Asterisk calls dropping

I keep having dropped calls on my asterisk server at different time intervals into a call. I am prepared to do a trace/dump of a call, and provide any trunk parameters so that you can analyse the source of the problem. As its a LIVE server, I cannot provide direct access, so I will have to be directed as to what variable (etc) to modify to effect the fix. I am not prepared to upgrade my Asterisk 1.6.1.13 implementation.