Cisco Cisco IOS Software Release 12.2

In rare instances during testing, a redundant NI-2 card sometimes appeared to be functional but was not. 
Issuing the redundancy reload-peer command corrected the problem every time.

The reported DMT aggregate bit rate is less than the true attainable bit rate.

Due to line condition variations between trains, the effect of trellis encoding, interleave delay, FEC 
check bytes, and so forth, the attainable bit rate estimate is not always 100 percent accurate. A 
conservative approach was taken in making the estimate; therefore, in general, you can get a higher rate 
than what the estimate suggests. For a fast-path scenario, the results should track fairly closely for the 
downstream rate and err on the conservative side for the upstream rate. For an interleave path scenario, 
the results are highly dependent on configurations.

At a higher reach or where line conditions are not optimal, trellis encoding, interleave delay, and FEC 
check bytes can provide a much higher rate than was estimated (greater than 128 kbps).

There is no workaround. The aggregate bit rate calculation is an estimate, which does not accurately 
model all of the line conditions that affect the true attainable bit rate for a given profile. The calculations 
for aggregate bit rate are performed as follows:

The downstream capacity is obtained from the number of Reed-Solomon payload bytes per frame 
exchanged during line training, that is, the K value. The per-second estimate is then calculated from 
this K value. An extrapolated margin value is derived from the per-second estimate to make sure that 
if the line is trained at the estimated rate, it has an adequate margin.

For upstream, unlike downstream, the Reed-Solomon payload bytes per frame is not readily 
available. Furthermore, unlike downstream, which requires a CPE EOC response to know the 
downstream margin, the upstream margin is readily available at the CO (upstream margin is 
measured at the CO end). Using this upstream margin and the number of bins utilized for upstream, 
an estimate of upstream attainable bit rate is made. (The associated DDTS numbers are 
CSCdv05351 and CSCdv05322.)

The CPE does not train or perform reliably when the Discrete Multitone (DMT) profile is set to use 
overhead framing mode 0, 1, or 2. 

Overhead framing modes 0, 1, and 2 are not supported at this time.

Overhead framing mode 3 is designed for use with ATM. While overhead framing mode 1, which is not 
currently supported, is designed for Synchronous Transport Module (STM) mode. Configure your profiles 
to use overhead framing mode 3. Overhead framing mode 3 uses only 32 bytes of administrative overhead. 
Compared with overhead framing mode 1, it allows more bandwidth to be allocated to user data.