port 3306 disconnecting frequently

our redhat server port 3306 getting disconnected on and off while we are connecting from application server to database server.....
the iptables on both servers are disabled,., even then the port is getting disconnected if there is no activity from client nodes......
howerver, the connection getting restored after using curl command on application server....and once again if there is no activity, it is getting
disconnected......
whether there are any parameters in server system to be fixed?? pl.. guide
server information:
RED HAT ENTERPIRSE LINUX 6
APACHE SERVER 2.2.15
PHP 5.6.18
attached the screen shot