Without seeing a complete session report, I can only look at the symptom you presented. Sometimes, for example, there is a previous error, where the end result was a timeout
However, my main approach for a few years in dealing with Timeout issues is to Implement KeepAlive. I woud do this on both the Exchange server, and on the Media Agent you are backing up to
I wrote a Support Tip on how to do this:
This tip was for Windows only, but, I also wrote tips for implementing KeepAlive on both HPUX and Linux if your media agent is running on one of those. When you enter the board, do a search for 'KeepAlive'