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joefolkes asked on

Broadband SNR very low all of a sudden

Hello EE,

I have a SBS network, with an ADSL router connected for Broadband access.

One morning I notice internet was sluggish, timing out here and there, and generally a pain to navigate. After checking the ADSL router I saw the below picture (those errors are over a few hours period, over night)

The downstream SNR so very low, and flickers between 4 and 10, I have never had a problem previously on this line, and I havent changed any hardware at all

The broadband provider is AOL UK.
The line/exchange is owned and run by BT.

Tried changing usually settings MTU, PPPoA etc. Also tried changing filter. All did nothing.

My question is what has caused this, and is it AOL UKs problem? BTs problem?

Any suggestions on what I do next?

Many thanks


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Last Comment

8/22/2022 - Mon

Hmmm, attentuation looks a bit on the high-side and your snr numbers are definitely a problem.  Perhaps there is an issue with a adjacent pair (wire) making a poor contact with your wiring.  I would recommend calling you ISP and have them run a line check and see if there is a possible issue with their (ISP) wiring or the DSLAM port.


Do you have a filter on the outlet the 3com's plugged into, like

http://www.shop.bt.com/productview.aspx?Quicklinx=4D46 ?

Or do you have it plugged straight into an 'ADSL master socket'? (those have a filter built in.)

Ideally, you would still have one of those filters on all the other outlets that have devices plugged into them.

Also, microwave ovens, 2.4GHz cordless phones, some baby monitors and other wireless 11b/g routers or APs nearby (if they're +/- 4 channels within the channel you're using) can cause higher noise levels too.

Its on a BT master socket, and there are no extensions on it.

Yes it is on a micro filter , which i have tried changing with several others, to no effect.

Checked for interference, unplugging everything, again to no effect.

Anything else i can try?

Many thanks
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James Murphy

If you live in an urban area, the noise isn't necessarily coming from your own home, of course.

You might look around with the Site Monitor on your wireless card's utility, but if all you have is the windows zero configuration service try a program like netstumbler (http://www.stumbler.net or http://www.netstumbler.com).
The wzc service's 'View Available Wireless Networks' screen doesn't separate mulitple radios on different channels using the same SSID.

If a neighbor recently got a draft-N router and is using a 40MHz-wide channel in the 2.4GHz band the only noise-free channel you'll have in the G band is 11 (+ 12 & 13 if those channels are available in your location, but those overlap and interfere with 11, as well). I don't know for sure if that would even show up on a wireless G card if they have the router set to 'N-only' rather than mixed mode.

Have you done any throughput tests to see how accurate the up/down rates shown in the 3com screens are?
e.g. http://www.speedguide.net/speedtest/
For a good baseline run the test multiple times from 3 or 4 different sites there, at different distances from you... say, one from the europe mainland, one in the UK, one from NZ, and one in the US. If you copy & paste the results to a text file you can refer to them and run the tests again to the same sites in the future to verify if you're actually running faster or slower (perception of how fast web pages load doesn't always reflect actual throughput).

If you're _lucky_ the noise is in your phone line, because then you have a better chance of getting rid of it without it costing you quite a bit of money.


Live out in a small village, so no other wirless connections around.

Had a few restarts of the router, to which it has sync'd at a lower speed of 4555 kbps, this has increased the SNR to around the 13 mark. Still instable and time outs, but better.

So is there a way to force router to sync lower, to increase SNR?

Did a couple of speed tests, which seems ok (if they don't time out to start with). Tried doing a big download, to which i get the full 450kbps, seems once i get it started its fine.

Any more suggestions?

« SpeedGuide.net Speed Test Results »
2943 kbps down (~2.94 Mbps, 359 KB/s)“ 
329 kbps up (~0.33 Mbps, 40 KB/s)‘ 
500 KB downloaded in 1.392 seconds 
1024 KB uploaded in 25.505 seconds 
Tested on: 2008.05.23 10:52 EDT 
Tested from: hosting-needs.com 
Test Link: http://www.speedguide.net/speedtest/results.php?test=YOKVN9F4QKQ8 
Latency: 175ms
« SpeedGuide.net Speed Test Results »
1990 kbps down (~1.99 Mbps, 243 KB/s)“ 
240 kbps up (~0.24 Mbps, 29 KB/s)‘ 
250 KB downloaded in 1.029 seconds 
500 KB uploaded in 17.07 seconds 
Tested on: 2008.05.23 10:56 EDT 
Tested from: celticsurf.net 
Test Link: http://www.speedguide.net/speedtest/results.php?test=EK256A7HUA1H 
Latency: 173ms
« SpeedGuide.net Speed Test Results »
3070 kbps down (~3.07 Mbps, 375 KB/s)“ 
369 kbps up (~0.37 Mbps, 45 KB/s)‘ 
500 KB downloaded in 1.334 seconds 
1024 KB uploaded in 22.731 seconds 
Tested on: 2008.05.23 10:59 EDT 
Tested from: feier-tiere.de 
Test Link: http://www.speedguide.net/speedtest/results.php?test=QMJFCRNMW2QY 
Latency: 176ms

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There's definitely something not kosher when your router sees 4544bps down and your system is only getting between 2.94kb and 1.99kb down.  How many PCs are on your LAN are accessing your Internet connection?  LAN users internet access restricted (intranet access only) or is the network fairly open (e.g., possible P2Ps, streaming audio/radio listeners, IP TV watchers, large downloads, etc)?  Any major LAN apps users may be accessing??  

BYW, what is your MTU set at?  Lets say your default value is 1492..  At the cmd prompt enter "ping -t -f -l 1470 yahoo.com" & if you get "Packet needs to be fragmented but DF set" error - keep reducing the packet size by 10 (e.g., 1460, 1450, 1440, etc), until you get a packet reply "Reply from bytes=1460 time=56ms TTL=47".  Then start increasing the packet size by 1 (e.g., 1451, 1452, 1453, etc) until you get another (DF) failure...

In my example above, when you add 28 (ping/ICMP packet) to the final pass value of 1460, my max MTU would be set to 1488.  In my case, were the default of 1492 would likely work, but it is subject to random fragmentation.  Also, if you are running any VPN(s) (high encryption overhead), having probs transferring any moderate amounts of data will likely be subject to repeated attempts.

A little more food for thought for you Joe...

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Rereading your posting...  the items I mentioned will NOT change poor SNR, which is primarily attributes related to the ISP physical network.  In some cases, poor/bad inside wiring and DSL filters will influence SNR.



Thanks for the reply.

MTU set at 1400, which is an AOL restriction and their recommended.

I do get full speed on other downloads (once they get started), just speed test a little off'ish.

So if poor SNR on master socket, this would mean either ISP or BTs fault?


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