Kitz Forum
Broadband Related => ADSL Issues => Topic started by: JohnRYoung on September 19, 2007, 11:57:09 PM
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It couldn't last. Following resolution of my problems described in "Low Profile", I had about two months of stable connection from BT broadband with downsteam sync rates 1700-2000 kbps and SNr margin of 9-15 dB. Now, suddenly, once or twice a day I notice sudden drastic sluggishness. Inspection with DMT.exe (thank you, thank you to the providers of this!!!) reveals that the connection has resynched at >2000 kbps and SNr margin of 6-8 dB, and the crc error rate has gone off scale. Using DMT to resynch at higher SNr margin (>10) restores the effective connection speed and drops the crc error rate. So it appears that someting has been changed in the exchange that has lowered the target SNr too far. Kitz said something about imminent changes by BT, and I wondered if this was one of them. The connection is currently non-interleaved, which may contribute to nthe crc error rate at low SNr? This was the "solution" to the earlier low profile speed problem. My router/modem is Netgear DG834GT. The current profile setting is 1500 kbps. Present connection is 1952 kbps attenuation 58 bD, SNr 11.4, crc error rate low; 60 mins ago it was 2400 kbps with crc error rate off scale, before manual resynch. Is there a way of telling the modem to always ask for the larger SNr margin. or of getting BT to change the target SNr at the exchange? It seems they have responded to many problems with the slow response of the rate adaptive system by now making it vtoo aggressive in speeding up!
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The effects you are seeing are not likely to be due to anything BT have done. They are the typical result of an intermittent noise problem. There's a lot of helpful information about noise problems at http://www.kitz.co.uk/adsl/lowSNR.htm . If there's any audible crackling on the telephone then there's probably a voice fault and you can report it to BT Retail (dial 150). All sorts of electrical equipment can produce interference, so you might consider whether there's any new equipment in your home or nearby.
I don't want to depress you, but with an attenuation of 58 dB you're always going to be vulnerable to this sort of happening.
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Well .... I picked up the phone to see if I could hear a crackle as you suggested, and I heard radio 5 live on it !!!??? Turns out the extension in my bedroom, which I never use, had fallen off its hook.....I left the radio on after I got up this morning .... I rarely use the landline phone, so this may have been the cause all along ..... I am a complete idiot!
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:lol:
Thanks for letting us know.
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..... I am a complete idiot!
Don't worry, you are amongst friends :dance: ;)
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LOL :lol:
Nice one - and all credit for admitting it!!
However..... (serious hat on) - even if the extension in your bedroom had fallen off its hook, it shouldn't have interfered with your broadband! Have you got an ADSL filter on that phone, even if you never use it?
If not, might be time to stick one on there, and on any other telephone connected devices, including sky boxes (they are notoriously bad for causing problems), alarm systems, ALL telephones etc.
Thanks for giving me a laugh this morning though :)
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Filter on everything, but the trend continues. This morning the sync speeed was up at highest yet 2900 kbps, SNRM=6.6, erors off scale, no functional connection. Without DMT I would have no connection at all!
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What ought to happen automatically is that the exchange system will increase your target noise margin to make the connection more stable. It looks as though you're still at the default 6 dB target margin, and I guess it's possible that, by using the DMT tool to stabilise your connection, you're fooling the exchange system into thinking that it doesn't need to do anything. If you can stand a couple of days of hopeless connections, it might be worth resetting the default with DMT (set the value in the modemoptions 00 box to 00) and leaving the automatic process to do its work.
Of course, it could still be worth doing some more investigation to see if you can trace the source of the interference.
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That makes sense. I am trying to see if there is a temporal pattern now. next week I am going to spend a couple of days in hospital, so then I can try that. It has now started dropping the connection completely with huge error rates after being stable for many hours. I guess that is consistent with an intermittent noise source of some kind. Have to look at the radio five schedule ;-)
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Now I am getting really confused. This behaviour seems reproducible - After resynching the router, I get good connection with low error rates for hours, even if I leave it with 6 dB snr margin. Then suddenly get huge error rates and either the snr drops to less than 6 or the router drops the connection completely. But resynching the router at this point always restores a good connection immediately. This morning, it was hanging on at 2300 kbps with snrm=2.3 ... error rates off scale ... then I resynched and got >3000 kbps at snrm=6.3 and low error rate. What gradually accumulation effect, or randomly occurring event, can lead to degradation of the connection that is invariably recovered after a resynch even when the latter is at an increased speed?
