Примечания к выпуску для Cisco Cisco IOS Software Release 12.2(10)
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Limitations and Restrictions
OL-2702-01
Limitations and Restrictions
Limitations and Restrictions
This section describes the limitations and restrictions for Cisco IOS DSLAM releases.
Attainable Bit Rate Is Conservative on 4xflexi-DMT and 8xDMT
The reported DMT aggregate bit rate is less than the true attainable bit rate.
Limitations
Due to line condition variations between trains, the effect of trellis coding, 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.
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, the effect of having trellis coding, interleave
delay, and FEC check bytes can provide a much higher rate than was estimated (greater than 128 kbps).
delay, and FEC check bytes can provide a much higher rate than was estimated (greater than 128 kbps).
Workaround
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:
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 will still have an adequate margin.
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 will still have 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
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
Step 13
rommon> sync
Sync to save the state of rommon.
Step 14
rommon> b
When the NI-2 boots, it uses
ni2-dboot-mz.121-5da.bin as the bootstrap image.
ni2-dboot-mz.121-5da.bin as the bootstrap image.
Step 15
DSLAM# configure terminal
Enter global configuration mode. You have entered
global configuration mode when the prompt changes to
global configuration mode when the prompt changes to
DSLAM(config)#
.
Step 16
DSLAM(config)# config-register value
Set the config-register to the value you recorded in
Step 5.
Step 5.
Step 17
DSLAM(config)# exit
Return to enable mode.
Go to the
Command
Purpose