Simultaneous TCP Open

Question

I am implementing "simultaneous TCP Open".That means both peer will try to connect each other at the same time. I confused whether listen is rquired or not in this case.

or tell me the sequence of socket need to be called for each client.

I am implementing this for TCp hole Punching.

thanks,

Answer 1

From Wikipedia's article on TCP hole punching:

Because both parties are connection TO each other (e.g. 2 x CONNECT(), no LISTEN(), ACCEPT(), etc.) to generate OUTBOUND traffic there is however a problem with:

TCP Sequence numbers

Acknowledgment numbers

The required state is just like after the three-way-handshake: Each host must have an acknowledge number == other sequence number + 1. This is achieved through Sequence and Acknowledgement Number coordination.

listen() is not needed. The sequence depends on what is available.