Kitz Forum
Broadband Related => ADSL Issues => Topic started by: SlowConnector on August 12, 2012, 03:17:42 PM
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You may recall I had some problems (http://forum.kitz.co.uk/index.php/topic,11208.0.html) 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 (http://www.kitz.co.uk/adsl/rein.htm)) 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 (http://www.techradar.com/reviews/pc-mac/monitors-and-projectors/monitors/samsung-syncmaster-s27b750-1087922/review)), 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 (http://www.expertreviews.co.uk/wireless-routers/1283365/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
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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
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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 (http://www.vwlowen.co.uk/internet/files.htm#routerstatslite), 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?
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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 :o
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.. (https://docs.google.com/folder/d/0B6wW18mYskvBZWM5OTY5NWMtMjQ2ZC00OTQ1LTg5YWUtODA1NmZkYzg5ZGVj/edit)
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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?
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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.
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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.
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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...
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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)
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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?
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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?
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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 :-)
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What is a CP? Do you mean ISP (Internet Service Provider)?
CP == Communications Provider (Telephony and Internet services).
ISP == Internet Service Provider
:)
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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 :'(
(https://forum.kitz.co.uk/proxy.php?request=http%3A%2F%2Fwww.comedy.co.uk%2Fimages%2Flibrary%2Fpeople%2F180x200%2Ff%2Ffather_ted_jack.jpg&hash=96a89e64d09644dda8254feb7d15f800ba20b66b)
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:lol:
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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 :-)
I wouldnt go with the 3db profile, it will cause problems even on short circuits cant say i have ever seen one work well 6db is the standard and best speed/reliabilaty factor. gunjack the snr target is set from the isp or managed my bt wholesale so would be 3db which ranges to 6db 9db 12db & 15db settings so your tweakable router will have no impact on the profle it may achieve a higher sync speed than stock isp routets like our testers.
Your speed is good any way at 11 meg, much better than mine which is super tuned may i say :graduate: but a long line @ 4 meg with street average <2 meg.
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I wouldnt go with the 3db profile, it will cause problems even on short circuits cant say i have ever seen one work well 6db is the standard and best speed/reliabilaty factor.
If the line has been troublesome in the past, then I'd tend to agree with GJ and Johnny... Id make sure the line was rock steady at 6dB before going any lower.
cant say i have ever seen one work well
@Jonny - heres one for you for you to look at, just so you know it can happen :) Pretty boring... practically flat-lines at 3dB for the past 4+yrs.
(I do have a slight problem but its not SNRm related - more to do with a sloooooow deterioration of the line, but BToR would laugh their socks off if I called them out about it :/ )
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do you not get any crc's with that 3db profile your sync speed is good ;) but 3db doesnt have enough difference for a reliable workplace or critical connection.
Also the other thread on the thunderstorm affecting the fttc snr, have you noticed a dip on the snr during a thundersorm on your asdl2+ connection?
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Nope, hardly any CRC's ever. 0 errors in the past 24hours.
Sync speed is Annex_M which means that I have given a chunk of my downstream tones to the upstream.
4 yrs ago I used to be able to sync at 24/2.6, but over the past 3yrs the line has gone through a very slow decline.
If I wanted I could probably tweak the line down to 2dB and it would still hold - in fact I did that ages ago as an experiment and it was fine for several weeks.
>>have you noticed a dip on the snr during a thundersorm
Thats why I said "practically flat-lined".
Thunderstorms are one of the few things that affect the SNRM and CRCs, but touchwood in all that time its never lost sync through one. I did have some weird problems yesterday (link (http://forum.kitz.co.uk/index.php/topic,11701.0.html)) but that sorted itself by tea-time, which is the only reason why RS is now running so I can see if it was just a one off - which it appears to have been.
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Nope, hardly any CRC's ever. 0 errors in the past 24hours.
Sync speed is Annex_M which means that I have given a chunk of my downstream tones to the upstream.
4 yrs ago I used to be able to sync at 24/2.6, but over the past 3yrs the line has gone through a very slow decline.
If I wanted I could probably tweak the line down to 2dB and it would still hold - in fact I did that ages ago as an experiment and it was fine for several weeks.
>>have you noticed a dip on the snr during a thundersorm
Thats why I said "practically flat-lined".
Thunderstorms are one of the few things that affect the SNRM and CRCs, but touchwood in all that time its never lost sync through one. I did have some weird problems yesterday (link (http://forum.kitz.co.uk/index.php/topic,11701.0.html)) but that sorted itself by tea-time, which is the only reason why RS is now running so I can see if it was just a one off - which it appears to have been.
