Kitz Forum
Broadband Related => Broadband Technology => Topic started by: roseway on February 07, 2009, 10:50:20 AM
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This morning about 10:30 I believe that I saw my target noise margin drop automatically by 3 dB.
Some time back I had a lot of problems with an intermittent line fault, and my target noise margin was bumped up to 15 dB. But for the last few weeks my connection has been exceptionally stable and with low error rates. I'm using a DG834GT with the DGTeam firmware, and I tweaked the target noise margin down to the lowest value it would go to, which was about 9.5 dB. After two weeks of uptime with only very small variations in the noise margin over the day and night, this morning the connection suddenly dropped and it immediately reconnected with a noise margin of 6 dB. The only explanation I can see is that the target noise margin has been lowered by 3 dB.
You can see a routerstats snapshot below.
[attachment deleted by admin]
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I'm sure you're on the case, but after a day or two (assuming it stays like that) you need to change the % setting in DGTeam to be "gentler" so that it syncs with a slightly higher margin (say 7, 8 or even 9dB) as the next 3dB step may take you into unstable territory and undo everything before you notice.
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Yes, that was my plan. I'll probably set it back to 9 dB, which should hopefully give me the same stability as I've had for the last few weeks and eventually trigger another reduction.
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I'm particularly interested in how you get on as it's very relevant to a good friend of mine who I'm helping.
He had truly awful internal wiring, probably some from the 1930's and was running below 2mbps.
After sorting this all out he now gets about 6mbps but has a "stuck target margin" at 15dB.
Despite repeated calls to BT (and internal assistance from a forum member elsewhere who works for BT) they have failed/refused to reduce the target. They did however agree to turn interleaving off which got some extra speed.
So he then took to using DMT to force a faster sync and gets over 7mbps, though obviously it starts at a lower figure.
However, a few days ago I flashed his router (DG834GT) with DGTeam firmware and it now syncs straight off at about 7700kbps and typically just over 9dB. Whether this will ever improve we don't know, hence the interest in your progress. ;)
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I'll certainly let you know what happens.
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All right for some, then? ;)
After too many resets one day late last summer, I fought tooth-and-nail with Demon to get mine reset from 15dB to 9dB and, eventually they did, last September or thereabouts. 48 hours later (possibly to the minute, curiously), it retrained itself at 15dB again and has stayed there ever since.
I now tweak it using the CLI of the DG834GT, which seems to allow up to -6dB relative to target. Although it's happy tweaked to -6 (9dB at sync), I've settled on a -3dB tweak (12dB at sync) for extra stability, and to ensure that if DLM did reduce the target, I'd still sync at 9 which I know to be stable (I'm not so sure 6 would be stable). I live in hope, week on week, and month on month, that one day I'll check and find it's resynced at 9, but it just doesn't seem to happen.
On theory I have is that, because my line is so much improved (just by cutting the bell-wire) since the 10-day period, DLM can increase the target without me getting anyware close to my FTR. And just maybe, because I'm syncing at a long way above my recorded FTR, DLM is less inclined to give back my margin.
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On theory I have is that, because my line is so much improved (just by cutting the bell-wire) since the 10-day period, DLM can increase the target without me getting anyware close to my FTR. And just maybe, because I'm syncing at a long way above my recorded FTR, DLM is less inclined to give back my margin.
I don't really think that DLM is that devious. But automatic lowering of the target noise margin is not a well documented process, and certainly depends on a number of factors including error rates, not just connection stability. I think it's far more likely in your case that the error rates are above the level needed to trigger the reduction.
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I'm not covinced, I see about 500-800 CRCs, and maybe 3-4 SES errors per day. It's not reconnected once since well before Christmas, bar the very occasional time I force it manually, it's certainly had several runs of 2-3 weeks continuous sync. That's not too bad, is it?
And there is that BT patent application I link to some time ago, which may or may not describe the current DLM. That patent suggests FTR is taken into consideration by DLM in management of target margin...
http://www.freepatentsonline.com/EP1953959.html
BTW - if anybody ever plucks up the enthusiasm to read that paper, the main thrust of the patent seems to be the process of identifying whether the router has retrained ten time in an hour. Put another way, they've patented an algorithm for counting to ten. :lol:
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:)
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Thanks for reporting those observations eric. Do you know an approx timescale how long it took overall?
