A possible datapoint on DLM

Two weeks ago a BT engineer tested my line. It was part of an ongoing problem I have and, frankly, neither myself nor my ISP wanted a line test but that's what I got. The only consequence was that I ended up with interleaving (1041) on my line and my speed dropped from 73Mb/s to 66Mb/s. It looks like the interleaving has been lifted - exactly 14 days later this morning at 5am. So that's something to think about perhaps for those trying to work out how the FTTC DLM works.

As for my ongoing problem that's on hold until the 21st of April. I think the fault lies within BT Wholesale's network but it's proving difficult to get them to accept/understand that. It seems to me that they just pass any faults on to BTor or reject them back to the ISP.

That's a bit odd. I got home and checked my modem and now that interleaving has been reduced the attainable rate has dropped from 78Mb/s to 71Mb/s. Does that seem reasonable?

Prior to the engineer visit attainable was 76Mb/s and the modem would sync at 73Mb/s.

I think so, same happens to me when interleaving is off (which isn't very often, but it is at the moment as my connection was reset by OR a few days ago). ATM my attainable and actual are virtually identical and, on occasion, actual has been higher than attainable.

I recently read somewhere (unofficial) that BTOR have started resetting DSLAMS to deliver stability rather than speed (possibly due to increased take-up increasing 'noise interference' / crosstalk), thus resulting in lower attainable rates.

My own connection's DS SNRM dropped suddenly by 3dB or so 31st December & for a few days my sync speed remained the same.

Eventually it resynced back at the usual 6dB SNRM, but sync speeds reduced by almost 4Mb.
DS Attainable rate has also reduced by around 2Mb or so when SNRM is at 6dB.

My DS sync speed is now down to around 25.72Mb, whereas it had remained at just below 30Mb for many months prior to 31st December

My connection is very steady, but attainable rate & sync speed show no signs of improvement, so there MAY just be some truth in what I read.

Edited by deleted (Mon 11-Mar-13 20:06:31)

Had a fault on my FTTC line a month or so ago and it has taken 5 weeks to get back to something akin to normal. Before the fault, I was getting max attainable rates of 100/32, SNR 10, INP 0. Synch dropped to 37/1.1 and achieved 80/20 synch about 3 weeks later. Max attainable at 80/20 was 85/28 with a downstream INP of 3, SNR 7 and FECs of 320K/hour. The downstream FEC rate dropped to 80k/hour, 20k/hour and then 5k/hour over a period of 2weeks. Yesterday AM router re-synched at 93/27 (still on a 80/20 profile), INP 0, SNR 10 with 60 downstream FECs/hour. I am sure that it is just the DLM doing its thing but it takes a lot longer than most people think. Probably explains why users on long copper links don't immediately regain the synch that they had previously.

yes is expected.

On adsl my sync speed was always higher when interleaved, and when I got interleaved reently on vdsl (I made a post), my attainable went up although the actual sync was lower due to FEC but the attainable was higher.

Not quite sure why, whether the dslam bumps power or the delay gets a higher sync I dont know but its something I have noticed consistently on xDSL.