You must stay in the exhange then ;D or next door why bother with fttc if your adsl2 is that solid?
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My apologies to SlowConnector for perpetuating the hijack of his thread but I think it might be interesting to show the Sync Speed and SNRM graphs for my line so that the latter can be contrasted with that of Kitz, above.
According to the Beatie dbase, my line is 2481 metres from The Cattery to the exchange (EABSE). When I measured the distance, electronically with a Hawk, it was a maximum of 2164 metres (corrected for the test leads).
I am using an unlocked Huawei EchoLife HG612 as a modem/router to make use of its Broadcom 6368 chip. My CP is TalkTalk and the line is configured for a target SNRM of 6 dB with the DLM switched off. Having watched the 24 hour cycle of the SNRM for a number of weeks, I tweaked the DS target SNRM to 4 dB, thus gaining about 1000 kbps in DS Sync speed.
Like Kitz, I have a boring flat-line graph -- not for SNRM but for Sync speed! My typical SNRM graph is quite a mess -- see below. All said and done, I have been running like that for at least a couple of months without a single loss of Sync event. ;D
I wouldn't advise doing what I have done to the average end-user but being a techno-cat, I fully understand the consequences and the possible events that might occur. (If my SNRM graph was just that bit cleaner, I would have tried with a 3 dB target. :angel: )
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I wouldnt go with the 3db profile, it will cause problems even on short circuits cant say i have ever seen one work well 6db is the standard and best speed/reliabilaty factor. gunjack the snr target is set from the isp or managed my bt wholesale so would be 3db which ranges to 6db 9db 12db & 15db settings so your tweakable router will have no impact on the profle it may achieve a higher sync speed than stock isp routets like our testers.
Sorry jonny, but you're off the mark there.... some points:-
1. yes, the initial snrm is set by TT profile, however using a DSL-2640B (6348 chipset) and DMT it is easily tweakable to almost anything you like.
2. TT LLU does not use any BRAS profiling
3. TT's DLM can be permanently disabled on your line if you ask, me and Mr. b*cat are testament to this.
4. my 50dB line is very stable, so I tweak down to 2.5dB peak in daylight, it troughs around 0.5-0.7dB in the small hours, for an extra 1000-1200kb/s sync. I don't get any loss of sync at those rates, yes I get several hundred CRC's in a 24-hr period but on a 64 depth Interleaved line it doesn't cause any problems.
5. I constantly get around 85% throughput, so no probs there.
On the above basis, hence why I suggested the OP tried to tweak down for some extra speed if the line is stable enough to support it. There are many people who's line can support lower than 6dB snrm, but I suggest that the vast majority would never have understood let alone tried it, and forums such as this help spread the word ;)
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When I moved to BT-based ADSL2+ early this year, DLM quickly put me on a non-interleaved 3 dB profile, and it was stable for months in spite of the high error rate. So I agree with GJ that it depends on the particular line, but can be entirely satisfactory. Unfortunately in my case, a temporary intermittent line fault caused DLM to respond aggressively, but if this hadn't happened I'm sure I would still be quite happy with a 3 dB target SNRM.
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My BT ADSL2+ line also runs quite happily at a 3dB downstream target interleaved at depth = 64 and always has ever since being converted to 21CN.
SNR margin trace is flat during the day - the intial connection appears to always be around 3.3 to 3.5 rather than exactly 3.0
Line reported D/S Attenuation is 36.5, sync is usually around 13900 to 14100.
D/S margin drops to around 1.0 during the evening (always lowest curiously at 9.30pm) and yes the CRC errors do mount up overnight but then I'm asleep during that period! I suppose if you do a lot of overnight downloading it might cause problems.
During the day although the FEC corrected errors are still accumulating the CRC's are pretty well zero so I can nearly achieve the IP setting during speed tests.
(Typical ping times from the command prompt are around the 28 to 30 mark with jitter being 1ms)
I did have a fault once which caused the DLM amongst other things to raise the target to 6. Once the fault was cleared the DLM monitored the line for I think 2 days.........and promptly reduced the target back down to 3 again.
I have got a Routerstats trace somewhere of a thunderstorm going through where the CRC's and ES go bersek and the SNR margin drops to next to nothing/zero, line still holds in sync quite happily though actual throughput reduces to zero. Once the thrunderstorm passed all reverted to normal. No re-sync events, no drama etc.