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The router uptime was just about 14 days, and prior to that I had changed routers and done a bit of fiddling which included some reboots, so I think that the relevant period was just the 14 days of continuous sync with a low error rate.
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Thanks eric
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It's certainly not the first time I've heard suggestions of 14 days being a significant threshold (with error rates relevant too, of course). I've tried monitoring mine on 15 day boundaries (to remove ambiguities about whether the 14s inclusive or exclusive), but no joy - as Eric points out, it 's most probably down to my error rates. Then again, I've set a relatively tame margin of 12dB compared with the 9dB it was to begin with, so my error rates ought to have improved, yet still it doesn't change.
Ooops, I butted in again. Sorry if I always seem to seize upon any debate about target SNRM, it's become a bit of a special interest for me. In fact it was after noticing my actual margin (I didn't know about 'targets' then) had suddenly increased that fateful day summer that I embarked on a crusade to find out why, and to learn a bit more about how ADSL actually worked, and that's what brought me to the kitz forums in the first place.
Now that I'm here of course, I reallise there's so much more for me to enjoy, as well as target SNMR debates ;)
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>> Ooops, I butted in again.
Not at all - you have some interesting observations of your own which you validly bring into the conversation :)
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At 10:30 this evening my target noise margin dropped by another 3 dB. There have been a couple of random re-syncs during the last couple of weeks, so clearly a continuous connection isn't needed; but the error rate has been consistently low (about 2 errored seconds per hour) and this appears to be the main requirement.
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At 10:30 this evening my target noise margin dropped by another 3 dB. There have been a couple of random re-syncs during the last couple of weeks, so clearly a continuous connection isn't needed; but the error rate has been consistently low (about 2 errored seconds per hour) and this appears to be the main requirement.
That's interesting.
It's also interesting that it seems to reconnect automatically after a drop, so there's no need to manually reconnect once in a while (with the risk of appearing even less stable) to "see if it's changed yet", as I had believed to be the case?
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Yes, on both occasions there was a re-sync which had no apparent reason from my side, so I'm assuming that it was triggered from the other end when the target was reduced. I can't say that for certain though, but it seems likely.
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so clearly a continuous connection isn't needed; but the error rate has been consistently low (about 2 errored seconds per hour) and this appears to be the main requirement.
Thanks for that eric, I had seen mention of this before... and therefore thanks for confirming the first hand situation that you experienced.
there was a re-sync which had no apparent reason from my side, so I'm assuming that it was triggered from the other end when the target was reduced.
The auto resync is an interesting observation.
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At about 15:00 my connection re-synced and came up with a further 3 dB drop in the target noise margin. It's now fallen all the way back to the default 6 dB. I've set the noise margin tweak value back to 100% (i.e. no tweaking).
The 3 dB drops occurred at just over 14-day intervals, so that certainly seems to be one of the parameters, together with a low error rate. This all tends to confirm that the oldish patent document which 7LM discovered ( http://www.freepatentsonline.com/EP1953959.html ) does in fact describe the process.
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>>> It's now fallen all the way back to the default 6 dB.
YAY :thumbs:
>> The 3 dB drops occurred at just over 14-day intervals, so that certainly seems to be one of the parameters, together with a low error rate. This all tends to confirm that the oldish patent document which 7LM discovered
Thank you ever so much eric for recording your observations :)
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I have been getting these as well and I am also using the DGteam firmware.
Set at 110% Noise Margin 7 Connection Speed 6,500
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Your stats look very similar to mine. I've certainly found that the DG834GT with DGTeam firmware seems to be an exceptionally stable combination on my line.
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One thing that worries me about all this might (note:'might' as I'm only speculating) be...
The evidence suggests that Eric's 2 ES per hour is categorized as 'very stable'. We've no way of knowing where they draw the line wrt error rates and the 'very stable' category, but taking my own line as an example, I tend to get several hundred ES per day and I've given up all hope of ever seeing a target reduction, and that's with an effective target that's tweaked to around 11-12dB.
