumstance when the speeds measured at home are identical to those measured at the cabinet, as per the engineers' note from Openreach.
 

[ColinS]

There is more discussion around profiles and DLM here http://forum.kitz.co.uk/index.php/topic,12535.0.html

Asbokid has also listed references to BT's DLM patents (as originally discovered by 7LM) here http://forums.thinkbroadband.com/fibre/4240841-dlm-fault-recovery.html?page=1#Post4240966

It is likely that the framework described therein has not changed substantially, but the contents of the profiles used would certainly seem to have been altered to use sync rate banding rather than SNRm (for example) as the means of controlling the stability of the line.

Ryan, FYI, it describes:
a) how differing error rates might be applied to the 3 EU requested stability levels you cited, and
b) how the requested stability level affects the manner and time-frame over which DLM steps the profiles down and back up again in the light of changing line conditions (or at least, how it ought to do that)!

[waltergmw]

@ Colin,

Here is one we prepared earlier (Thanks as usual to to Eagles, pussies and naughty children !)

A newly commissioned service under 200 m from the FTTC had a sync speed of 90.41 Mbps on 15 January 2013 but after the training period it adjusted to the channel profile and is now 79.997 Mbps.
Oh what a lucky chap !

Kind regards,
Walter

[ColinS]

@ Colin,

Here is one we prepared earlier (Thanks as usual to to Eagles, pussies and naughty children !)

A newly commissioned service under 200 m from the FTTC had a sync speed of 90.41 Mbps on 15 January 2013 but after the training period it adjusted to the channel profile and is now 79.997 Mbps.
Oh what a lucky chap !

Yes, I remember it well.  So was mine until somebody fidgetted around in the cabinet on 08/04/2013. 

[waltergmw]

@ Colin,

You're not the only one !

http://www.ewhurst-broadband.org.uk/?p=3528&cpage=1#comment-730

Kind regards,
Walter

[ColinS]

You're not the only one !

http://www.ewhurst-broadband.org.uk/?p=3528&cpage=1#comment-730

No doubt, but what has happened to me and others is not remotely similar to that report (other than experiencing a reduction).  There was no progressive reduction over time, just the immediate application of a lower banded profile in the face of a transient disturbance to the line.

IMO in my case it has nothing at all to do with FEXT or DPBO.  It is just a flaw in DLM which, for reasons we would all like to know, is simply refusing to back off on a perfectly respectable line with a BER currently estimated between 5*10^-11 and 2*10^-8, either of which are way above the alleged 10^-7 BER of a good line.

In other words, the profile is 'stuck' maxing out the profile max sync, while still only on an RCO of 73%.  It appears that both BlackSheep and Ryant704 were also stuck until their lines were reset, when their sync rose to the level their lines were capable of.  IMO, no one should be stuck on a profile which they max out, other than the current 80/20 exception.

While the product is sold as 80/20, I don't have any argument with a profile banding that results in a 79.997 actual sync on those lines that are capable of it.