Dharam, sorry for my previous reply about the network. I must have thought I was replying to another post. The HDX will reboot when it thinks it has some sort of problem.
Typically when there is possible corruption in a config file. Another cause is errors caused by some outside source. Most common is a loose or damaged mic cable. The errors caused by a bad cable can cause a boot as the HDX is trying to clear the problem. If the cable gets jiggled the problem may go away.
If this occurs again give Polycom Support a call, we can instruct you on how to download the system Support Package which contains the logs for analysis. We can usually determine the cause from the logs.