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That is rather odd. I suspect that what's happening is that something sets off a short burst of interference which causes the router to go into an unstable mode, even after the interference has stopped. You might consider upgrading the router firmware if a more recent version is available. There's also an unofficial firmware version available from http://dragonslight.altervista.org/ubergt/index.html which is worth considering. When I was using a DG834GT I used this firmware and it was noticeably more stable than the official firmware.
A very short burst of interference like this suggests a dodgy freezer thermostat or something like that, or some fairly powerful electrical equipment starting up.
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Thanks again.
At last I found a way to make the target snrm go up. I use routerstat's alarms to force
up to 10 reboots per hour when snrm went below 6 dB. During the night there were
two occasions with ten successive reboots....then 15 minutes after the second there
was a resynch to give a 9dB snrm, and rebooting now starts at 9dB. So now we will
see if this solves the problem! Synch is now at 2528 kbps and profile up to 2000 ::)
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That could be a good result. Here's hoping!
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>> At last I found a way to make the target snrm go up. I use routerstat's alarms to force up to 10 reboots per hour when snrm went below 6 dB.
Brilliant :D
Fingers crossed for you that it now stays stable. :)
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Gawd, I wish my SNR margin was that insensitive - it seems 2 reboots was enough to push it up from 9 to 12dB :(
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Well, now that I don't have to resynch every hour, I have been able to watch the line with routerstats. I make the following observations.....
The snrm drops precipitately at exactly the same two times each day, 7.50 and 21.40 ... I have the routerstat alarm set to reboot when this happens, but if I leave that off, the connection stays but is unuseable. During the day, the snrm is very stable, but at exactly 17:00 each day, it starts a gradual decline, eventually forcing another reboot between then and the repeatable one at 21.40. After reaching a trough at around midnight, it then gradually rises until the 7.50 interruption. This is all the same during weekdays and over the weekend. I think it is bearable, but I would be interested in any possible explanations for this systematic behaviour. I am pretty sure there is nothing in my house that changes at those times. :-\
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Can I suggest that you see if the times remain the same when the clocks change this weekend? You would expect a gradual decline in SNR once it starts to get dark if you have an overhead line (MF radio propagates further) and there is generally more electrical noise in the evenings anyway - microwaves, TVs etc etc. Off the top of my head I can't think why it should be so regular though - hence the suggestion for this weekend :)
Edit - how close are your neighbours houses and do you know them well?
Edit2 - are you by any chance in an "Economy 7" area where electricity is discounted between 1am and 8am?
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I'm in total agreement with what rizla is suggesting...
You had problems a couple of months back then all went quiet for a while, this could have co-incided with having had a poor/ wet June.. then iirc things were ok for a while again when the weather was warmer. Now it seems to have started up again.
There could be the Economy 7 thing - it could be a heating switch.. how about Lighting?
Florescent lighting is something that also crops up on occasions as being a cause.
Also have you tried the AM radio trick to see if you can pin-point anything with that.
If I were you I'd also ask my neighbours a few questions to see if that brings anything to light (sorry for the pun ;/). Explain that youre having a problem with your adsl and the indications from the trouble shooting so far is that it could be electrical interference from heating/lighting, mentioning the times to them.
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Just to add :
I reckon it is an inductive load as the timing isn't exactly to the hour/quarter hour. That indicates to me that its probably an electromechanical timer switching something on. Now you don't generally come across those very often these days so either something fairly inductive (and "chunky" in power terms) is switching on or we're dealing with something old. eg modern central heating systems will use a digital timer which switches a relay (contactor) remotely - usually wirelessly. Older systems will have an electromechanical timer. Inductive loads have a tendency to weld the contacts closed on most digital timers if they try to switch the load directly.
Hope some of that makes sense :)
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OK, the times of the predictable interruptions are the same after the clock reset....that is to say they occur at the same time of day GMT as they did BST. So that would fit with it being someone's timer IF that timer is also updated. In fact this does seem most likely. The increased evening electrical noise also fits, and yes, I do have overhead telephone AND electricity! That just leaves one thing I don't understand. How is it that the noise spikes, assuming that is what they are, have the effect of a sudden drop in snrm which then remains low (from 0-4 dB) stably until the router is either rebooted or told by DMT to resynch. In other words, how does transient noise lead to stable effect on snrm? And why does it reproducibly return to normal snrm with a resynch? Looks like the noise causes an internal change in the router (or the exchange?) that does not revert when the noise ceases. That surprises me, but perhaps does not suprise others who know more? The evening noise is getting worse as the night get longer, and my profile is getting dropped again ... a sad winter may be on the horizon. :(
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>a sad winter may be on the horizon.<
Stick your head in the gas oven now, to avoid the rush! ;)
I get noise that affects FM radio in short bursts every five minutes, or so. I'm convinced that it is caused by a sewage pump that trips when the storage chamber is full. Trouble is I can't prove it and it would cost me to get whoever it is that deals these things to investigate. Fortunately it doesn't seem to affect my ADSL.
