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. 289
Accept default upstream power level. Default
= 0.
Power range varies with channel width
selection.
Range = -10 to 26 dBmV if channel width is
3.2 MHz
configure interface cable-upstream <slot/port> cable power-
level 0
Measuring SNR in the 12U/24U CAM
For the upstream channel Signal-to-Noise Ratio (SNR) in the C4 CMTS, there are two types of SNR: Channel SNR and
Modem SNR. Channel SNR is calculated on a upstream channel basis and the per Modem SNR is calculated from the
primary upstream service flow (primary SID) of the modem. TDMA and SCDMA Long Term Slicer Error Power is also used
for calculation of the logical channel SNR. If the current Channel SNR is 0 (no traffic on the upstream), the SNR algorithm
uses Long Term SNR calculation based from PHY Slicer error which is based upon all IUCs including contention IUCs (i.e. 1
and 3).
Two pieces of information are used in calculating SNR: symbol errors and burst counts. The SNR calculation is performed
once the burst count is greater than a certain threshold. The threshold varies depending on whether it occurs in the initial
ranging period or during data traffic. The SNR reading is 0.0dB when:
The logical upstream channel is not in service (IS state) or
No modem is registered on the upstream channel
Channel SNR Calculations
In normal operations, SNR readings reflect upstream channel conditions. The SNR readings will decrease as noise level goes
up. In an ideal condition, when noise is not present or very low, the SNR value in decibels is in the high 30’s.
Two SNR calculations are performed in the CAM for Channel SNR. SNR based from MAC (IUC4 plus all data IUCs) does not
include contention Interval Usage Codes (IUCs) such as 1 and 3. The second SNR calculation is based on all IUCs including
To Next Page
Loading...
