Multiplayer in Android

I am developing an android game wherein four player will connect to each other, the player must be only be on the same LAN or Network.

My problem is I really don't know where to start? Whenever I searched in google. I didn't get the answer I need that why asking here.

I need to connect the four player with each other REAL TIME without using ONLINE SERVER. Players must be on the same network to discover each other (They should be connected to the same wifi)

Can you suggest where to start? thanks I know this is not really a question. Any suggestion or help is appreciated

Cheers, NDEVS