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Topic # 108819 6-Sep-2012 09:46 Send private message

I have recently been troubleshooting an ADSL problem for a friend. He has a standard ADSL2+ connection split at the wall by a Vodafone supplied filter.

Recently, he noticed his connection dropping and the phone began crackling while in a call. The crackling is only heard by him, not the calling/called party (which I thought was weird)

Initially I figured it was a faulty filter, given that the problem was new, so we replaced it but the problem persisted.

Next I checked for faulty equipment in his house. He only has one jack point so there were no sneaky phones plugged in directly. He doesn't have Sky or a monitored alarm either :\

I removed the filter and modem and plugged the phone directly into the jack and called 120. The call was crystal. The modem! I hooked him up with a Vigor 120 a couple of years ago and it has been rock solid since then but I figured maybe two years was its lifespan...

I checked the modem admin portal and sure enough, saw a hew hundred recorded RX CRC errors. I watched it for a time and they would build up (sometimes into the thousands) then the modem would lose connectivity and reboot to begin the cycle again.

I went home and grabbed my Vigor 120 (known to be good, never dropped connection and I work it hard) and dropped it in (I used my AC adapter and cables) and saw identical behaviour.

I don't have another spare modem on hand to test (I'm waiting for my brother to bring his down) but does anyone know what might be causing this?

I have also tested running just the modem -> filter -> jack and still see RX CRC errors popping up as soon as the modem reboots.

Modem stats are as follows:

Mode: ADSL2+(G.992.5)
State: SHOWTIME
Up Speed: 977022
Down Speed: 14642423
SNR Margin: 11
Loop Att.: 18

The stats are pretty good for ADSL2+, I have seen the SNR Margin & Loop Att. fluctuate some but can't reliably reproduce the fluctuations.

TIA for any insight.

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  Reply # 682547 6-Sep-2012 20:38 Send private message

As soon as I hear the word crackly I think an imbalance in the line. This can be as simple as the plug in filter going faulty or it could be something more sinister like the feeder pairs in the street going faulty. When you unplug the modem do you also remove the filter and test the line? Or you have a clear call via the filter? That would be the first to check. Next thing is the line cords themselves. However, you say the call is clear when the modem is removed so guessing the line cords will be fine. My guess is the plug in filter though.

172 posts

Master Geek


  Reply # 684152 10-Sep-2012 22:18 Send private message

To check if the filter was dodgy, I would suggest plugging the modem direct to the jackpoint. Just use a known good phone cable.

If you are still getting errors, ask your ISP to run a Line Quality test to see if it is bitswapping or some other physical issue on the line.



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  Reply # 685727 13-Sep-2012 17:36 Send private message

Thanks for the suggestions guys. As it turns out, the line from the road to the demarc was very dodgy. I called the Chorus tech who took a look and noted that there were exposed wires hanging down the exterior wall.

We checked the filter, phone and modem before calling the techs so we were confident it wasn't one of them afterward.

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