Poor sync speeds with ADSL2+

[joll200x]

Well, I think the whole WBC / 21CN / ADSL2+ 'upgrade' has to be the most disappointing development in broadband yet.
The latest disappointment being my line dropping to speeds a good meg or so lower than it was with standard ADSL. The irony in this is that I've done quite a bit of tidying up of my internal wiring and wiring my modem into the back of the master socket with CAT5 cable to improve my speeds! bah...

Does anyone know of any problems which might be causing this - other than the usual cr*ppy quality lines to the exchange? I've tried to report a fault through support as the speed has dropped significantly and I was pretty much shunned. Should I contact support and simply request a fault is logged with BT wholesale? I read on another forum something about reporting a fault to BT relating to intermittent cross-talk on the voice side which would result in being switched to a different piece of copper?

Really any suggestions would be great as at the moment I'm thinking my only option likely to yield any success is moving to an ISP who is offering LLU?

Thanks,

Stu

[rireed3]

can you post the following stats from your router?

Down connection rate
Down noise (SNR) margin
attenuation
time connected on current sync, sometimes called WAN uptime

These errors:
FEC
CRC
and error seconds

Richard

[joll200x]

       Line Rate       TX: 774 Kbps ,RX: 3043 Kbps
      ADSL Firmware       SW2.0.11a
      ADSL Firmware [Backup]       SW2.0.11a
RF status
   
Local   Remote
Tx Power   12.4 dB   20.5 dB
SNR Margin   15.0 dB   6.5 dB
Line Attenuation   53.0 dB   31.5 dB
Statistics
   
Receive   Transmit
Packets   989258   764306
   Errors   27   0
   Dropped   27   0
   Overruns   0   0
   Frame/Carrier   32   0

believe it or not, my so-called enterprise firewall doesn't give me the actual SNR - just the margine. Line uptime is about 5 hours since I forced a re-sync earlier.

[rireed3]

Good information.

First, avoid any more re-syncs.  BT have punished your line for instability.  To explain, I'll have to explain "noise margin", also called SNR margin.  No routers I know of show the actual SNR.

SNR margin is extra SNR above some 'floor' that can be used to encode bits.  In other words there is a low SNR below which no useful information can be sent.  The margin above that shown by the reception at both ends is called noise margin, or SNR margin.

BT normally sets a target somewhat higher that the noise 'floor' below which it won't code any more bits.  This keeps the encoded bits somewhat away from changes in the noise.  Normally that 'target noise margin' is 6db.  BT has an automatic system called Dynamic Line Management (DLM) that monitors your line for errors and re-syncs, maybe other things I don't know about.  DLM has raised your target noise margin to 15 db partly because of too many re-syncs.  That has cut your speed by at least 1 Mbps, but your problem may not be solved by getting target noise margin reduced.

Assuming those 27 errors keep growing, and weren't from one big lightning strike, you are now getting about 5 CRCs per hour, which would be fine, execpt that if your target noise margin went back to 6 db, you'd get tons more, and you might keep losing sync, and that instability would just cause DLM to raise the margin back to 15 db.

If the 27 errors are _not_ growing, that's the best news, because it means the line is fairly noise-free and the re-syncs were due to something else, maybe hot-unplugging the ADSL line.  If you've never asked before, IDNet support may be able to get BT to set your target noise margin back to 6 db.  BT won't do it twice, so make sure you're not getting growing errors or fluctuations in noise margin with >4 db between highest and lowest.  If BT is unfair, you can only wait 14 days for DLM to decide it has made a mistake and start cutting your target margin 3db at a time.

Otherwise, there really is extra noise on your line.  If it's BT's noise, they won't fix it without an act of Parliament, so first you must be absolutely certain your end is clean.  Using the test socket is the best way, so you have pulled away the lower half of the face-plate and plugged your microfilter for the router straight into the BT socket underneath, as I understand.  You can see that the wires to the rest of your house phones are connected to the now-dangling faceplate, so the router-with-microfilter is connected directly to BT's line, and there is nothing else at all wired to the line.

The only other things under your control are

• the length of your cables (ADSL cable should be _short_, even if CAT5), including cables to phone devices, and
• electrical interference in your house that can affect the router power supply as well as the cables.

Also, power cables should not be parallel to the ADSL cable as much as possible.

If all that has been taken care of, have a long quiet conversation with support.  You have probably been moved to different line equipment, and that may have affected your line.  It's possible that a different router would do better.  In the end, BT won't budge over a loss of 1 Mbps, and that's why you felt shunned.  There is a figure called Fault Threshold Rate, 70% of the lowest sync in your original training period.  Above that, BT says you don't have a problem.

It is possible that there is a voice problem you can identify to BT.  There has to be pretty loud clicking or scratching so you can complain about disrupted converstaion.  If that's what's happening, getting the voice fault fixed will likely get the broadband speed back.

