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Author Topic: ADSL Noise Margin Variations - worth investigating?  (Read 3371 times)

aesmith

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ADSL Noise Margin Variations - worth investigating?
« on: November 13, 2015, 01:02:58 PM »

Hi,

Our line (20CN ADSL 1 Max) shows regular but small scale variations in downstream SNR, showing as variations in the Noise Margin as reported by the router.   Variation during the day is round 0.3dB, with what appears to be a regular pattern.   Towards evening the noise margin reduces and the variations become larger and more random.

See attached graphs from Routerstats Lite, one showing typical daytime pattern, one the night and one showing the transition.   

Questions - given that the router is staying synched throughout, what's the likelihood that these variations are actually causing any issues?  And secondly, does that repeated pattern match any sort of known interference source?   It seems to be around a 4 minute cycle.

Router is a Linksys WAG320N by the way.

Thanks, Tony S
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JGO

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Re: ADSL Noise Margin Variations - worth investigating?
« Reply #1 on: November 13, 2015, 01:15:30 PM »

A possible explanation is radio broadcast interference from a distance which increases at night due to improved propagation, from "negligible" to  "marginal"  .
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burakkucat

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Re: ADSL Noise Margin Variations - worth investigating?
« Reply #2 on: November 13, 2015, 05:00:26 PM »

. . . given that the router is staying synched throughout, what's the likelihood that these variations are actually causing any issues?

Would you be aware of those variations if you were not monitoring the circuit's statistics? If your answer to my question is no, then you have, essentially, answered your own query, quoted above.  :)

That said, I agree it would be interesting to know the cause of those regular variations.
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aesmith

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Re: ADSL Noise Margin Variations - worth investigating?
« Reply #3 on: November 13, 2015, 07:28:56 PM »

Hi, no I probably wouldn't.  The only caveat is that my router doesn't have any error stats.   I don't know is whether these variations are causing errors.
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burakkucat

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Re: ADSL Noise Margin Variations - worth investigating?
« Reply #4 on: November 13, 2015, 10:54:46 PM »

Hmm . . . Not knowing anything about a Linksys WAG320N modem/router, I had to search for information and see that it is possible to configure the LAN1 port as a WAN port.

So . . . if you are not using all four LAN ports, you could configure LAN1 as a WAN port. Then with a HG612 (from eBay), flashed with Wolfy's unlocked firmware image and configured as a pure bridge, you could use that (temporarily) between the line and the WAG320N. (LAN1 port of the HG612 to the WAN port of the WAG320N.) The LAN2 port of the HG612 would then allow you harvest circuit statistics with the use of one of the two recommended utilities. (Either DSLstats or HG612 Modem Stats.)

Personally, to be honest, I would not bother.
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aesmith

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Re: ADSL Noise Margin Variations - worth investigating?
« Reply #5 on: November 14, 2015, 08:53:54 AM »

Thanks. Interesting idea, I might look into that if I can pick up an HG612 cheap or preferably free.  I haven't read all the info, but can DSL stats still talk to the HG612 when it's in bridge mode with the router doing PPPoE? 

Although I don't particularly like the idea of an additional box, another option would be to get a Cisco 877 which seem to be readily available on Ebay.  The Linkys would then purely act as AP and switch with the 877 doing DSL, NAT, firewall, DHCP.  Then all stats would be available via SNMP.

Of course it goes against the grain to have to buy anything purely to try and force the ISP to work on a fault.
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roseway

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Re: ADSL Noise Margin Variations - worth investigating?
« Reply #6 on: November 14, 2015, 10:37:40 AM »

Quote
I haven't read all the info, but can DSL stats still talk to the HG612 when it's in bridge mode with the router doing PPPoE? 

Yes, and you can use HG612_Modem_Stats as well. The details are here: http://www.kitz.co.uk/routers/hg612unlock.htm#hg612_linestats
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aesmith

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Re: ADSL Noise Margin Variations - worth investigating?
« Reply #7 on: November 14, 2015, 04:39:31 PM »

Yes, and you can use HG612_Modem_Stats as well. The details are here: http://www.kitz.co.uk/routers/hg612unlock.htm#hg612_linestats
Perfect, sorry for not looking for myself.  I might possibly be able to get an HG612 free, from a site where we've taken the line direct into a VDSL card in the router.
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