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Interleaving turned on - any reason?

grahamt
Rising Star
Posts: 567
Thanks: 13
Registered: ‎05-04-2008

Interleaving turned on - any reason?

After having had a nice, solid connection with more than four days uptime and an SNR that never dipped below 6, BT's DLM (I presume) decided to resync my line this morning at around 10am (when my SNR was 12). I've no idea why. I've also no idea why interleaving was turned on during this resync - or indeed why it was turned off beforehand.
My downstream speed is banded, so I'm syncing at the same rate as before, 6653. Upstream has moved from 816 to 805 (after having been at 816 for several weeks). Maybe the upstream speed change is related to interleaving?
Could anyone hazard a guess at why the interleaving should be changed? I don't mind it - I'm just curious.
Graham
3 REPLIES
Superuser
Superuser
Posts: 6,810
Thanks: 878
Fixes: 56
Registered: ‎30-07-2007

Re: Interleaving turned on - any reason?

I was looking at a presentation on the workings of the 21CN DLM not long ago and it seems like the first thing it does to stabilise a line is to apply interleaving, then it starts to up the taget noise margin only if that doesnt work.
grahamt
Rising Star
Posts: 567
Thanks: 13
Registered: ‎05-04-2008

Re: Interleaving turned on - any reason?

Thanks. I'm not sure my line is any more stable now, though. After four days uptime on fastpath I'd got around 9500 near-end FEC errors. After just an hour on interleaved I'm already up to 23000. Could be ominous...
Maybe I should specify interleaving to be turned off when the new DLM trial starts.
Graham
Superuser
Superuser
Posts: 6,810
Thanks: 878
Fixes: 56
Registered: ‎30-07-2007

Re: Interleaving turned on - any reason?

FEC errors shouldnt be a problem since they are 'corrected' errors, its the HEC ( and maybe CRC ) errors that the DLM is interested in I think.