But forgetting about my specific line, and thinking about the general case... how likely is it that a long line (say circa 55dM attenuation) is ever going to get error rates like Eric's, even with SNR margin of 15dB...? And hence how likely is such a line will ever get a DLM target reducion?
...which leads to my concern that we might have a situation where DLM would be a one-way ticket for long lines. The 'instability' of ten resynchs in an hour gets you promoted to a high margin, but there may be very little chance of ever satisfying the 'very stable' criteria that gets it reduced again, ot at least not beyond the initial reduction from 15 to 12.
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I think your concern is probably well founded. But there is a proposal to give users the capability to manage their own target noise margin to a certain extent. There's a discussion about it here. (http://forum.kitz.co.uk/index.php?topic=4356.0)
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I think your concern is probably well founded. But there is a proposal to give users the capability to manage their own target noise margin to a certain extent. There's a discussion about it here. (http://forum.kitz.co.uk/index.php?topic=4356.0)
Thanks for that link, I'd somehow failed to spot that entire discussion. Fascinating stuff.
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Hello all
Just found this thread and found it interesting reading, however much went above my head.
With regards to the DG834GT and TeamDG firm ware and SNR margins, I make the assumption your talking about the advanced ADSL settings tab ?
I have looked, but not made any changes here. I would be interested to know what settings you have found work well under this tab.
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What setting you use depends on where you're starting from. If you set the slider to the minimum position (1%) it reduces the target margin by about 5 to 5.5 dB. So if you're already at the default of 6 dB, then using this setting will almost certainly make your connection unstable. But if previous events have resulted in your target noise margin being increased to the maximum 15 dB, then the minimum setting on the slider will bring it down to about 9.5 dB which make a big improvement in your connection speed without seriously risking stability.
An in-between setting of 50% on the slider reduces your target noise margin by about 3 dB, which will give you maybe 400-600 kbps increase in your connection speed.
So if you want to have a play with the slider, what you really need to do is experiment with fairly small changes at a time. But don't do it too frequently (not more than once an hour, I suggest) otherwise you are likely to cause DLM to flag your connection as unstable, and raise the target margin further.
[Edited for English :) ]
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What setting you use depends on where you're starting from. If you set the slider to the minimum position (1%) it reduces the target margin by about 5 to 5.5 dB. So if you're already at the default of 6 dB, then using this setting will almost certainly make your connection unstable. But if previous events have resulted in your target noise margin being increased to the maximum 15 dB, then the minimum setting on the slider will bring it down to about 9.5 dB which make a big improvement in your connection speed without seriously risking stability.
An in-between setting of 50% on the slider reduces your target noise margin by about 3 dB, which will give you maybe 400-600 kbps increase in your connection speed.
So if you want to have a play with the slider, what you really need to do is experiment with fairly small changes at a time. But don't do it too frequently (not more than once an hour, I suggest) otherwise you are cause DLM to flag your connection as unstable, and raise the target margin further.
Thanks Eric for the above.
I guess I am after line stability more than anything. Periodically I would lose sync in the early hours due to low SNR. What I hope to achieve is to try and prevent this drop of sync.
Hopefully if achieved my bras profile will become more stable, instead of fluctuating every few days.
