Kitz yeah but have you seen any other modems over estimate by such a large number? to have that estimate on a 6db margin is completely whacked.
Nope. In theory the maximum bit loading on a line that is perfect is somewhere just a little over 3Mbps per 1dB of SNRm or 3.8 Mbps if there were no PSD masks.. and Ive no idea how much effect PCB will have.
Also remember the router reports an average figure for the SNRm so there may be some tail end tones which couldnt load any more bits into the bin even if there was a 1dB rise. (It needs 3dB over base line to load one bit).
So basically take attainable with a pinch of salt when interleaved.
Unfortunately yes. The modems dont seem to adjust correctly to RS overheads.
Could the high attainable rate be the cause of the unusually high FEC count when interleaved?
Not the FECs - unlikely.
The attainable rate is mis-calculated somehow, my theory is that it might be calculating the attainable rate of what it would be at around 0 dB SNRM.
More likely no proper adjustment for error correction overheads and its somehow adding the RS Correction redundancy on to the throughput figure. In cases like this then you'd expect the max attainable to increase each time a greater depth of Interleaving & Err/Corr is applied by the DLM.
Another area is that it may not be adjusting properly to PCB or PSDmasks and performing the calculation without due consideration that those particular tones wont attain any higher sync speed regardless if there is more SNRm. Bearing in mind that PSD masks can easily knock 2 or 3 bits per bin out.. that could amount to quite a bit of sync speed.