Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[SlowConnector]

You may recall I had some problems with my Talktalk ADSL connection: I called in a BT engineer, but they could not find any fault with the line. Eventually I discovered that the cause of the problem was Rado Frequency Interference (RFI/REIN) from my LCD monitor, which reduced the noise margin from 18dB to 12dB.I found a work around by training my monitor to run at a lower connection speed (5.5Mbps instead of 8Mbps) that was stable with the lower noise margin.

To get rid of the RFI, I bought a high end monitor (Samsung S27B750V), but now my connection is even more unstable for some reason. When I start my router, the noise margin is in the range of 14-18dB, and the connection speed is between 5.5-8Mbps. However, the connection does not remain stable for more than 3 minutes at a time (just enough to post this message). The attached graphs of the noise margin and connection speed look like the Manhattan skyline because the connection goes up and down in an almost regular pattern.

I have run the router while my new monitor is turned off at the mains, so I sure that the monitor is not the source of the problem. Any idea what else could be be the cause of the connection dropping?


ADSL STATISTICS

Router: D-LINK  DSL-2680
Mode:   ADSL2 PLUS
Type:   ANNEX_A
Status:   Showtime

Downstream/Upstream statistics
Rate (Kbps): 8504 kbps / 411 kbps
 
SNR Margin (dB):   14.4 / 19.3
Attenuation (dB):   40.0 / 21.3
Output Power (dBm): 0.0 / 11.3
 
Super Frames: 11500 / 11501
RS Correctable Errors:   719 / 4
RS Uncorrectable Errors: 8 / 1
 
HEC Errors:   260 / 0
Total Cells:   44457 / 32890
Data Cells:   13139 / 6483
Bit Errors:   0 / 0
 

[asbokid]

Does the Huawei HG532 have a telnet interface, to get the raw line statistics?  Specifically can you get the QLN (Quiet Line Noise) dataset.   QLN provides a crude spectrum analysis of the frequencies used for the DSL subcarriers. It sweeps through from DC to 2.2MHz in 4.3125kHz steps,  and measures the noise on each subcarrier.  This is done only at sync time, so sporadic noise is not captured, but it could be a basis for identifying the nature and origin of the interference if that is what it is. 

Are there any audible symptoms in the voiceband to suggest a line fault beyond your premises?   Crackling, hissing, spitting?

cheers, a

[SlowConnector]

Apologies if my post was unclear. I stopped using the Huawei EchoLife HG520b because this router does not allow me to collect statistics continuously using Router Stats Lite, which I think means that it does not have a telnet interface. For this reason, I switched to using a D-LINK DSL-2680 that does allow the statistics to be collected continuously, and these are the statistics shown above.

I don't think there are any problems with the phone line that are audible, but maybe I am just used to the line that we have. What software would I need to obtain a QLN dataset?

[asbokid]

Hi SlowConnector,

My bad, I didn't read the first thread properly.

Not much can be done with the DLink DSL-2680. They run the proprietary ZyNOS operating system, and ZyXEL's RAS - router application software.  There is a telnet shell of sorts but it's quite limited. The DSL-2680 is based on the Trend Chip TC3162U, a single MIPS32 core CPU, with a TC3086 DSL front end and line driver.  They generally synchronise at a decent speed but don't seem very reliable.  The links about the DSL-2680 in the ThinkBroadband thread, below, are mostly broken now - since Trend was bought out by Ralink and then swallowed up by MediaTek 

http://forums.thinkbroadband.com/talktalk/3968810-talktalk-router.html#Post4015376

If you have a Broadcom-chipset modem knocking about, they usually provide the most diagnostic information.

cheers, a

EDIT:  The datasheets, manuals, photos, f/w images and flash dumps for the DSL-2680 and DSL-2780 have been collected together here:

https://docs.google.com/folder/d/0B6wW18mYskvBZWM5OT..

[SlowConnector]

I don't have access to a Broadcom router, so it won't be possible to obtain the diagnostic information you have requested. This is a pity, because the method of QLN diagnosis that you have suggested looks very promising.

Good news! For some reason, the interference on the line seems to have stopped on Sunday evening. The ADSL connection seems to have stablised at 8.5Mbps, and the SNR is a constant 14dB. I don't know what has changed or whether this situation will continue for long, but I will keep you updated. However, if anyone can interpret or recognise the pattern of interference shown in router stats (above), I would me most interested to hear from you.


Additonal thoughts:

• Looking at the noise margin chart, one thing has occured to me, that the noise ratio is a combination of two things: noise on the line relative to signal strength;
• Until now, my problem has been noise on the line caused by my monitor, but since I replaced my monitor, noise on the line should no longer be a problem;
• If the noise is gone, then could the connection drops be attributable to the signal strength going up and down?
• If the signal strength is changing, what could cause this to happen, assuming there is no change in the hardware configuration. Could a weak signal be something that might be caused by changes at the BT exchange (DSLAM)?

Alternatively, could my ISP have changed any of my router settings that would have resulted in the router being unable to pick up the signal properly?

[SlowConnector]

I think I have found the source of the RFI that has been causing my connection to drop, and once again I just can't believe it 

On Monday evening, the extractor fan in my bathroom gave up the ghost and died after an honourable service of 8-years. It has not been running very well recently, and the amount of noise it was generating had been increasing steadily over the last few months. I think the electric motor had started to "stick", i.e. the motor would periodically grind to a halt, and then restart a little later.

Before the extractor fan stopped for the last time, my connection dropped. I don't have 100% proof that the fan was the source of the interference, but since it has been turned it off at the mains, there have been no other connection drops. I am not certain a small electrical motor could be a strong source of Rado Frequency Interference (RFI/REIN) that would cause my router to drop its connection, but my guess is that the extractor fan malfunction was the culprit.

[burakkucat]

How interesting! 

It just goes to show that nothing should be discounted and everything should be regarded with a degree of suspicion -- until proven free from blame.

Please keep us updated with your observations, etc, over the coming days / weeks.

[Ezzer]

I reckon Monitors were responsible for about a third of REIN faults I came across. Just because you come across one cause of a fault dosnt mean there isnt a second lurking around anywhere. And in your case who knows if the cause of both could have been related. One surging the other or both affected by the same surge.

When you think of how many electrical sources we're surrounded by...

[SlowConnector]

Now that the source of the RFI has gone away, I have moved on to a faster profile, from 15db to 9db and my connection has been rocksteady. Download speed is now up to 9Mbps, which is a huge improvement to the 3Mbps I was getting back in February.  8)

[Jonnyteg]

A very good case of REIN and symptoms as the SNR showing this by going to 0db     well done in finding the source yourself, many end users fail to believe this can happen.   

Why not speak to your CP for a 6db downstream profile for more speed they can apply interleaving if need be if the 6db causes errors?

[SlowConnector]

What is a CP? Do you mean ISP (Internet Service Provider)?

As suggested, I have requested a 6db profile, but there is only a marginal improvement in download speed, which is now up to 10-11 Mbps . Is there a better profile than this, or anything else I can ask for to get a better connection?

[GunJack]

10-11 meg is bob-on for your line attenuation, only way to squeeze a very small extra amount out of it would be to use a tweakable router and reduce your snrm to 3dB-ish, but you'd have to watch for stability if you did this :-)

[burakkucat]

What is a CP? Do you mean ISP (Internet Service Provider)?

CP == Communications Provider (Telephony and Internet services).
ISP == Internet Service Provider

 

[SlowConnector]

Thats OK then. I thought CP might refer to Catholic Priest, which would have been a problem, since I have not been to confession for years 

[burakkucat]