So yes it does very much depend on the line and the quality of the house wiring and lack of external interfereces REIN,SHINE etc but quite possible to run at a 3db target continuously.
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I think the general consensus is that if you know your line then 3dB can work quite well. B*cats graphs show that hes well aware of the normal fluctuations of his line and by tweaking it hes been able to get the best speed whilst still maintaining a stable line.
The BTw DLM can sometimes be a bit of a pain when it kicks in, but since most LLU providers dont have DLMs that work in the same way as BTw's then those users can tweak with less caution than someone on a BTw based line.
I can see where youre coming from Jonny in that most users wouldnt have a clue how to get the best and optimise their lines, but the 3dB can and does work well for many.
Just FYI (I dont know if you are aware), but the reason why 6dB used to be the default goes back to legacy adsl when a minimum of 2 bits per tone was needed to load that particular subchannel during the sync up phase. ADSL2,2+ only needs 1 bit. Since each bit requires 3dB of SNR - adsl1 needs 6dB whilst adsl 2+ only needs 3dB to load the subchannel.
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Well, I never knew that Kitz. Keep feeding me please. :graduate: ;D
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Well, I never knew that Kitz. Keep feeding me please. :graduate: ;D
yw BS.. theres a lil bit more info on the topic under bitloading (http://www.kitz.co.uk/adsl/adsl_technology.htm#bit_loading).
It should also be noted that the old fixed rate lines - ie true fixed rate 512/1Mb/2Mb and not capped rate rdsl which is used now - didnt utilise Target SNR Margins, which is why a longish line would either sync at a straight 2048kbps.. or it just wouldnt sync at all.
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So far, the 6db profile seems to be rock steady, just like the 9db and 15db profiles, but I am still tempted to ask my ISP for the 3db profile just to see what the best connection for my line is.
Now that the source of RFI/REIN in my flat has gone away, the SNR does not seem to fluctuate at all. There was a thunderstorm in our area soon after I moved to the 9db profile, but it had no effect on the stability of my connection. The only thing I noticed was that the lightning registered as tiny ripples on my SNR graph.
Two things have supprised me so far: firstly the changes to my connection profile (15db then 9db then 6db) doesn't seem to have increased the sensitivity of line to line noise, as the connection has not dropped once. The SNR for my line has remained stable with each profile change.
Secondly, I am suprised how little gain in download speed has been achieved by changing profile. At 15db, I was getting a download speed of just under 8Mbps, and with the new profiles, it has improved, but not by huge amounts (9db gets 9Mbps, 6db gets 10.5 Mbps). Based on my experience to date, I am not sure there is going much gain from a 3db profile, but I will ask for it anyway.
Talktalk say that it is possible to achieve 30Mbps their ADSL2+ package if your line allows, but I think this is just bluster. It would be interesting to know what percentage of their subscribers actually achieve anywhere near this level of performance. My guess is that less than 1% of their subscribers get anywhere near 30Mbps.
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I wouldnt go with the 3db profile, it will cause problems even on short circuits cant say i have ever seen one work well 6db is the standard and best speed/reliabilaty factor. gunjack the snr target is set from the isp or managed my bt wholesale so would be 3db which ranges to 6db 9db 12db & 15db settings so your tweakable router will have no impact on the profle it may achieve a higher sync speed than stock isp routets like our testers.
Sorry jonny, but you're off the mark there.... some points:-
1. yes, the initial snrm is set by TT profile, however using a DSL-2640B (6348 chipset) and DMT it is easily tweakable to almost anything you like.
2. TT LLU does not use any BRAS profiling
3. TT's DLM can be permanently disabled on your line if you ask, me and Mr. b*cat are testament to this.
4. my 50dB line is very stable, so I tweak down to 2.5dB peak in daylight, it troughs around 0.5-0.7dB in the small hours, for an extra 1000-1200kb/s sync. I don't get any loss of sync at those rates, yes I get several hundred CRC's in a 24-hr period but on a 64 depth Interleaved line it doesn't cause any problems.
5. I constantly get around 85% throughput, so no probs there.
On the above basis, hence why I suggested the OP tried to tweak down for some extra speed if the line is stable enough to support it. There are many people who's line can support lower than 6dB snrm, but I suggest that the vast majority would never have understood let alone tried it, and forums such as this help spread the word ;)
I was assuming a BTW circuit, thats great if you can tweak it to suit yourself although it seems like a lot of effort for little gains?
