Hi Gupta,
I can't really give recommendations on how to trouble-shoot this. The possibilities where something can go wrong, are just too many... Could even be a hardware failure, like a switch, a router or a network cable somewhere that broke down. Or someone changed the configuration of the firewall, etc. etc. I don't think we can help you from remote. Best would be to open a support ticket and let the SAP network experts take a look at it. It really seems to be an "infrastructure problem", not an "ABAP Connectivity problem".
Best Regards, Ulrich