Noise Margin & dropped connections

Noise Margin & dropped connections

Postby flyinggizmo » Mon May 13, 2013 5:02 pm

NoiseMargin-2013May13-1658.jpg
Monitoring noise margin & connection speed with Routerstats. I was watching BBC IPlayer when connection dropped for about 20 seconds. On checking routerstats the noise margin was appx. 2.2 db, then suddenly dropped to zero and then maintained 3.9 db after the dropped connection for about 20 minutes before dropping again. I've never seen this before. Could it have something to do with Impulse Noise Protection that I've turned on? Any advice appreciated. thanks.
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Re: Noise Margin & dropped connections

Postby flyinggizmo » Mon May 13, 2013 5:09 pm

NoiseMargin-2013May13-1707.jpg
Another screenshot!
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Re: Noise Margin & dropped connections

Postby Philip_L » Mon May 13, 2013 6:05 pm

Hi

It is unlikely to be impulse noise protection as I don't think any ISP actually uses it, just turning it on at your end is just saying, "Lets us it if it is available" so for most people it does nothing at all.

Unfortunately ADSL is affected by noise and it could come from anywhere. It sometimes just takes one other person to get ADSL and they happen to be bundled up against your pair of telephone wires for you to lose quite a bit of sync speed due to cross talk.

The SNR is a margin, it is the amount above and beyond what is required at the moment you sync with the exchange. If you have too little, then noise is more likely to erode that margin and cause your modem to drop.

ADSL was never designed to maintain a guaranteed connection, it is expected to drop perhaps a few times a day unless you are very lucky or run with a very high margin of SNR. This is the result of pushing old telephone cables to the limit.

I wouldn't worry about it unless the drops are so frequent they are really a pain in terms of you can't do very much at all.

Also what are you other line stats such as attenuation and sync speed?

Regards

Phil
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Re: Noise Margin & dropped connections

Postby flyinggizmo » Mon May 13, 2013 7:12 pm

Attenuation up/down: 23.8 / 45.0 Connection speed is 6147 kbps.

I have to be honest I'm using the 7800n to reduced the SNR down from 15dB to about 3 dB using the SNR "tweak".

Without the tweak my connection speed is about 3100 kbps.

I just can't understand the wild fluctuation in the graph as normally everything is very stable for weeks at a time.

I've recently upgraded the firmware. I'll turn off the impulse noise protection anyway if it's not doing anything useful.

Thanks for your help Phil.
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Re: Noise Margin & dropped connections

Postby Tomken » Mon May 13, 2013 9:44 pm

I found that when I had PhyR enabled, it seemed to keep the SNRM low when it did drop.

A channel change may help if you are getting interference from other users.

Download inSSIDer http://www.metageek.net/products/inssider/ - click on Networks and it will show any other users around you and on which channel they are using.

Optimum channels are 1, 6 and 11 as they can't be overlapped as they can by a stronger signal strength user on an adjacent channel.

You should ideally be looking for a channel that will give you a signal strength (RSSI) of around 50 or less with no other near users of the approx. same strength on that channel or adjacent.

If there are any other users on any of the optimum channels that will give you that RSSI value and any other users on the same channel or adjacent where their RSSI >=76 then you can safely use those.

If having found the best channel for you and you still experience these SNRM drops with PhyR disabled, then you should contact your ISP as there could be a line fault - but try changing the microfilter first if you use them.
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Re: Noise Margin & dropped connections

Postby flyinggizmo » Tue May 14, 2013 7:20 am

Thanks Tomken. However the computer is a wired connection. I've run inSSider program on my wireless machine and there doesn't
seem to be any wireless conflicts with neighbours etc. It's using channels 1 + 5. Thanks for your help.
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Re: Noise Margin & dropped connections

Postby Tomken » Tue May 14, 2013 10:11 am

Your tweak down to 3dB may be too low for when the line gets noisy - usually in the evenings or at peak times.

At one time my SNRM (tweaked to 4.5 at the time) would drop to 0.4dB late at night and for the most part would hang on with just the odd DCs, but would lag quite heavily when on wireless - so I'd wire up about that time which would increase it.

Try setting it to 4.5dB as stability shouldn't be sacrificed for speed, but contacting your ISP for a line test wouldn't go amiss.

My Downstream Attenuation is 49 and I'm currently getting a sync speed of 6826 on 6dB with TalkTalk's LLU, but it does depend on the quality of the wire and number of joints in the line - although I would have expected a better speed than 6147 on 3dB and Atten. of 45.

15dB is quite a high line profile for that Attenuation and is usually set at that by whatever auto line management your ISP is using to stabilise the connection - have you recently incurred a large rapid number of resets because of tweaking the SNRM or is it because your connection has previously been unstable ?

Line management programs usually see these as an unstable connection and increase the SNRM accordingly but you could ask your ISP to reduce your profile - having reset the router to default first.

Also ask your ISP if they use SRA as their Line Management system and if so, then enable that in the router.
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Re: Noise Margin & dropped connections

Postby flyinggizmo » Tue May 14, 2013 10:46 am

Thanks Tomken. I've had the modem connect for months without a disconnect although there have been "spikes" generally around the same time every night when the signal has dropped to zero but the modem didn't disconnect. Usually these spikes only last 20 seconds or so before the speed returns to normal. Then there are periods when there are no spikes for weeks on end. Before purchasing this modem the Orange Livebox would constantly disconnect especially in the evening which probably explains the high 15dB line profile. However, I've had the 7800n now for nearly a year so I would have thought the profile would have increased by now. I'm beginning to think the same as you, that it's a line fault. The big problem with that is it's a BT line operated by Orange and in the past Orange have done a line check with me on the phone which doesn't prove anything! Would it be a good idea to return the 7800 to default settings and complain again to Orange about the high line profile? I've eliminated all the house wiring by getting an engineer to install a socket directly into the house from the pole outside so there are no extensions, internal wiring etc. that could cause interference. In the past I've found Orange are good until something goes wrong and then they're hopeless. Trying to upgrade a problem to a Dept. that can do something about it is a nightmare! That's why I bought the 7800 in the first place because I couldn't get them to reset my profile, so I thought I'd do it myself!
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Re: Noise Margin & dropped connections

Postby Tomken » Tue May 14, 2013 2:13 pm

If you report it as an intermittent fault, then that should warrant further investigation by Orange if you still get the dropouts with the SNRM set to default when wired and if they refuse to lower your profile after all this time with a now mainly stable connection - then use the old favourite of threatening to look for another ISP to get the speeds that you should be getting on that Attenuation.

Did the engineer just fit the standard master socket (see Kitz first link) or did he fit an ADSL V10 faceplate with it ?

The second Kitz article deals with DIY troubleshooting, but navigate around the site for more info as to possible causes of interference.

http://www.kitz.co.uk/adsl/socket.htm

http://www.kitz.co.uk/adsl/troubleshooting.htm

If he just fitted the standard NTE5 faceplate, then you can fit an ADSL filtered faceplate yourself which will give better screening and do away with the need for microfilters for either that or any phone extension cables.

http://www.amazon.co.uk/ADSL-Faceplate- ... B0030BC2PW

http://www.adslnation.com/products/

I also use a 2m Hi Speed ADSL cable to connect the router to the master socket which can increase your throughput http://www.ebay.co.uk/bhp/high-speed-ad ... 5573.m2388 and for good measure - occasionally a Cat6 Ethernet cable.
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