Chapter 9: Upstream Cable Access Modules (UCAMs)
STANDARD Revision 1.0 C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved. 290
IUC1 and IUC3. The two SNR values can be obtained with show cable noise cable-upstream slot/uport detail CLI
command. The show cable noise CLI command outputs only the SNR without the contention IUCs.
The channel SNR calculation is the same between the 12U and 24U CAM. The SNR is based on the MAC (IUC4 + all data
IUCs) excluding contention IUC1 and IUC3. A burst count threshold of 100 packets is used in the calculation and the MIB
attribute for this SNR is docsIfSigQSignalNoise. The show cable noise
CLI command outputs this SNR whereas the show
cable noise cable upstream slot/uport detail
CLI command outputs additional SNR calculations based from the PHY
chips where the SNR calculation includes all IUCs including contention IUCs.
Besides the SNR measurement, the CMTS uses FEC counters to provide additional information to describe the condition of
an upstream channel.
The CLI command show cable noise outputs the SNR from IUC4 + all data IUCs and FEC counts as shown below:
Upstream Cable
Port Mac SNR(dB) MicroReflection FEC_Unerrored FEC_Corrected FEC_Uncorrected Codewords In Error(%)
--------------------------------------------------------------------------------------------------------------
3/0 1 38.6 0 4229 0 0 0.00e+00
3/1 1 38.5 0 3000 0 0 0.00e+00
3/12 1 44.2 0 7757 0 0 0.00e+00
3/13 1 41.6 0 8537 0 0 0.00e+00
Note: The MicroReflection column is shown in the table, but is not supported in any release. As SNR values decreases, the
probability of FEC Corrected and FEC Uncorrected increases.
CLI commands show cable noise cable-upstream slot/port detail shows both calculated SNR values. For 12U CAM,
Channel SNR is output as shown below:
show cable noise cable-upstream 3/0 detail
CAM/US: 3/0 Cable-Mac: 1
SNR from MAC BCM3214, IUC4 + all data IUCs : 37.9
SNR from PHY BCM3140, TDMA all IUCs : 37.7
For 24U CAM, Channel SNR is output as shown below:
show cable noise cable-upstream 3/0 detail
CAM/US: 3/0 Cable-Mac: 2
SNR from BCM3142, IUC4 + all data IUCs : 38.7
SNR from BCM3142, TDMA all IUCs : 37.9
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