Importance of ping - pong in udp p2p communication

Question

I am quite new to socket programming. I was trying to make p2p communication using udp and did finally made it. While writing a program, the point I have observed is that communication between two peers does not take place if packets are not send from both sides. I read somewhere that in networking its called ping-pong.

I want to know why it is designed like that?

Answer 1

The issue you encountered is likely due to firewalls and NAT routers.

The solution is to use NAT traversal techniques (Most useful information is the various techniques listed under See Also).