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Got to pop out in 10 mins so just a quick reply :
It sounds to me that your router/modem isn't doing bitswapping correctly. There are implementations of bitswapping which aren't resilient to large impulse noise transients.
Can I just confirm that :
a) The router shows a reduced SNR and will keep that SNR until a resync?
b) The router will return to the "correct" SNR after a resync?
c) The router shows a fairly stable SNR between 2140 and 0750 (doesn't vary by more than 1db)?
I'll have a think about this while I'm out.
PS - do you know your neighbours well, and how close are their houses to yours?
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a) The router shows a reduced SNR and will keep that SNR until a resync?
--- confirmed.
b) The router will return to the "correct" SNR after a resync?
--- confirmed
c) The router shows a fairly stable SNR between 2140 and 0750 (doesn't vary by more than 1db)?
--- not quite. It is very stable from 0750 to about 1600 (was 1700 before clocks back, so it's when
it gets dark). Then it starts to drop gradually while also showing increased short-period fluctuation
(about 1.5 dB up and down from drifting mean). The drift is <= 1 dB per hour and continues till
about 2000-2200. I have routerstats set to reboot after 60 seconds at <8 dB (otherwise it becomes
unuseable). This causes one or two reboots between 1700 and the 2140 even. After midnight, it
gradually increases again until the 0750 event. Attached is a tif file with a "typical" 24hr routerstats
graph, with approximate synch speeds underneath the snrm trace.
I'll have a think about this while I'm out.
PS - do you know your neighbours well, and how close are their houses to yours?
--- well enough on a good day if I am feeling very tactful :-X
--- I am the very small middle of a 3-house terrace :-\
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The graph is about what I'd expect now that the nights are getting longer.
I think you're going to have to go and have a word with your neighbours - mention the times (0750 and 2140) that it happens and see if there's any reaction. Mention that you're probably going to have to get BT out to locate the problem and they will be looking for someone to bill for the work so its in everyone's interests to sort it out prior to that.
If you can find a broadcast radio station (one of the BBC ones preferably) which has noticeable interference at the times mentioned then you can get something done about it. If not then whoever is causing the interference can just ignore BT/you/whoever. I suspect that given what you've said about having to reboot at <8dB you will find that there IS interference noticeable between 2140 and 0750 but the time of year will make it difficult as MF stations tend to fall apart after dark.
It strikes me that the timing is very odd indeed. I doubt it would be central heating as keeping it on either all night (2140-0750) or all day (0750-2140) isn't normal - even for someone as far north as you*. Best not to speculate what it is until you have a word with the neighbours.
*I'm assuming from the time you say it gets dark that you're in Scotland. I used to live way way up north (Western Isles) you see, so I remember 5-6 hours of daylight in winter :)
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And finally .... since the last weekend, the repeatable timed inerruptions have stopped and I have had a stable connection since then. Central heating now on all day? Telepathic neighbours? No need to speculate any more, but maybe it will come back in the spiing. I will let you know. Until then, I think we can let this thread fade into obscurity, but only after I have again thanked all those who were kind enough to consider my problem. Thank you. ::)
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Glad its sorted - for now at least. If the problems do start up again I'd appreciate it if you could let us know as I have a theory about the cause of this. I'd need accurate timings & dates to be sure though :)
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Im glad that it seems to have sorted and lets hope it stays that way [need a fingers crossed smiley]
Out of interest did you make any subtle enquiries with your neighbours?
>> I have a theory about the cause of this. I'd need accurate timings & dates to be sure though
>> If the problems do start up again
Yes indeed -please let us know John how it goes.
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No communication with neighbours at all, unless they happened to read this forum ... if they were having the same problems :-X
However, although the abrupt repeatable interruptions have indeed gone away, I do still seem to get a terminal fall-off in snrm every evening starting about 3:30 pm which usually means I have to resynch to get an effective connection. Critical point seems to be about 8dB. Default on connection has reverted to 6dB - so I am dependent on DMT again. Don't know if any of that affects your theories :-\