I started to type something in another thread in response to a question for setecio and realised I'd perhaps gone a bit too deep into the theories bit - therefore I'll keep the factual stuff in that post... and put all the theory stuff in here since quite a bit of it relates to examples on my own line.---------------------------
Theres no explanation why stuck bRAS profiles occur - but something that I noticed fairly early on and I was possibly one of the first to suggest this is that it seems far more likely to occur on good lines.
I have an unproven theory that good lines with lots of spare SNRM dont push the DLM.... perhaps something to do with the DLM never seeing that line hitting its target SNR. (eg the type of line will always sync with a SNRM more than the target SNR). Its almost as if the DLM only acknowledges these lines when the SNRM <= the Target SNR.
2Mb is the most common reason for a line to get stuck at since if the DLM cant pick up a profile then the default profile is 2000. Hence why it can happen after a change in product.
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Now back to the why a line that is 6Mb etc why that doesnt get stuck as often.... which also lends more evidence to my theory above In that instance when the line goes back up - it will reach a point where the SNRM = Target SNR. The system at this point says "
Stop!!!! - Maximum sync achieved for the Target SNR" and then it records that event for the IP profile.
However if you have a very good line (take mine for example)... it syncs up straight off at 8128. It then may have a surplus SNRM of 14dB and therefore is way over and above the Target SNR of 6dB.. the DLM doesnt have to work or doesn't have to do anything much. Theres no negotiating of the maximum speed of what the line can handle because the line can cope with it - and could do way more if 8128 wasnt a restriction of adsl1. Theres nothing that goes "Stop" - only the limitation of adsl1.
I have problems with stuck profiles - this line would normally consistently sync at 8128 always with plenty of SNRM. But what is a real PITA as soon as I have a low sync event I get capped. Experience has shown that it can only take one single event too - god knows why Adaptive Max Logic doesn't
appear to work on it either. Its almost as if one bad sync and the DLM goes "
ooooh look STOP!!! Max sync achieved for Target SNR - hahahah found you" and then BAM I get hit. Then I can attempt another resync immediately after at 8128 and then the DLM goes "
Nah you havent hit your Target SNR - lalala cant see you - not going to record it".
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On my own line this is certainly the experiences Ive had so far
- When I was 1st maxed (stuck at 2000 despite immediate sync of 8128)
- Misconfiguration set my MaxPremium account to Max and back again. (stuck at 2000 despite constant sync of 8128)
- Move to another DSLAM shortly after BTw installed new MSANs in this exchange - (stuck at 2000 despite constant sync of 8128)
- Having a new kitchen fitted - lots of heavy duty power tools etc (stuck at 4500 after a bad sync - reboot back up at 8128)
- Having some electrical work done in the house and the electrician was flicking the main fuse box on and off without me first having powered down the router (stuck at 6000 - router came straight back up at 8128).
- Powercut and power surge on the estate. (stuck at 500 - bad sync of 736 and a period of not being able to sync followed by a reboot back up to 8128)
........... and finally where I am right now - stuck at 6500.
BT attempting to clear the stuck 500 and rather than doing a reset - did something stupid in their system which gave me a false sync event of 7392Kbps. This wasnt a true sync and why nothing ever showed in my router logs.
In still fighting this one... and I have a bit more info which I will possibly disclose when Im more certain... but after discussion with Saffy and my ISP we have a good idea what they have done. If so - it wasnt perhaps the best thing to do on a line that has a record for getting stuck :mad:
