dslam problem?

hello all. hoping someone may have an idea what is happening with my vdsl2 . when installed i sync at a good 72 minimum but over the last two years this has now dropped to 52 (handback is 67)zen have been sending openreach engineers to check the line but find it is perfect condition and could not understand the loss, after 2 visits engineer rang and told me there was some kind of error with the card or config on the line? and it would not go above that speed. he did not know what to do and would escalate to another team, two days later he rang back to say they where about to change card and if that did not work nothing they could do. alas i lost 2 more meg on the change

Dropping from 72Mb to 52Mb is very consistent with crosstalk.
Crosstalk is simply interference caused by other lines on the DSLAM.

Pretty much every single VDSL2 line loses some speed over time as their cabinet fills up.
The early adopters will have lost the most.

There's possibly no error at all.

Unless you're lucky enough to have a BDUK funded cabinet that's got vectoring.

In reply to a post by Grimers:

Unless you're lucky enough to have a BDUK funded cabinet that's got vectoring.

Indeed, but even lines with Vectoring lose some sync speed over time.
Vectoring attempts to mitigate the effect of crosstalk but it doesn't cancel it out completely.

OpenReach's deployment of Vectoring is not exactly efficient (that's being polite).

Their free for all on what modems are used on the VDSL DSLAM's makes things even worse with many modems (including some modems supplied by big ISP's) not supporting Vectoring.
Many of them aren't even Vectoring friendly**

A customer on a cabinet with Vectoring with a modem that fully supports Vectoring can still lose 10-20Mb off their sync speed from a single rogue modem that doesn't support Vectoring.

If any of the BDUK cabinets with Vectoring reach their capacity and need a 2nd cabinet (or VDSL Sidepod) installed, the 2nd DSLAM does not support Vectoring.
Considering the Huawei DSLAM's support Node Level Vectoring (Vectoring across multiple DSLAM's) it's a poor deployment on the part of OpenReach.
Every single line connected to the 2nd DSLAM can cause crosstalk on lines connected to the Vectoring DSLAM.

Taking all that into account and the very small amount of cabinets that actually support Vectoring, there's a high chance that most drops in sync speed over time are due to crosstalk.

Whether that's the case for the OP's line or not we can't say, but it's a strong possibility.

**Vectoring friendly is when a modem doesn't mitigate crosstalk on an end users line, but still supplies the Vectoring group (the DSLAM) with the info necessary to help cancel crosstalk on other lines.

I see. Thanks as always for your detailed explanations John, it's greatly appreciated.

thankyou for your full description of what may be happening, i did not think you could lose so much speed from crosstalk, one question if i may, i am considering going to 300mb gfast, would i have the same problem there or is the routing/technology separate from vdsl

What does the BT Broadband Availability Checker show for your address?
Does it even show G.Fast as a possibility in your estimates?

https://www.broadbandchecker.btwholesale.com/#/ADSL/...

G.Fast has a very short range, much shorter than VDSL2.
Usually if you aren't close enough to the cabinet to receive the full 80Mb (or very close to 80Mb) then you aren't close enough for G.Fast.

With your current sync I would be very very surprised if you could order G.Fast.

G.Fast has Vectoring like VDSL2, but it is mandatory.
It is much better deployed than on VDSL2.

i am 80 meters from cabinet, checker shows 71 expected on vdsl2 , i can order gfast 300 expected 245, but will i have same problem

have just run the test to update
vdsl clean 80m
vdsl impacted 80 meg
gfast clean 330
gfast impacted 328

G.fast requires vectoring to function, so if your issues are being caused by crosstalk (it sounds like they are), then moving to G.fast will help.

Your choice of ISPs becomes quite limited, though the big players are all there.

In reply to a post by buck009:

i am 80 meters from cabinet, checker shows 71 expected on vdsl2 , i can order gfast 300 expected 245, but will i have same problem

Go for G.fast please! It very good and more higher speed than VDSL2 because G.fast got Vectoring on it. You will get 330/50 easy as you saying u are within 80m away from the cabinet. You are more likely to stay above 330/50 for a very long time! Never drop.

