Cable Modem Cannot Successfully Range

HFC Plant Related Issues

If a cable modem cannot successfully range, the cause might be one or more of the following:

!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-levelstatement at the [edit services cable upstream] or [edit interfaces cu-virtual-slot/docsis-slot/upstream-interfacecable-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.

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-statisticscommand to view ranging statistics that might provide insight into ranging issues.

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Troubleshooting 157

Juniper Networks G10 CMTS manual Cable Modem Cannot Successfully Range

Models: G10 CMTS

HFC Plant Related Issues

Cable Modem Cannot Successfully Range