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Long Line and possible interference issue

bogmonster
Newbie
Posts: 7
Registered: 06-01-2015

Long Line and possible interference issue

Hi,
I am soon to be migrated to Plusnet from BT but need to get a fault fixed first which looks like it might be a line card in the exchange. Anyway, whilst that is going on I think it makes sense to try and resolve any other pinch points I have. I am on a long line, at a guess maybe 7km (it is 4.9 as the crow flies). Attenuation is ok I think at 58bB down and 35bD up. The internal wiring is not the best. There is a long and largely unnecessary internal run to the master socket in non-twisted cable. Also a non-twisted cable to the router.  I might see if I can get all the slack (about 10m) cable removed. Obviously the shorter the connecting cable the better but I wanted to know how effective cat5e based rj11 cables are or should I move the router as close to the socket as possible and use a 2m cable?
I need to have a proper investigation but I suspect REIN is causing a fair sized issue. Just bought a new router (Broadcom chipset) and installed routerstats but have yet to investigate the results. A very early indication suggests the central heating might be a problem – this is an old oil fired affair but I suspect it is actually the water pump. The boiler is properly bonded to an earth spike. Its not street lights, there ain't one of them for miles thank god.
I am sure there are other sources of interference in the house - my workshop is close and has lots of machine tools and my wife's glass studio is also close with big extractor fans and an electric kiln. However, these probably don't get used enough to cause too much of an issue.
I plan to do the rounds with a MW radio to see if I can pick anything up - just need to find an analogue radio.....
Does this sound like I am on the right track – what else should I be doing?
BW BM.
9 REPLIES
Plusnet Staff
Plusnet Staff
Posts: 1,834
Thanks: 3
Registered: 24-07-2014

Re: Long Line and possible interference issue

You're off to a good start by the sounds of it. If you can identify the source, and it's in your remit, that's brilliant and saves you having BT investigate for you (that can take a long time).
 Tony
 Plusnet Support
bogmonster
Newbie
Posts: 7
Registered: 06-01-2015

Re: Long Line and possible interference issue

Thanks.
I think there is definitely a problem at the BT exchange - OR engineer coming out Friday. Hopefully they can fix it. I will ask the engineer if he will remove the extra cable internally as well, it is the wrong side of the master socket for me to do even if it is only two wires..... I will more the router right next to the master socket.
Using the new router is definitely helping reduce errors. My target SNRM has been reduced to 6 from 12. With an SNRM of about 6 I am getting about one ES per minute, spaced out quite evenly and the line is stable (until the phone rings (that is the exchange / line problem). However my sync speed is on in the low side. From what I can see at 58.5 dB at a SNRM of 6 I should get a sync speed of about 3 Mbps whereas I am actually getting 2.6 Mbps. My IP Profile is 2.28 Mbps which 88% of my sync rate.
So, stupid question, how is the sync rate set ?  I know the DSLAM and router handshake and agree the sync rate when setting up the connection and that lower SNRM = higher sync speed. I also know that tweaking the SNRM on the router can will result in a higher sync rate (at the cost of stability).   What I don't understand is why two different routers on two different lines with the  same SNRM and attenuation will sync at different speeds? So on Kitz.co.uk I read 'During the sync process the DSLAM and router negotiate a sync speed based on the various conditions of your line, allowing "spare SNR" for normal fluctuations.' What are these various conditions other that attenuation and SNRM?  
I understand that different chip sets on the router and different exchange equipment is one factor. What about historical errors? What about SNRM at different tones?
BM
runhare
Aspiring Pro
Posts: 512
Thanks: 47
Fixes: 1
Registered: 09-10-2007

Re: Long Line and possible interference issue

Hi.. This might be your problem: (Apart from the rubbish wiring )
Tthere is a known issue  with long lines which results in the sync dropping when the phone rings. Its not due to any fault but is caused by incompatibility between the System X POTS equipment in an exchange and the Ferranti Mk2 ADSL (DSLAM ) equipment on some long lines . Simply changing  to another line card will have no effect or swapping the DSLAM but there is a fix which can be actioned at the exchange. How do I know this ? I had the same issue , phone rings, sync drops. It went on  for years, and stability and download speed  on my line was all over the place.  I had many visits from  OR engineers &  more than one line card swap,  and still  it continued. Finally last December there arrived an OR engineer who found out about this incompatibility issue and luckily was able to speak to a BT OR manager who knew the problem and the solution . Since them , perfect stability and no loss of sync !
good luck!
Also get the master socket installed as soon as you can inside your property where the line enters the house . you need an NTE5 Mk faceplate . Plug  the router directly into it . Use either wifi extender  or a Homeplug Power line system to extend your network if the location of the router is not convenient .
Community Veteran
Posts: 19,100
Thanks: 437
Fixes: 21
Registered: 31-08-2007

