[SR-Users] Phones losing registration.

Hello, I am running into a problem with my set up. I have Kamailio 4.0 set up with an Asterisk server (ARA). Initially I had three machines; one for Kamailio, one for Asterisk and one for my db. The set up worked fine for about a week after which I saw that my phones were losing registration for prolonged periods and then would re-register after a few hours. So what I did was to move Asterisk and Kamailio on the same server and only had my DB on a separate machine. All worked well for about a week and now I am facing the same issue.  At any given time all my services ( kamailio, Asterisk, RTPproxy) are all running. My question is where and how do I start to trouble shoot this issue? I have not really done any debugging in the past so I would appreciate any pointers as to where to start? Thank you for your help. Regards, Arun