Richard

[Ann]

Or you may have the typical problem that some others of us have had when changing over to +2.  I had an SNR Margin of 12 or 13, sometimes it would go up to 15.  Had the same when changed to +2 with lower speeds than normal until BT kicked something and the speed went from 5 to 11 and the SNR Margin down between 4 and 6.  They also took interleaving off.  So it's worth asking IDNet again if there's something else wrong.

[rireed3]

Ann,

For comparison,

• Do you know what your CRC errors were doing -- how many per hour roughly -- before BT kicked something?
• Also before the kick, was your noise margin rising and falling -- >4db between high and low?

Thanks,
Richard

[Ann]

No sorry, I don't know what CRC errors are called in 2Wire speak.  I have nothing called exactly that listed in the logs that I can see, not that I'd remember what was what anyway.

My noise margin would go to 15 for a while then down to 11 or 12 then back up.. not quickly, it might stay at one level for a few days before changing. 

[rireed3]

You reported that your noise margin dropped to 4.8.  Is that also varying, say between 3 and 7?  I'm trying to decide if you got moved to a different line.

Thanks again,
Richard

[Ann]

It's going between 4.8 and 6.1.  While the synch rate has obviously risen the max rate has risen too.  It used to be 6 something and now it's 12641.  I thought that seemed as though they've corrected something their end.

[rireed3]

That looks like a much better physical connection. Is the attenuation the same?  If it's significantly lower, it's a different, shorter pair.

[Ann]

No, not lower.  Attenuation is slightly higher than when I was on max which I read it was supposed to be when on +2.  I have a feeliing that it only went higher after the kicking which makes me think that I wasn't on +2 at all except the upspeed had gone up before which meant I was on +2.  See the confusion.

[Rik]

Good information.

Great post, Richard. 

[rireed3]

See the confusion

I can, but I wouldn't bet on BT  

joll200x -- do you have a line in your router stats at all similar to this?

Modulation: G.992.5 annex A

[rireed3]

Great post

Cheers, Rik.  I kept trying to find things to leave out, but this stuff is so ridiculous! 

I don't blame people for not believing it when you first tell them what's going on.   

[Rik]

Sometimes, only the long answer will do, Richard.

Ever since my first modem, back in the early 80s, I've regarded comms as a black art, where the best results are achieved by a chanting circle of local witches standing around the router.

[rireed3]

 

[joll200x]

I can, but I wouldn't bet on BT  

joll200x -- do you have a line in your router stats at all similar to this?

Modulation: G.992.5 annex A

firstly thanks for that monster post

I don't have that exact line in the stats - but the ADSL mode is set to ADSL2+. I do have the options for ADSL2+,g.dmt,g.lite,t1413,multimode but it's a manual choice.
The amount of CRC / frame errors have been a concern since I moved into the house about a year ago. BT wholesale came out once and made some changes (by changes - read they fiddled and kicked the cable housing where it comes into the house) and they didn't remove the errors but it reduced the speed at which they were increasing. Im not sure what else I can do to tidy up my wiring, i've already removed about 10 metres of extension cable where the previous owner thought it would be a great idea to take the extension for the upstairs 'office' across the front of the house, up the side, into the loft and then down into the office. I've chopped any other extensions into other rooms in the house so there's only an extension off the master socket for the loung (3 metres) and one going into the office (now about 1.5m of CAT5). I'm pretty certain the fault is outside of my house, i've done lots of testing with the test socket and still see the errors 
I'm off on holiday for two weeks soon so might try turning everything electrical off and unplugging the one phone in the house to see if I still get the large amount of errors.

thanks again

[Rik]

I wouldn't recommend leaving the router on while you're away. A major thunderstorm could cause a lot of damage.

[rireed3]

When you were in the test socket, did you get the same 3M sync rate and 15 db noise margin along with the same errors?

[joll200x]

yeah pretty much identical SNR margin / attenuation and sync speeds. Errors increse pretty steadily too unfortunately

[Rik]

Have you got a battery-powered MW radio? If so, de-tune it, so all you have is white noise, and then follow your phone wiring from where it enter the house to your router, listening for the noise to increase. If it does, you have a local noise source causing problems.

[joll200x]

I'm so trying this when I get home, purely for its mcguyver value

[Rik]

 

If nothing else, get someone to video your exertions and post the results on YouTube. 

[joll200x]

as daft as that sounds, i will do exactly that. after walking around the house with my shower radio and making my neighbours think not all my dogs are barking - the interference scanning did find some interesting bad spots in the house. i've since removed some electrical stuff in the house and i've had no errors since. (by removed i mean thrown in the garage, the worst offending item was a dect phone and i'd unplugged it from the phone line before but never realised how much RF interference it was kicking out just being plugged in!)

Once again, thanks rireed3 for the tip on the AM radio!

Ever since my first modem, back in the early 80s, I've regarded comms as a black art, where the best results are achieved by a chanting circle of local witches standing around the router.

Couldn't agree more!! Much prefer the LAN side where there is far less voodoo involved

[rireed3]

Once again, thanks rireed3 for the tip on the AM radio!

Cheers, but that was Rik