ADSL CRC errors / line noise

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MrTomato

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#55362 31-Dec-2009 18:06

A very happy New Year, everyone! I was wondering whether anyone could give me a bit of advice...

I'm having some intermittent line noise problems which have come back since the cabinet I'm connected to was upgraded to ADSL2+ a couple of weeks ago. Aside from intermittent audible noise while making phone calls, my ADSL router has been reporting relatively high levels of RX CRC errors (>1000 per 24 hours, and no TX CRC errors). The ADSL connection hasn't been dropping, however.

I'm on Telecom's Pro plan with interleaving switched off, and if possible I'd like keep it that way as I'm a fairly heavy VoIP user. I've isolated the internal wiring by connecting a BT socket directly to the demarcation point (sorry if I'm not supposed to do that!) and the CRC errors were still appearing at the same rate, so the issue is definitely somewhere at Telecom's end. The router reported loop attenuation of 8dB when it was connected to the demarcation point.

I'd really like to get this sorted out, but I'm not sure what the best way to proceed would be. I'm presuming it's a physical cabling problem somewhere down the line. Since the problem isn't causing my connection to drop, would Telecom even count it as a fault? If they would, what would be the best way to report the problem, and what would be the best thing to say to trigger some action? I had a similar problem a couple of years ago, and 120 were a bit of a nightmare.

Thanks everyone!
Mr Tomato

cyril7

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#286315 31-Dec-2009 22:50

Hi Tom, tell us a bit about your house phone wiring

Cyril

richms

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#286321 31-Dec-2009 23:12

He just did! a master socket at the demarcationpoint and the errors persisted.

how much over 1000 is the big question. a few 1000 over a day of heavyuseisnothing .

Richard rich.ms

MrTomato

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#286341 1-Jan-2010 08:57

Thanks for your replies!

The router's been up for a few days, but according to the uptime and number of CRC errors, it's an average of 7147 CRC errors per day.

According to a few Internet searches, I believe that anything over a few hundred CRC errors a day, and certainly a thousand a day, would indicate a line problem; but I suppose the question is whether Telecom feel the same way. I used to get pretty much zero from one day to the next with vanilla ADSL. (By the way, I forgot to say in my original post that I tried another ADSL router with the same result!)

Regarding the house wiring, I tested directly at the demarcation point and continued to get CRC errors, but internally it's star-wired. It introduces 2dB of attentuation but is solid and doesn't seem to be noisy. I'd like to install a home distributor cabinet per PTC 106 sometime in 2010 so that I can fit jackpoints around the house for the home LAN and manage phone and LAN at the same point.

cyril7

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#286343 1-Jan-2010 09:07

Hi, sorry should have read your post correctly first time. You say you tested at the demarc but I presume you did not disconnect the rest of the house when doing that test as that is important. While there are lots of errors, I dont think the number you are getting is way out there, then again I have no errrors with a 5week uptime.

Regardless, there are lots of reasons for errors, the most simple being bad joints, but typically these would also be noted in the voice band, either crackling or hum, and you have not commented on that.

The more likely issue is simply the modem/Dslam using line spectra thats not suited to reliable transport. The normal way to fix this is for Telecom to apply a more conservative profile, this will have the effect of a slight reduction in sync rate but may proclude some bins (carriers) that are marginal in S/N that currently are contributing to high errors. What is the report noise margin, purhaps you could post the full ADSL stats from you modem (which is a what model?).

Another simple test you could do for now is reduce the spectrum usage to 1.1MHz, ie force either ADSL1(G.DMT) or ADSL2 rather than ADSL2+.

Cheers
Cyril

MrTomato

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#286356 1-Jan-2010 10:58

Hi Cyril -

Thanks for your reply!

I did disconnect the house wiring when I tested at the demarcation point - there was plenty of surplus incoming cable so I connected a jackpoint directly to the incoming wires. Sorry if this is a no-no, but I wanted to be sure. The internal wiring is now reconnected with fresh Scotchlok connectors.

I do have intermittent audible crackling on the line while I make phone calls. Sometimes it can be very bad, and other times there's no audible crackling at all. I had essentially the same problem a couple of years ago, intermittent in the same way, and it was a nightmare trying to get 120 to do anything! Fortunately it eventually started crackling while I was speaking to them. The problem was resolved back then by connecting my line to the cabinet rather than the exchange, and roughly since the cabinet has been upgraded to ADSL2+ the problem has come back. If this problem is the same as the one I had before, I suspect the line gets worse when there's a big change in humidity.

The ADSL router I use is a Draytek Vigor 2700, which has been rock solid to date. I've also tested the line with a Dynalink router with the same issues. The Vigor comes with a downloadable range of different modem firmwares - I've tested all of them, and it's currently on the most conservative one. There are certainly progressively fewer CRC errors when it connects at slower speeds.