0 6000 6816 adsl6000 Auto 06-Apr-2009 03:38 06-Apr-2009 03:38
448 7000 7968 adsl7000 Auto 03-Apr-2009 08:56 03-Apr-2009 08:56
0 5500 6240 adsl5500 Auto 03-Apr-2009 01:14 03-Apr-2009 01:14
0 7000 7968 adsl7000 Auto 02-Apr-2009 12:17 02-Apr-2009 12:17
448 7150 8128 adsl7150 Auto 29-Mar-2009 00:15 29-Mar-2009 00:15
0 6000 6816 adsl6000 Auto 22-Mar-2009 00:16 22-Mar-2009 00:16
448 7000 7968 adsl7000 Auto 16-Mar-2009 00:15 16-Mar-2009 00:15
0 6000 6816 adsl6000 Auto 12-Mar-2009 05:08 12-Mar-2009 05:08
448 6500 7392 adsl6500 Auto 06-Mar-2009 10:09 06-Mar-2009 10:09
0 5500 6240 adsl5500 Auto 28-Feb-2009 23:56 28-Feb-2009 23:56
Downstream RX
Noise Margin: 6.9 dB
Connection Rate: 7680 Kbps
Line Attenuation: 28.0 dB
Power: 19.8 dBm
Max Rate: 8416 Kbps
SF: 74634
SF Errors: 1
Reed Solomon: 10150288
RS Corrected: 879
RS Un-Corrected: 25
HEC: 1
Errored Seconds: 186
Severe ES: 1
Interleave Depth: 64
Upstream TX
Noise Margin: 21.0 dB
Connection Rate: 448 Kbps
Line Attenuation: 15.5 dB
Power: 12.0 dBm
Max Rate: 1112 Kbps
SF: 75813
SF Errors: 0
Reed Solomon: 644410
RS Corrected: 0
RS Un-Corrected: 0
HEC: 0
Errored Seconds: 0
Severe ES: 0
Interleave Depth: 4
Totals
Total Up Time (As Reported):
1 days 41 min 0 sec
CRC: 387
LOS: 0
LOF: 0
ES : 186
Bytes Transferred (ppp0):
Tx: 68378802 (65.2 MiB)
Rx: 688845447 (656.9 MiB)
IP address: 82.69.119.122
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Hi
It is a mystery how the SNR margin changes . these are some of my stats
Noise Margin: 6.3 dB lowest 5.9 highest 9.1
this varies in steps of 1 to 2 db as if something/s is coming on or off no fixed times
Connection Rate: 6912 Kbps
Line Attenuation: 33.0 dB
Power: 19.8 dBm
Max Rate: 7712 Kbps
Total Up Times (From SF counts):
WAN: 12 days, 02:03:09
LAN: 12 days, 02:03:43
CRC: 58
LOS: 0
LOF: 0
ES : 45
And before this I had a 4week run with similar error rates rates. I rebooted to see if the marging had dropped .It hadn't . My target is still 12 db.I have tweaked it down to 9db using Routerstats .So altogether its been over 6weeks since the last Target change from 15 to 12 . :(
regards Jeff
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I have a loose theory on the automatic reduction of the target SNRM (or should I say a loose understanding of it? :P )
So, here goes:
it seems that the 14 days intervals will work as has already been reported by roseway and a lower SNRM will arrive including a resync at a higher connection speed, but this is affected by the current service option setting at the local exchange, of 'normal', 'stable', 'super stable'.
I believe that the counts of FECs, CRCs, or errored seconds, etc. are not absolute, but relative to the service option that the line has assigned to it. So, with the same error counts you could have a higher sync speed (and achieve an automatic resync to a lower SNRM) if your service option is 1, but won't if your service option is 3. Now if you live next to the BT exchange a setting of 3 will not affect your speeds, but on a longer line you'll probably be on a loser and will soon be bounced to a high noise margin with no chance of achieving an automatic reduction (because your error counts will be deemed unacceptably high on a service option of 'super stable').
I moved ISPs and the new ISP mentioned somewhere in their literature that all new connections are as a default set to 'super stable' for maximum line stability. I didn't pay attention to this, but within a week or two from moving I started having resync events and in no time at all ended up with an unshakeable 15dB SNRM. Even when I asked the new ISP to manually reduce the target SNRM from 15 to 9dB, within a couple of days the DLM jumped up to 15dB in a single step. I am assuming that my previous ISP had reset my connection to normal after I asked them to reset my target noise margin to default 6dB, because I used to have 6dB SNRM and 7616 kbps sync speeds for months and months on end, until I joined the new ISP.
I have now asked my new ISP to change the service option from super stable to stable - will report back how it goes.
Using routerstats or modem commands to force the SNRM lower than what the DLM is offering is essentially working against the logic of the system. If my theory is correct then it may be a better solution to reset the service option to 2 or 1 via the ISP support desk - unless the line is soooo noisy that it will soon end up dropping the connection. If the latter is true then the line will have drop outs with routerstats anyway and a 'stable' or 'super stable' choice may be necessary to make the connection usable.
