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cable upstream modulation-profile
the upstream exceeds the threshold for the primary profile, the upstream switches to the secondary
modulation profile. When the noise conditions improve (defined as a SNR value that is 3 dB greater
than the threshold value and FEC counters that are below the threshold values), the upstream
automatically switches back to the primary modulation profile. If the noise conditions continue to
worsen, however, the line card begins frequency hopping to find a cleaner upstream channel.
For example, the primary modulation profile could be configured for 16-QAM (or mixed 16-QAM
and QPSK) operation, while the secondary profile could be configured for QPSK operation. If noise
conditions on the upstream threaten to force CMs offline, the upstream switches to the secondary
profile to implement QPSK operation. When the noise ingress conditions are solved, the upstream
switches back to 16-QAM operation.
Note
When Dynamic Upstream Modulation is enabled and spectrum groups are configured on the same
interface, the line cards respond to excessive noise by first switching to the secondary modulation
profile. If noise conditions worsen, the line card attempts to find a new upstream channel by
frequency hopping, and if that fails, the line card reduces the channel width.
•
The upstream port is on a Cisco uBR-MC16S line card that is used on Cisco CMTS routers using
Cisco IOS Release 12.1(7)CX1 or later release, or on a Cisco uBR-MC5X20S/U line card.
The Dynamic Upstream Modulation feature on the Cisco uBR-MC16S line card is identical to that
for other line cards except that the spectrum management hardware onboard the Cisco uBR-MC16S
or Cisco uBR-MC5X20S/U line card uses the CNR instead of the SNR value. The CNR value is a
more accurate description of noise conditions on the upstream. Because of this, these line cards
switch back to the primary modulation profile when noise conditions improve to a CNR value that
is only 1 dB greater than the threshold value (assuming FEC counters are also below the threshold
values).
Note
When Dynamic Upstream Modulation is enabled and spectrum groups are configured on the same
interface, the line cards respond to excessive noise by taking the first corrective action, as
determined by the cable upstream hop-priority command (either frequency hopping or changing
to the secondary modulation profile). If noise conditions worsen, the line card takes the second
corrective action that has been defined, and if that fails, the line card takes the last corrective action.
The Dynamic Upstream Modulation feature uses the DOCSIS-specified thresholds for 16-QAM and
Note
QPSK operation to determine when to switch modulation profiles. We therefore recommend that the
primary profile use 16 -QAM or mixed 16-QAM/QPSK modulation, and that the second profile use
QPSK modulation. However, this is not mandatory, and the two profiles could be the same (16-QAM or
QPSK), but the secondary profile should still be considered a more robust profile than the primary profile
in terms of coping with noise conditions.
Cisco Broadband Cable Command Reference Guide
2-334
For more information on this form of the Dynamic Upstream Modulation feature, see the
chapter, Spectrum Management for the Cisco Cable Modem Termination System, in the
Cisco CMTS Feature Guide.
If the Cisco CMTS router is running Cisco IOS Release 12.1(3a)EC1 or a later Cisco IOS
release, the Dynamic Upstream Modulation feature on the Cisco uBR-MC16S line card
operates the same as it does on the other line cards.
Chapter 2
Cisco CMTS Configuration Commands
OL-1581-08
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