Understanding FCSDK Logging

Traffic Logs
Currently, as of FCSDK 3.1.2 release, the server side traffic logs completed call statuses have the following meanings...

BROWSER_HANGUP - Browser end hangs up call normally 

BROWSER_UNAVAILABLE - Browser endpoint not found

BROWSER_BUSY - Browser endpoint engaged

BROWSER_TIMEDOUT - The browser failed to send a required (non media) message within the timeout. 

SIP_HANGUP - Sip end hangs up call normally

SIP_BUSY - Sip endpoint engaged

SIP_NOMATCH - The offer, answer, or offer request does not relate to a new session or match an existing sessions.

SIP_NOTFOUND - Call failed as the outbound request failed because the callee could not be found at the supplied address. i.e 404 response

SIP_FAILED -  Call failed with some other 4XX response

SIP_ERROR - Some unknown failure occurred on the server which may cause the call to fail including sip 5XX errors

SIP_REFUSED -  Call can't connect, sip endpoint refused an initial offer

MB_NO_MEDIA_BROKERS - No media broker available, Badly configured or Off line.

SIP_TIMEOUT - Call ended normally due to no media from browser end (Note: The sip end times out waiting for browser media. This may be clearer if labelled BROWSER_MEDIA_TIMEOUT)

Note: When a SIP_TIMEOUT is reported in the traffic log a corresponding message is reported in the app server server.log...
       sending browser error FAILED No Media was received in the configured time

Client Logs

We don't have a list of internally logged messages within our client SDKs. However both Android and IOS SDKs do provide network callback methods that you can log your own messages to.
For both IOS and Android the network call backs are listed in the developer guide.