Troubleshooting guide

Troubleshooting the CMTS
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3. Inspect amplifiers if there is an attenuation problem on the upstream path.
View CMs that proceed or follow an amplifier in the upstream 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.
4. 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.
5. Inspect the upstream physical cabling and passive equipment to be sure it is in
good condition. If the problem persists, check the upstream input power-level
configuration.
6. To adjust the upstream input power level in relative mode, use the cable
upstream power level default command in Interface Configuration mode, as
shown in the following example:
RDN(config-if)#cable upstream <n> power-level default <offset>
where:
n is the number of the upstream port
offset is the number of dB above or below the default input power level
7. To set the upstream input power level in absolute mode, use the cable
upstream power level command in Interface Configuration mode, as shown
in the following example:
RDN(config-if)#cable upstream <n> power-level <power>
where:
n is the number of the upstream port
power is the input power level expressed in dB
Resolving Problems on the Downstream Path
When the downstream port fault LED is red, the downstream port is not operating
and is not sending data to the CM subnetwork.
Refer to the procedures in this section to troubleshoot a downstream port problem: