Cable Modem Cannot Successfully Range - Juniper G10 CMTS Hardware Manual

Cable Modem Cannot Successfully Range

If a cable modem cannot successfully range, the cause might be one or more of the following:
High IM, SM, and FAdj values in the flap list can be an indication of HFC plant issues that
affect ranging (see Table 45 on page 143).
The local event log might contain events that explain why a cable modem has been
deranged. Issue the show log cable command to see the local event log.
Issue the show cable modem ranging-statistics command to view ranging statistics that
might provide insight into ranging issues.
! There is too much attenuation in the return path. If the power level of the cable
modem's signal measured at the CMTS is not within the tolerable limits of the CMTS due
to excessive attenuation, the CMTS responds with an abort ranging status in the ranging
response (RNG-RSP) message to the cable modem.
You can configure the power level below the commanded power level at which a cable
modem is considered successfully ranged by including the minimum-power-level
statement at the [edit services cable upstream] or [edit interfaces
cu-virtual-slot/docsis-slot/upstream-interface cable-options upstream] hierarchy levels.
The default is –3 dB below the commanded power level. Consider lowering this
threshold to see if a cable modem can operate successfully at a lower power level.
See the JUNOSg Software Configuration Guide: Interfaces,
Cable, Policy, and Routing and Routing Protocol for
important information about changing the minimum
power level. Setting the value too low can lead to improper
CMTS behavior.
! RF plant issues in the downstream prevent the cable modem from receiving unicast
upstream bandwidth allocation MAP messages that define periodic ranging
opportunities (station maintenance) for the cable modem. In this case, the cable modem
will time out and reinitialize its MAC, causing it to drop offline.
! RF plant issues in the return path prevent the CMTS from receiving ranging request
(RNG-REQ) messages, in which case the CMTS will not provide ranging response
(RNG-RSP) messages. In this case, the cable modem will time out and reinitialize its
MAC, causing it to drop offline.
! Significant frequency error is being introduced by the frequency stacking multiplexer
(sometimes called block upconversion) in the return path.
! Frequency stability within the cable modem is degraded.
HFC Plant Related Issues
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Troubleshooting 157