Are "Unicast Maintenance Ranging" and "ToD" errors standard?
 

I'm having terrible intermittent connectivity problems with my broadband, and on visiting the cable modem's "event log" I can see that I get the following errors every 15 seconds or so.

Time Not EstablishedTime Not EstablishedCritical (3)Started Unicast Maintenance Ranging - No Response received - ...

Time Not EstablishedTime Not EstablishedError (4)ToD request sent- No Response received

Time Not EstablishedTime Not EstablishedError (4)Config file does not include a valid CVC!

What do these errors mean, and is it normal for the modem to not know what time it is? Does this suggest some underlying problem?