started unicast maintenance ranging - no response received

The logs are Values read by technicians from the internet provider end, since the logs are what the coaxial cable transmits and the log screen on the router is the translator so can be easily read by them, the coaxial cable is owned by the Internet service provider, I wouldn't be able to tell you what that means.

If your Event Log is reporting a high volume of errors, this would indicate a potential CMTS signal issue. To troubleshoot these errors, we would like to note the current signal levels being used by your SB8200. Please follow the steps mentioned on the below article to check the details

http://arris.force.com/consumers/articles/General_FAQs/SB8200-Cable-Signal-Levels