The listener (on a specific port) waits for an incoming connection on that port and uses it to open a TCP connection on a random available port and frees up the listener for other incoming connections.
The TCP Wait On Listener VI returns a TCP Connection reference when a client connects. You pass this reference into your handler and can use it for TCP Read/Writes.
For your asynchronous communications your server would read an incoming 'message' and then probably send a reply back. If you want your server to send a synchronous message then just do a TCP Write to your client from the handler.
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