Server UDP lag issues

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http://stackoverflow.com – I've been working on a UDP android server for some time, and at last, it works, it allows multiple clients to connect, they can move their block around the screen, and everyone connected can see, but my issue is, when a client moves it is instant on their screen, but on another clients screen, it doesn't happen until about 3seconds later, now I know this is a server issue, I think I know where the issue is but I'm not sure how I can try and fix it, my server uses 3 different ports, one to receive a message so a client wants to join, one port to allow clients to send their position, and one mor (HowTos)