Yes the throughput should be roughly 85%, good put 82%
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>>> doesn't seem to have increased the sensitivity of line to line noise,
The Target SNR(m) is basically a buffer zone to allow for fluctuations.
When graphing a line you would expect exactly the same fluctuations and blips and curves regardless if it was on a 6dB or 9dB profile.
Taking B*cats graph as an example, we can see that over the course of a standard day his line fluctuates between 5dB and 1dB = a 4dB daily variance. If he had a 9dB profile, then the graph shape and fluctuations would be practically the same, only it would be graphed in the 10-6 dB region, rather than the current 5-1dB.
What you would expect to see however is that the error count on that line will increase the lower the buffer zone goes. The more errors (CRC/HEC/ErrSec) you get then the more likely you are as an end user to see things like slower 'real time' speeds due to data having to be re-transmitted. The nearer to 0dB you go, then the more errors will rack up.. including the more serious errors which will cause the line to drop completely.
>> I am suprised how little gain in download speed has been achieved by changing profile
This is were attenuation comes into play.
Sync speed depends on the individual subchannels and bit loading during channel analysis at sync time. Although we can say on average each 3dB of SNR is 800kbps, you have to bear in mind this is an average and the reality can be anywhere 400-1200kb.
A 40dBm atten line isnt ever going to be able to load all of the adsl2+ subchannels available, therefore the effects of these profile changes will be far less than say someone with a 10dBm line who will be able to utilise all of the bins. The less bins that are loaded, then the less effect it has on the sync speed.
Your line (40dB) is atm syncing at the high realms of its possibilities.
>> Talktalk say that it is possible to achieve 30Mbps their ADSL2+ package if your line allows, but I think this is just bluster.
Not only is that bluster, its technically impossible. Even if your line was able to load every single bin with the maximum 15 bits, adsl2+ just does not have enough subchannels to support 30Mbps. 24Mbps is the limit. :/
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Thanks for explaining, I understand how the attenuation place a cap on my download speed.
However, I am not sure I understand whether line attenuation recorded by my router is fixed (by my distance from the exchange), or whether it varies with my IP profile, as I note that line attenuation for my connection seems to vary between 33-40db.
If I understand correctly, when I was on a 15db profile, line attenuation was about 35db, so if I went to a 6db profile, then attenuation on my line was reduced to 40db as recorded by my router.
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Attenuation is a value which is calculated by the router, based on the conditions which exist at the time. It's a sort of average of the attenuations of all the individual tones which make up the ADSL signal, but it's possibly also weighted to take more account of the tones which have high bitloading than those which have low bitloading. So when you upgrade from ADSL to ADSL2+ (for example) higher frequency tones are used, which results in a higher average attenuation.
when I was on a 15db profile, line attenuation was about 35db, so if I went to a 6db profile, then attenuation on my line was reduced to 40db as recorded by my router.
You mean 'increased' I presume. :) This could be accounted for by the fact that, on the 6 dB profile, more high frequency tones were in use.
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Line attenuation is relative to the loss of the dsl signal on your pair. The longer the line is the higher the attenuation, other factors come into play like the gauge of the conductor and quality of pair.
Also if your unlucky you may even have some aliminum in your pair which again will increase loss.
The 'E' side of your pair will have the biggest affect on this.
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>> I understand how the attenuation place a cap on my download speed.
Its not that attenuation places a cap, attenuation gives an indication of the physical condition and length of your line from the exchange. The longer the line then the more attenuated the line will be ie the signal strength is reduced. Think someone shouting across a crowded room, the further you are away from that person the less chance you have of hearing what they are saying. You could say in very simplistic terms that Attenuation is a measurement of the amount of signal deterioration.
>>> I note that line attenuation for my connection seems to vary between 33-40db.
Attenuation as reported by your router can vary slightly for a few different reasons.
1) Some routers report attenuation at a specific frequency.
2) Some routers report attenuation across what tones are in use.
3) Some routers report attenuation across all tones that are available for use.
Therefore its not unusual to see slight increases in attenuation as your sync speed increases. However Ive just noticed your line was reporting 40dBm when on the 8Mb 15dB profile (first post).
If you want a little bit more info theres some here:-
What is attenuation (http://www.kitz.co.uk/adsl/linestats.htm#attenuation).
Decibels in the context of adsl (http://wiki.kitz.co.uk/index.php?title=Decibels)