server(Port) ->
{ok, Socket} = gen_udp:open(Port,[binary]),
loop(Socket).

loop(Socket) ->
    receive
       {udp, Socket, Host, Port, Bin} ->
           BinReply = 'A REPLY GOES HERE',
           gen_udp:send(Socket, Host, Port, BinReply),
           loop(Socket)
    end.