Broadband Related > ADSL Issues

21CN DLM/Banding Question

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aesmith:
Hi,

Some quick questions on 21CN DLM and banding in particular.   Does anyone know (1) what's the highest noise margin that 21CN will apply in response to line error?  (2) does DLM apply banding in response to errors, or only in response to excessive disconnections.   And finally, can the ISP over-ride either target noise margin and/or banding?

Thanks, Tony S

ejs:
The highest target SNRM is 15 dB.

I don't know, and I'm not sure if anyone (publicly) knows, if the DLM takes different actions in response to errors and in response to retrains. The banded profiles do have higher than usual INP values available.

The ISP can easily set / reset the target SNRM and rate band.

aesmith:
Thanks, and if the ISP sets the band and/or target SRNM, do the stay set?

Reason for asking is that for the last year we've been reliant on using the router config to over-ride BT DLM to maintain the proper speed.  A&A had said that they can't fix SNR target on 20CN as we were then, but they'd have more control on 21CN.  We've just been moved onto 21CN, still in the 10 day training period.  A&A now a little vague about what can be done, I can see error messages back from BT in response to their attempt to set band and SNR, but that maybe because it's within that 10 day period.

Meanwhile performance on 21CN is absolute crap.

20CN was typically just over 4 meg, for example
   "Down Sync=4224kb/s LoopLoss=55dB SNR=5dB"

On 21CN it just seems worse in all parameters for example ..
  ADSL2+  "Down Sync=3068kb/s LoopLoss=57dB SNR=4.4dB"   
  ADSL 2   "Down Sync=3068kb/s LoopLoss=53dB SNR=3.9dB"

Just getting a bit concerned that we've been sold a pup and far from improving things, 21CN is a big step backwards.  Should I go a step further and disable ADSL 2 as well, effectively reverting to 20CN type modulation?

kitzuser87430:
Hmm. I am waiting for a 21CN "upgrade" as well.

Do you know if you were interleave/fastpath on g.dmt;

 have you any quiet line/hlog graphs from before the upgrade....

Just found you on MDWS your bits/tone shows where you are losing speed.

What modem are you using and what exchange equipment has been installed.

I have an nagging thought about an unsolved  line problem on your rural line, by your error seconds pre and post move to 21CN.

Ian

aesmith:
Cheers.  It's a Billion 7800DXL, I don't what type of kit is in the exchange.   Errors come from an electric fence which affects (according to BT) all users on the 50 pair cable with no solution available.   On 20CN we dealt with the situation by over-riding target SNRM on the router and there was an obvious relationship with lower SRNM giving higher synch speed, higher SNRM with lower synch.  What we have now is the sort of speed that 20CN would reach at 12dB SNRM, but even at that low speed the stats are showing what looks like an unhealthily low margin.

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