Re: Long Line and possible interference issue

Just for future reference to any other readers, do NOT use Homeplugs. They can be a major source of interference which can create significant drops in SNRM and resultant slower sync speeds. On a long line this will be a severe issue. This is a well known long established problem which at long last is getting some more serious attention.
See http://community.plus.net/forum/index.php/topic,135805.0.html
What is definitely needed is modern drop-wire (it's twisted pair) ideally direct to the Master socket (latest type) and ideally fitted with the Mk3 SSFP - Service Specific Filtered Plate (nick-named the vDSL plate). The Mk3 plate has an improved common-mode filter as well as the normal filtering for phones when the master socket front plate is refitted.
If you can't get the master socket installed at a convenient point for your modem/router, the best thing is to run an extension socket using CW1308 (internal twisted pair cable as used by BT). This is connected to the IDC Terminals on the MK3 Plate. Other extensions for phone usage can be connected to the front plate and are then already filtered by the Mk3 plate (it doesn't matter so much if those extensions for phones are older wiring, but ideally replace it if you can with CW130Cool.
Alternative incoming wiring installed by Openreach to a master socket could be - standard twisted pair drop-wire to an internal connection box (eg. BT77A) then CW1308 cable to the Master socket - usually done where the master is some distance from the external point of entry.
The important thing is that it is twisted pair drop-wire a round cable with a black sheath (older types can be oval cross-section or figure 8 cross-section neither of which are twisted pair) and any unfiltered internal wiring either to a master or to extension sockets for broadband is again twisted pair (CW130Cool.
The previous version twisted pair drop-wire (CW1411 otherwise known as drop-wire no:10B) had 2 pairs and 3 steel strainer wires. Recent installation now only has the one pair and steel strainer wires.
The use of twisted pair cable is essential to reduce the pickup of external interference especially MW/AM propagation which increases dusk to dawn and can cause significant reductions in SNRM and reduced sync speeds. The length of the cable is not material in this context. Disconnection of the bell-wire is also a must on unfiltered sockets.
Community Veteran
Posts: 19,100
Thanks: 437
Fixes: 21
Registered: 31-08-2007

Re: Long Line and possible interference issue

Forgot to mention in the previous post, that another possisble cause of SNRM reduction and sync drop when the phone rings can be a poor joint somewhere on the line.
runhare
Aspiring Pro
Posts: 512
Thanks: 47
Fixes: 1
Registered: 09-10-2007

Re: Long Line and possible interference issue

The engineer that visited me had a comprehensive list of reasons for the ringer signal causing modems to loosing sync on a long line. He never noticed my home plugs or turned them off!

  • First he checked the phone line for noise,  N9none)  possible faults/ poor joints: (fixed)  however  excessive capacitance was noted
    Then he checked the routing of the cables in the home . no problem there
    he Checked the NTE and faceplate for the latest version
    Checking with his test equipment there were a massive amount of FEC errors, these really clocked up massively on the ringer pulse .
    he asked for settings in the exchange to be modified
    he changed the DSLAM in the exchange.




The problem was still there.
he phoned BT OR technical help and they told him about the incompatibility issue on long lines between System X exchange equipment and Ferranti Mk 2 DSLAM in BT exchanges. BT OR then did something remotely and Hey Rresto! I now have a brilliant stable connection that has not lost sync due to a phone call for 6 weeks. What is interesting is that router stats shows the following data which is significantly different to what it used to be .. I will explain.
Downstream
Noise Margin:  6.7    dB
Bandwidth:    1696  kbps
Attenuation:  63.5  dB
Power:        16.6  dBm
noise margin used to show as around 12 dB
Bandwidth used to vary between 1000kbps and 2000 kbps
Now both are stable and never vary
Over a ten day period we now have
Errors:
  FEC:  145369
  CRC:  7309
  HEC:  20983
where as that used to be typical over a few hours!!

Failures since last reset:
  LOF:  0
  LOS:  0
  LPR:  0
  ES :  3622
Community Veteran
Posts: 19,100
Thanks: 437
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Registered: 31-08-2007

Re: Long Line and possible interference issue

No doubt that was YOUR problem gpsmount, but that is NOT the only reason for loss of sync when the phone rings.
runhare
Aspiring Pro
Posts: 512
Thanks: 47
Fixes: 1
Registered: 09-10-2007

Re: Long Line and possible interference issue

my point exactly, but it took 5 years to get an engineer who  eliminated all possible causes until a solution was found.!
Community Veteran
Posts: 19,100
Thanks: 437
Fixes: 21
Registered: 31-08-2007

Re: Long Line and possible interference issue

These type of problems are a real pain in the **** because there are those that are intermittent issues and are difficult to track and then cases yours where the majority of the "engineers" don't have the knowledge to get to the bottom of more complex issues.