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Message 1 of 2

Early morning restarts by DLM

I've read a few posts recently about restarts by the dslam, normally early morning.


Here's my take on it ... notwithstanding I've had and resolved (hopefully) problems of my own.


With ADSL2 and 2plus connections dynamic line management works on the fly, and under normal healthy circumstances set the profile linespeed with default 6db noise margin ... but because it works on the fly and on both data paths independantly if it sees interference of an electrical impulse nature it will adjust noise margin accordingly and can react almost instantly if and when the MSAN pulses the line connection (which happens regularly throughout the 24 hour period) but more of that later.


It will by default increase interleave first because that doesn't decrease linespeed, but SNR increase does decrease linespeed which goes against BT's policy of supplying the end user with the fastest connection possible. It's normally huge burst noise or for example line crackle that will enforce the modem to drop the connection with the dslam, as multiple data bucket frequencies are blinded by corruption.


With fibre to the cabinet, it's different. FTTC Msan's collect line information only once per 24 hours, but it's recorded at 15 minute intervals and stored in a history profile, which is appended every 24 hours.

Using the history of the connection as against the initial training information, the differences in the line characteristic can be compared algorithmically.

Infinity sets dslam 6db as well, apart from the still relatively small percentage of Huawei dslams trialled and set to 3db, and those connections are deemed "green flag" on performance bands.


The reason I mentioned both products is this ...  if your connection has a problem with any of the products it goes onto a virtual register of connections that are troublesome (to varying degrees) and the Msan will pulse the line after all the data collection has appended and been acted upon by DLM which in the case of Infinity uses the appended history database. As I said previously ADSL2 works on the fly but is still pulsed with all the other connections including FTTC and it happens early morning, my own was pulsed and reset around 06:00 when my problems arose. The muxes are backward compatible with both but serve to do the same action all together.


If your connection is getting worse DLM will further drop linespeed but also set timers against which improvement, or the opposite, can be gauged logically.

As the pulses increase DLM will be changing the line profile, setting differing levels of interleave and margin ... in effect giving the line more attention, and often dropping the connection.

With both products connections are banded in colours green, orange, red and so on and catergorised to give an element of control action by DLM ... again in effect, attention. (this is logic remember, not human interface)


ADSL2 was fairly forgiving ... a bad SNR, high interleave etc can be overcome in 7-10 days, often less if healing is quick even without a reset by BT.

Infinity is not very forgiving, reason being the linespeeds are far greater, corruption levels can be higher with bad data finding its way to the backhaul.

Even the smallest appended fault on a FTTC connection can reset the timer on banding resolution and you can wait weeks for an improvement ... and those improvements can come back in a gingerly fashion.

One of the main reasons BT are imposing and using g.inp on fibre dslams, to alleviate problems with error correction at the physical layer ... notwithstanding the fact that the technology itself and frequencies used have caused their own set of problems with crosstalk.


So if your connection keeps restarting early morning in both cases, you'll know why ... but leastways those restarts are not necessarily always bad news because if your connection is improving they will still happen regardless but the attention span by DLM will decrease as your connection is once again promoted from its coloured band towards getting back its MSR, until eventually they won't happen. (unless of course you still have a fault).


Hope this helps a little.



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Message 2 of 2

Re: Early morning restarts by DLM

You're almost right. One exaple MSAN on FTTC????


DLM operates at DSLAM level on FTTC.


That said the rest was mostly right.

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