Troubleshooting guide

Troubleshooting the CMTS
4-67
4. Inspect amplifiers if there is an attenuation problem on the downstream path.
View CMs that proceed or follow an amplifier in the downstream path to
isolate the defective amplifier and replace or repair it. Look for amplifier
degradation. Improperly configured amplifiers can degrade digital data
signals. The larger the network, the higher the possibility of amplifier noise
affecting the signals.
5. Be aware of thermal sensitivity: signal loss over coaxial cable is affected by
temperature. This can cause variations of 6 to 10 dB per year. The downstream
power level may need seasonal adjustment.
Resolving Cable Modem Problems
If CMs are not registering and cannot communicate with the cable interface, the
problem may be one of the following:
• Misconfigured Authentication String or Key
• CM Does Not Reply to Station Maintenance Requests
• CM is Offline
• CM Cannot Obtain an IP Address
• Provisioning Problems Cause CMs Not to Register
• CM Does Not Respond to SNMP Messages
Misconfigured Authentication String or Key
All CMs must return a known authentication text string or key to register with the
cable interface for network access. If the text string or key is improperly entered,
the CMs cannot authenticate and register with the cable interface.
Follow these steps to re-enter the shared authentication text string or key so that
the CMs can authenticate and register with the cable headend:
1. Ensure that the authentication string or hexadecimal key in the CM
configuration file matches the authentication string or hexadecimal key
configured on the CMTS. CMs cannot register with the CMTS if
authentication parameters do not match.