Port Knocking with IP Tables

Can some one please help me here. Using iptables commands, create a port knocking system that will open up port 22 (SSH) through the firewall when the remote host “knocks” on ports 2222 , 3333, and port 4444 , and all ‘knocks’ within 60 seconds. After that, the port (22) should be open through the firewall for 45 seconds.