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That's an interesting theory, Mick. When I first heard about these service levels (from ADSL24) it was suggested that they directly related to target noise margins, but your theory sounds very plausible. If, as has been suggested, customers will in future be personally able to set the service level on their account, then allowing them to tweak the behaviour of the automatic DLM process, rather than to override it absolutely, would make a lot of sense.
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>> 'super stable'
That kinda rings a bell with the 21CN DLM system which is supposed to be slightly different. I'd need to dig out the stuff I have somewhere, but iirc it was mentioned that these profiles may also apply at some point to WBC.
The long term plan is for users to be able to select and change their own profiles much easier.
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I like Mick's theory.
In my case, I had a steady 9dB margin for several years then, owing (stupidly) to an afternoon spent experimenting with different filters and things, I managed too many resyncs and earned my 15dB target margin. I eventually persuaded demon to get it brought down to 9dB again, but 2 days later it was back at 15dB and it's stayed there ever since (6-7 months ago).
Now, suppose that for some reason that my service option also got changed as a result of that initial sequence of events, either by some misunderstanding by demon, or by some policy within BTw, or whatever, it would explain things nicely...
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Hi
At long last my SNR target has dropped again is now 9db.This happened without me rebooting or anything . I did not lose pppoe or any connection WAN or Lan . Its taken about 7 weeks to drop from 12 to 9 . Had quite a bad storm about 10 days ago where errors climbed for a couple hours . Maybe that delayed the change ?? my router has been up continuously for 20 days .
Regards jeff
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Thanks for your observations guys.
Interesting another report that there was no resync or loss of PPP session.
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If I May ask
Is it beneficial to use the DGTeam firm ware to artificially lower your SNRM against the DLM process? I guess what I am asking is, Is it better to leave artificially lowering of the SNRM alone and just hope and pray the DLM will see the line stable and over time lower the SNRM automatically?
Will using the DGTeam firmware to lower SNRM hinder the DLM process.
Sorry if I'm making a hash of this but its the only way I can convay what I wish to ask.
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If you want DLM to have the best opportunity to reduce your target noise margin automatically, then you should leave it untweaked. If you tweak the target noise margin down, then you are likely to increase the error rate, which can increase the time taken to get the reduction, or stop it happening altogether.
That being said, in my case I did tweak the margin down a bit, but I kept a close watch on the error rate, which was very low. Every case is different of course, so it's hard to make general rules.
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I promised to report back and here I am! :)
I can confirm that after my ISP asked BT to change my Service Option to 'stable' (from 'super stable') I have for more than a week been holding onto a SNRM of 9dB (previously was nailed at 15dB come what may) and a BRAS of ADSL 6000. :thumbs:
I have seen some degradation of the sync speed over the week (from 7028 to 6816 kbps) but this could be due to weather conditions and whatever else. I have recorded a clear increase in average and maximum FECs/CRCs compared to when I was running at 'super stable' setting, but these errors do not seem to have affected my ability to hold onto 9dB! Furthermore, last Friday we had three power cuts (two of them in really quick succession) and this did not affect DLM's view of my line either. This was despite the fact that one resync event was below 6815 kbps, which simply resulted in a ADSL 5500 for now. Under my previous 'super stable' setting any event like this would have forever kicked my SNRM up to 15dB.
I am curious now to see if I may go through an auto-reduction in SRNM after a fortnight (power cuts allowing). Watch this space!
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That's interesting Mick. When your service option was changed from super stable to stable, did your target noise margin immediately reduce to 9 dB?
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I didn't want to complicate matters so I omitted this part. The ISP asked BT to lower the SNRM to 9dB.
The bummer is that BT also changed my FTR to 3200Kb/s (MSR=4000Kb/s), when they previously were FTR=4992Kb/s MSR=6240Kb/s. I queried this with my ISP. On the 20CN this would be the result of line (re)training. However, I am told that on the 21CN, changing the Service Option causes a retrain. This means that unless the sync speed drops below 3200 kb/s the BT boys are not coming out to check for faults. :(
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Mick...
FYI, I think There is another rumoured relationship between FTR and target margin, and I'd be interested to know if you feel that part of your recent experiences can confirm or deny it...
