Varying dsl snr margin

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nickb800

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#64041 6-Jul-2010 20:25

A quickish question:
On Telecom DSL our Linksys WAG200G modem (latest firmware) was loosing sync last week so upon investigation I noticed that the downstream SNR margin has been sitting quite low at around 6db, but also varying from 4 to 12db over short time periods.

Of most interest to me was the variation in margin, the 4db seemed a little ridiculous to me from what I had read suggesting that the modem might be telling porkies (I understand that linksys arent great on alcatel dslams)

Is this indicative of a fault on the line even if we are no longer experiencing loss of sync?

We have a master dsl splitter installed, and I have read the brilliant post on connection statistics here
http://www.geekzone.co.nz/forums.asp?ForumId=49&TopicId=10835
We have had issues with water ingress at the street connection in the past.

Cheers

raytaylor

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#348567 6-Jul-2010 21:45

Three things
- Do you have line noise or wooshing / clicking sounds when you call 0800-000-000 with a standard corded phone?
- Check your signals with another modem
- Call your isp and ask for a port reset on the dslam (can take up to 24 hours)

If the issues have stopped, it may have been weather problems with water in the line or wind moving the cables on the telephone pole. Also could have been interference near your line.
I have a client who lives on a back section. When the people in the front house come home, their internet usage affects the stability of the connection in the back house because of the interference between pairs in the trunk cable back to the cabinet.

Ray Taylor

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nickb800

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#348845 7-Jul-2010 20:24

Great thanks for that ray. Only a very faint hissing noise on the landline, and I dont have another modem.
Called telecom and they monitored the line for 24hours which showed 20mins of lost sync in total so will send out a tech tomorrow. They seem to think the issue is in the house but given I have a master filter I doubt it (unless the filter itself is faulty).

webwat

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#350268 12-Jul-2010 14:30

raytaylor: Three things
- Do you have line noise or wooshing / clicking sounds when you call 0800-000-000 with a standard corded phone?
- Check your signals with another modem
- Call your isp and ask for a port reset on the dslam (can take up to 24 hours)

If the issues have stopped, it may have been weather problems with water in the line or wind moving the cables on the telephone pole. Also could have been interference near your line.
I have a client who lives on a back section. When the people in the front house come home, their internet usage affects the stability of the connection in the back house because of the interference between pairs in the trunk cable back to the cabinet.

Port reset wont make any difference because its able to resync whenever it drops. Fluctuating noise margin generally means a bad connection somewhere on the line, faulty splitter, or crosstalk with other ADSL lines. In some areas there are just too many ADSL users given the quality/distance of the telecom lines in the area, so changing to a different cable pair can help, which the tech may do if no other problems show up. The link from splitter to ADSL outlet should preferably be Cat5 to prevent interferance on the house wiring.

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adslgeek

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#350383 12-Jul-2010 19:33

Hey just a clarification:

Regarding Ray's comments/Telecom certainly seems like there is some sort of physical layer issue (eg line issue) I agree it is less likely to be internal wiring due to full install, but not impossible.

One note though - I see a heap of people getting SNR (Signal to Noise Ratio) mixed up with SNMR (signal to Noise Margin Ratio)

The simple description is that they are different -
http://www.kitz.co.uk/adsl/linestats.htm#SNR

http://www.kitz.co.uk/adsl/linestats.htm#SNR_Margin

This excerpt is from Kitz website of course - if you
"Whilst SNR Margin and SNR are related, they are not the same thing.
SNR Margin could be thought of as a "buffer zone" which is there to protect your connection against normal SNR fluctuations that can and do occur on a daily basis."

nickb800

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#350392 12-Jul-2010 19:59

adslgeek:
One note though - I see a heap of people getting SNR (Signal to Noise Ratio) mixed up with SNMR (signal to Noise Margin Ratio)

Ahh thats very helpful thanks. The router is at my parents house and I am back to varsity now, but from memory it was an 'SNR margin' that was varying wildly. Makes a lot more sense as it often fell to ~6db which according to whistleblower's post here http://www.geekzone.co.nz/forums.asp?ForumId=49&TopicId=10835 would barely support sync if it were a SNR figure.

Telecom guys came along and isolated the line to run a few tests. They forgot the power supply for their modem so couldnt test if it was a modem issue. They couldnt find anything.

Was not impressed by the condescending tone towards me; I got the impression they were working from a standard problem resolution script. They gave me a little lecture that it was a good speed for adsl1 despite me saying that speed wasnt the issue, it was the disconnections. Also they gave me a spiel that the internet over wifi can be affected by microwaves etc, even though I had told them explicitly that it was the modem loosing sync (proven by the lost sync over the 24hour monitoring period).

So will have to have another look in a few months when Im back. In the meantime I'll enjoy a stable adsl2+ connection at my flat :)

@webwat
Most neighbouring streets are not wealthy, and we also have a few neighbours on telstraclear cable, so I suspect the number of dsl users should be quite low thus making crosstalk less of an issue. But I will mention switching pairs if I have the pleasure of meeting the chorus/downer techs again.

Appreciate the assistance!