Intermittent Fault causes ATM CRC errors

Hello all,

This is my first post here at thinkbroadband so please be gentle with me

OK so this is a bit of a stumper and because it's intermittent ZEN are reluctant to pass it on to BT just yet!

I'm using a Draytek Vigor 2820Vn on an ADSL 2+ line (G.992.5)
Sync Speed 19.7 Mb DOWN 12.3Mb UP
SNR Margin 3
Loop attenuation 22

Speed Test gives 17MB down and 0.9 Mb Up

From time to time I get no, or very slow throughput trying to load web pages. During this event the router is ramping up hundreds of ATM cell CRC errors every few seconds, even if I am doing nothing on the Internet. A BT quiet line test shows the line has no noise.

During the event the SNR Margin drops to 1
After the event the SNR Margin is back at 3 and no CRC errors and a speed test gives 17Mb up and 0.9 Down again.

The router does not need to be rebooted, but doing so makes no difference.

The effect is almost like a denial of service attack flooding the router with ATM CRC errors.

I'm guessing that it is some kind of noise or crosstalk but have no idea how to get this escalated. Since the problem is intermittent the chances of an Openreach engineer being on site during an event is slim.

Has anyone heard of, or experienced this kind of problem. Any advice or diagnostic help would be appreciated.

Thanks

John.

A new microwave cooker perhaps?

RobertoS

Wish it was that simple

I believe OpenReach have specialists for cases of intermittent noise (which is probably what this is). Trouble is that these days you could well be charged a lot of money if they don't find anything which is why Zen are reluctant to advise this. Unless you can track down the noise (new business using industrial equipment perhaps) then you may find it very difficult to progress this any further.

Ultimate solution would be full fibre - but unless you are lucky enough to live in an FTTPoD area with a good chunk of spare change then this is not going to help.

Thanks ian72

Can't even get FTTC They Fibred the whole estate EXEPT our cabinet (Which is only 100 yards away from another cabinet which has been fibred)

I hate problems like this because they are so difficult to resolve.

I've worked in IT for years and have often had to try and work on intermittent issues - they are as painful for the fixer as for the fixee. People always assumed I thought they were lying if they couldn't reproduce the problem - trouble is without seeing it you often can't get the info you need to get anywhere near fixing it.

I know how you feel and wish I could offer some nugget that would give light at the end of the tunnel, but I'm afraid I can't do anything so helpful as that.

Almost certainly an "external event" generating noise. IT may not be in your house, but could be next door or anywhere along the line.

Is there a pattern to the bursts? Are they regular, every XXX minutes? Or do they tend to occur at specific times? How long are they? A few seconds or a couple of minutes?

Get RouterStatsLite and get it running over several days monitoring Sync and SNR to see if there are patterns to the problem and if it is literally switch on and off, or ramps up slowly.

Hello MHC

and thanks for your help

There is no strict pattern to the events, however since this started, every Saturday and Sunday morning between 10:00am and 1:00pm I will experience an event which lasts around 1 to 1.5 hours after this the line stabilises with a couple of CRC errors every few minutes. maybe later on in the day there will be shorter bursts of errors. Late on Sunday evening all the CRC errors stop, and the line is rock solid.

During the week I might randomly get shorter bursts (today for instance nothing at all until 4:30pm'ish then around 5000 CRC errors in 20 minutes, then the line has stabilised again.

It's really weird and very frustrating.

I'll download RouterStats - Lite and see if I can gather more information, Thanks for suggesting this.

John

RSL will run continually - set it for 15 second samples and to auto save the graphs. At least then you have some records. Locating the problem is another issue entirely!

Roberto's suggestion about a microwave, may sound silly but it could well be one of those close to the line, or an arc welding set, or ...

Then the age-old questions re Sky boxes, DECT phones, their respective power supplies, newly failed filters, and so on. I just went for the first thing I thought of that might have been recently replaced.

Edited by RobertoS (Mon 04-Aug-14 18:55:56)