...according to one of the BT patent papers, DLM won't increase the margin if it would reduce your speed to less than FTR. Further, it assumes a speed drop of 800kbps for each increment, so it won't increment unless you're already syncing at 800 above FTR.
Even if it's true, I don't think it affects your current circumstances as your line as DLM was able to apply a 15dB margin even at your earlier fault rate. So the worst scenario that could happen is your margin could increase to 15 again, just as it did before.
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...according to one of the BT patent papers, DLM won't increase the margin if it would reduce your speed to less than FTR.
Well, in my case it increased from 9 to 15dB and this reduced my sync speed to just below my FTR. My ISP said that if we were to call out BT to investigate luck would have it that their modem would sync just above my FTR and they would register a no fault found.
Further, it assumes a speed drop of 800kbps for each increment, so it won't increment unless you're already syncing at 800 above FTR.
I wish it were like this, I would have stayed at a 9 or even 12dB SNRM, but as I said it increased straight up to 15dB. This happened more than once on the occasions that I asked my ISP to reduce the SNRM to 9dB.
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Thanks Mick.
It's interesting, if disappointing, to know that patent doesn't exactly descibe DLM.
However, the bit about going straight from 9dB to 15dB is consistent with the BT patent, whereby a line that is 'very poor' will move two steps towards 'stability'. It also reflects my own experience shortly after getting an ISP-requested reduction. If the definition of 'very poor' varies with service option, it's all consitent with your theory.
Speculating further... whatever 'flow chart' the off-shore ISP call centres use for dealing with customers requesting anything that involves BT, the first step could easily be to 'move to a more stable service option', before even bothering to talk to BT. But that would be entirely the wrong thing to do if the request is for a target SNMR reduction....
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It's interesting, if disappointing, to know that patent doesn't exactly descibe DLM.
I think that my experience alone is not enough to deduce a pattern on this matter. It may well be that the patent works in this way, but it is allowed to go only just below the FTR value (by how much?) My sync speed was below FTR but only just (like 50-80 kbps with a Netgear router from what I recall). As the long days arrived in Spring I was soon able to sync at higher than FTR speeds using a different router.
Speculating further... whatever 'flow chart' the off-shore ISP call centres use for dealing with customers requesting anything that involves BT, the first step could easily be to 'move to a more stable service option', before even bothering to talk to BT.
Aha! But the ISPs have to talk to BT to effect a change in the Service Option setting. As I understand it this is all performed at the exchange equipment. Have a look my attached ticket log to see if it makes sense - BT mention that a lower sync speed will not go below the FTR! ;)
[attachment deleted by admin]
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I think that my experience alone is not enough to deduce a pattern on this matter. It may well be that the patent works in this way, but it is allowed to go only just below the FTR value (by how much?) My sync speed was below FTR but only just (like 50-80 kbps with a Netgear router from what I recall). As the long days arrived in Spring I was soon able to sync at higher than FTR speeds using a different router.
The way the patent describes it, the decision to raise the margin is taken based on a prediction of your resultant speed, rather than an actual measurement of the result. So, in the extreme, if your speed was FTR+801 then DLM could raise the margin. But of course the 800 speed variation is just an estimate, and it's quite possible it could actually drop by 802 or more. I don't see any mention in the patent of anything that would rectify such cases.
Aha! But the ISPs have to talk to BT to effect a change in the Service Option setting. As I understand it this is all performed at the exchange equipment. Have a look my attached ticket log to see if it makes sense - BT mention that a lower sync speed will not go below the FTR! ;)
I can't say I've followed or understood everything that was said in your ticket log, but I do see the bit about 'line has been remotely stabilised' but that the resultant lower line rate '...wont breach FTR'. That does seem consistent with the idea that the DLM algorithm is designed so as to not reduce speed to less than FTR.
I must say, your ticket makes fascinating reading even though I can only guess at what most it means. And I'm impressed that your ISP has (a) had the willingness and determination to see it through, and (b) been willing to be so open with you about it all.
