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packzap
join:2001-08-08
North Bend, OR
| reply to AthlGrond
Re: More On FEC and Interleave
So, I gather from the above discussion that Near End Fec errors are corrected by the modem. Therefore, don't worry about them as you would with uncorrected CRC errors.
Here's what my Actiontec GT 701 (with 5.5 firmware) shows for those errors (down/up, I guess):
Near End RS FEC (105264/0)
Far End RS FEC (312/0)
I've noticed the Near End Fec errors increase quite a bit according to the DSL speed you have with Qwest. Previously, when I was at the lower 256 kbps tier, the
near End Fec's were much lower, over time, than I now get at 1536 kbps.
I don't know how you can be assured a Cisco 678 modem will result in better permormance? | |
AthlGrond
Premium,MVM
join:2002-04-25
Aurora, CO
 ·Comcast
| said by packzap  :
I've noticed the Near End Fec errors increase quite a bit according to the DSL speed you have with Qwest. Previously, when I was at the lower 256 kbps tier, the near End Fec's were much lower, over time, than I now get at 1536 kbps.
This makes sense from the standpoint of how DMT works. The more bandwidth you use the more of the frequency space will need to be used, so less reliable (for your line) frequencies will need to be used. At lower speeds the more noisy frequencies will be avoided.
(As swiped from CommsDesign again)
DMT
Dividing the available bandwidth into a set of independent, orthogonal subchannels is the key to DMT performance. By measuring the SNR of each subchannel and then assigning a number of bits based on its quality, DMT transmits data on subcarriers with good SNRs and avoids regions of the frequency spectrum that are too noisy or severely attenuated. The underlying modulation technique is based on quadrature amplitude modulation (QAM). Each subchannel is 4.3125 kHz wide and is capable of carrying up to 15 bits.
said by packzap :
I don't know how you can be assured a Cisco 678 modem will result in better permormance?
I don't know how you could be assured of that either. 
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