I am connected to G.fast 160/29 but the line max is 210/29. I am about 280m to 300m from the cabinet. G.fast have two products either of your choice 160/30 or 330/50.

Edited by adslmax (Tue 01-Jun-21 23:15:33)

In reply to a post by buck009:

i am 80 meters from cabinet, checker shows 71 expected on vdsl2 , i can order gfast 300 expected 245, but will i have same problem

Your estimates are good, and your line is well below the handback threshold.
The low sync may not just be crosstalk.
The checker certainly seems to think you should sync higher and it takes crosstalk into account.

If there is a line issue causing low sync then that would be carried over to G.Fast.

If it is entirely due to crosstalk that you're syncing so low on VDSL2 then switching to G.Fast will definitely help.
There's 300-400 active VDSL2 lines on many cabinets (over 550 on mine), usually with no Vectoring.
The G.Fast DSLAM's are much smaller and take up is low. It has Vectoring (it's mandatory on G.Fast) so crosstalk would be less of an issue.

As you're below the handback threshold your ISP should be willing to send OpenReach to check your wiring and try improve the sync speed.
They've done that with no success it seems.
If the current low speed issue is the DSLAM ports or the line card then G.Fast would bypass these issues.

Edited by j0hn83 (Wed 02-Jun-21 01:22:42)

Here’s another vote for g.Fast … I’m 140m from the cab, and get a 330/50 sync with a theoretical max of around 400.

A nice low ping … it’s all good for me

Here’s a cheap and dirty speedtest over wifi to my iPhone XR ….. the router is two floors below

Edited by Zarjaz (Fri 04-Jun-21 08:25:10)

In reply to a post by buck009:

i am 80 meters from cabinet, checker shows 71 expected on vdsl2 , i can order gfast 300 expected 245, but will i have same problem

The estimates only guessed. Your line can easily get 330/50 with max line maybe over 500/90 pretty very easy with that short distance to the cabinet 80m away. The bloke is 140m away and got 330/50 (max line 400/70) and I am 280-300m away and I get 160/30 (max line is 210/30)

In reply to a post by Grimers:

Unless you're lucky enough to have a BDUK funded cabinet that's got vectoring.

Or you're just lucky. My speed has improved over the last couple of years and for a while last year was nearly back up to full speed. It's fallen back a little now but it's still faster than it was two years ago. Maybe one of my neighbours has cancelled their service.

Some cabs they replaced the original tie cable with cat5 grade cable to reduce the effects of crosstalk.
Some of the originals tie cables were not terminated correctly or the strips were damaged or crack over time and many have been replaced/ reterminated.

thankyou all for your comments, this has today been sorted, my isp "zen" booked a third engineer visit, surprising he reported back no error found but interestingly i am now syncing at 75 meg RESULT

That's good to hear it but what if the problem come back again? Then go for G.fast instead.

Comes down the same copper from the cabinet max.

Yes I know that. But I do think the engineer haven't fix his line because more likely resetted DLM back to 75meg but it probably will reduced again if cross talk still issues as g fast does not affect by any crosstalk

Good point.

(Though just far less cross-talk. I don't think "none" is guaranteed).

as an update now two weeks on still sync at 75 /20 only change i have seen is snr changed from 6 to 5

In reply to a post by buck009:

as an update now two weeks on still sync at 75 /20 only change i have seen is snr changed from 6 to 5

It will take 1dB step per day eg: 6dB to 5dB, 5dB to 4dB and then final step 4dB to 3dB to get your sync rate at nearer max rate of 80Mbps.

If the SNRM has changed from 6 to 5 with no change of sync, that is due to noise. Not a DLM change.

It took nearly 4 months for my SNR to reduce from 6db to 3db when I was on FTTC.