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I have been holding my breath for the last few days now. As the days are growing longer signal strength has been improving all the time. I am still waiting in hope that the DLM will auto-reduce my 9dB SNRM to 6dB. Over the last couple of days I noticed that during day time the SNRM increases from 9dB to 10dB and during the night it does not drop as low as it used to. If I were to resync now I would probably increase my sync speed and profile. However, I am not sure if the higher SNRM that I now see will lead to an autoreduction - what shall I do? Resync, or wait?
PS. Green in the graph is the 9dB that I obtained last time I sync'ed. The blue line indicates the real time changes in SNRM.
[attachment deleted by admin]
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I think it's best to re-sync as rarely as possible during this period, because each one will be a small extra item on the debit side, so to speak. Also, if you were to re-sync at a higher speed, this would quite possibly increase your error rate, which would be another debit.
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Thanks roseway, I'll wait. I hope that the error rate will otherwise stay low and eventually SNRM will reduce to 6dB. 18 days and counting ...
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(Apologies for resurrecting this old thread, but I thought that my somewhat delayed conclusions may help others too).
So, I waited, ... and waited ... and waited ... :oldman:
and nothing happened!
Following the change of my service level from 'Super Stable' to 'Stable' my target SNR reduced down to 9 and I stayed there for ever. Then months later with no target SNR auto-reduction I gave up and contacted my ISP once more. I asked them to change my 'Stable' setting down to to 'Normal'. Well, within 14 days I received the automatic resync from the exchange and suddenly I found myself running at 6dB SNRM and sync'ing at a full 7616Kb/s, which gives me a BRAS ADSL 6500. :)
The error count has gone ballistic (see graph) at times higher than what I had previously experienced during lightning storms! However, with the new setting of 'Normal' the line seems to have been stable, not losing its sync at all. This is despite some line cross talk which significantly increases the error count during 4-5 days a week. I have been running now for more than a month and have a stable connection and the highest sync speed that my 20CN connection will support with Interleaving on.
So, having been around the houses I have concluded that the first thing to tweak for achieving and holding onto higher sync speeds is the service stability level. 'Super Stable' requires a very quiet line/strong signal, or you'll soon find yourself locked at a high SNRM and not being able to get rid of it. If you have a high attenuation you may not be able to hold onto a 'Normal' setting and a 6dB SNRM, in which case a 'Stable' setting with 9dB is the best you can hope for.
Hope this helps others and their deliberations with their ISP. :)
[attachment deleted by admin]
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Hi Mick,
If you can hear audible cross talk you should be able to report a telephone line failure to BT, not mentioning the broadband service at all.
The fact you have lots of forward error correction counts shows that the modem is working hard for you.
It's the other error types which can be more of a nuisance.
Kind regards,
Walter
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If you can hear audible cross talk ...
Thanks Walter,
I'm afraid that the cross talk is in the inaudible range. The only way I know that it is/not happening is when the offending household are on holiday, or have switched their modem off. At those times I can see my errors dropping from hundreds or thousands down to zero and consequently my sync speed and SNRM improving. These guys are costing me 1dB in terms of SNRM and a couple of hundred of kb/s sync speed, but there's nothing much I can do. When I spoke to a BT guy he said that they have no spare loops in the pipe for my area.
Anyway, with the 'Normal' option setting I can get full speed at last, which makes me a very happy camper.
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On theory I have is that, because my line is so much improved (just by cutting the bell-wire) since the 10-day period, DLM can increase the target without me getting anyware close to my FTR. And just maybe, because I'm syncing at a long way above my recorded FTR, DLM is less inclined to give back my margin.
I'd be inclined to believe that. After a line fault in May 2009, my target margin went from 6 to 12dB. Despite holding sync for long periods with low error rates, nothing happened for nearly 6 months, until I lost service due to a MUX fault in the exchange. When that was fixed, the target margin reduced to 9dB almost immediately, then to 6dB within a few hours.
Earlier this year it occurred to me that as my wiring arrangements were less than ideal on commencement of ADSLMax, my FTR would be pretty low - 2278 as it turned out, though my sync is now around 5000. I therefore asked Plusnet for an SNR reset, after which the FTR was 4096.
A few weeks ago, I had a short period of temporary and unexplained high errors, which upped the target margin to 9dB. When the errors returned to the normal low rate, the target margin went back to 6dB in about 14 days.