These are the stats from the horse's mouth:

--------------------------- ATU-R Info (hw: annex A, f/w: annex A) -----------
   Running Mode            : ADSL2+(G.992.5)       State                : SHOWTIME
   DS Actual Rate          : 18204000 bps   US Actual Rate       :   732000 bps
   DS Attainable Rate      : 18204000 bps   US Attainable Rate   :      168 bps
   DS Path Mode            : Interleave    US Path Mode         : Interleave
   NE Current Attenuation :       11 dB    Cur SNR Margin       :       12 dB
   DS actual PSD           :    19. 8 dB    US actual PSD        :    12. 5   dB
   ADSL Firmware Version   : 121201_A
-------------------------------- ATU-C Info ---------------------------------
   Far Current Attenuation :        4 dB    Far SNR Margin       :       12 dB
   CO ITU Version[0]       : 0000494b       CO ITU Version[1]    : 00004e53
   DSLAM CHIPSET VENDOR    : < unknown >

(It says interleaving is on, but actually it isn't.)

Cheers!

richms

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#286401 1-Jan-2010 15:34

Get the crackling fixed. If it is audible it is a fault, and if you are paying the wiring maintanance they will usually swap out all your sockets to 2 wire ones if you have old master/secondary ones.

If the crackle is still audible with a socket at the demarc then it doesnt matter about the wiring maintanance, as its outside anyway.

Again, someone is let down by the pathetic idea of a demarc that telecom use in having to hack wiring around to test it.

Richard rich.ms

cyril7

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#286408 1-Jan-2010 15:55

Hi, yes you must get the poor connection/joint on your line sorted before anything else can be determined.

I have dealt with numerous situations recently where people have been moved to cabinets and things have gone downhill due to poor connections, in all these cases its simply a bad termination on the cabinet MDF when their line was moved over, a 20sec repunch of the line jumpers by a chorus tech and its all good, hardest part is getting past the CSR to get the line checked.

Cyril

MrTomato

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#286412 1-Jan-2010 16:11

Thanks Richard and Cyril - I really appreciate your replies. I'll call 120 and chase up the crackling on Tuesday, then, and take it from there.

Out of interest, will the phone cable coming to my house be one long cable from the roadside cabinet, or will there be other connections along the way? There's a grey cylinder with 'TL ' marked on it a few metres away from the house, and a small ankle-height green cabinet next to it. What do they do (assuming they're part of the telephone network)?

Thanks again!

cyril7

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#286417 1-Jan-2010 16:37

Hi the grey plastic post type pedestals that are around 75-80mm in diameter are Telecom, the green plastic square boxs are most likely power.

The street distribution cables are typically a continuous run from the cabinet (originally a cross connect cabinet and now an active DSL wisper one) however joints out in the street can do happen, all depends on how the cable was layed at the time, but joints are kept to a minimum.

From the exchange to the cross connect cabinet are typically 100 or 200 pair feeder cables, then from the cross connect cabinet 25 or 50 pair distribution cables are layed as suburbs roll out. At each pedestal normally 4 pairs are dropped off, ie two for you and two for your neighbour. In the cross connect cabinet the feeder lines from the exchange are jumpered to a distribution pair and on to your house.

When cabinetisation occurs several things can happen, but typically the voice services continues to be fed from the exchange via the feeder cable to the MDF in the cabinet. This voice service from the exchange is coupled with the local cabinet DSL service with a splitter/filter, the output of the splitter/filter is jumpered to your distribution line etc

What I am trying to say here is that the crackle on the voice part of your line could be coming from a section of cable that is not traversed by your DSL service. However in all probability it is so you need to have it sorted before making any further DSL related checks.

Cyril

MrTomato

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#287552 6-Jan-2010 19:29

Just checking back in to update the thread...

The Chorus man came out today, and he was excellent - very conscientious and pleasant.

He spent quite a long time systematically testing and redoing all the connections between the house and cabinet, and changed to a different line (which I presume means switching to a different pair on the same cable), but unfortunately I suspect it hasn't made any difference.

Sod's law: There was no audible crackling on the line today while he was here - it's been having a good few days, probably because there's been no rain or big change in humidity recently - but the ADSL router is still reporting CRC errors fairly thick and fast, albeit at a slightly slower rate than before for some reason.

The upshot is that he suspects the cable itself might be damaged somewhere, so the plan at the moment is to wait until the crackling reappears and then I'll call 120 again while the fault is still present and audible. Assuming the crackling and CRC errors are related, perhaps if / when it's finally sorted it'll resolve both issues!