Due to attenuation/distance from the cabinet, my connection is unable to make use of the higher frequency tone band plans & you will see high bit-loading in the lower band plan.
Having seen quite a few connection stats now,
While trying to make sense of the bit-loading issues I saw, I started trying to work out how much data needed to be sent by the modem for FEC to work. Obviously FEC (as part of interleaving) only works by sending extra parity bits - and DLM is in charge of the configuration of this - butthose parity bits must be sent "invisibly" to the Sync speed, but "visibly" to the bit-loading graphs.
By that I mean that the parity data must be sent in buckets that are viable for carrying data, but an increase in parity size does not increase the sync size.
As a conclusion, the space used by FEC can therefore decrease your sync speed, if the "capability" of the line is close to the caps.
According to an article on FEC
, the parameters N and R are important: N being the number of bytes in a codeword, and R being the number of parity bytes in that codeword - therefore (N-R) bytes are real user data.
The important bit that the (N-R) bytes go within the sync speed, and the R bytes go on top.
In one of your old posts where speed was 27Mbps, N was 44 and R was 12. For every 32 bytes of data you sent (inside the 27Mbps), another 12 bytes of parity data was being sent outside it - or about 37%. On a perfect line without interleaving, that would be another 10Mbps.
In the data kept within the graphing scripts, some more recent stats showed a speed of 28Mbps, N of 80 and R of 16. For every 64 bytes of data, 16 bytes of parity data ae being sent - or about 25%. That would be another 7Mbps.
So it could be that you are suffering a double-edged blow from noise. The noise level is lowering SNR, which means you get less Bits to play with; and then a good proportion of those bits are being stolen to carry FEC parity data. But again, we don't have the "before" figures to tell quite so easily.
I wonder if I am reading the N and R values correctly from the stats...