You should have both games "handshake" at the beginning of the game. They both essentially agree on a time to use. Both clients should also checkup on the other clients to assure they are playing by the rules. For instance, if the other player sends a move outside of their timeframe, my client would receive the command and should reject it. From there, you can either have error control code or trigger a game "out of sync" error. This post is from -- http://socoder.net/index.php?topic=2067