Synchronous system and method for processing a packet

A packet processing method, comprising:

• providing a plurality of packet processing devices and at least a switch;
• having said plurality of packet processing devices to synchronously receive a packet having a sequence number and a security parameter index from said switch;
• having said plurality of packet processing devices to synchronously record said sequence number on a table;
• locating a security association according to said security parameter index;
• selecting one of said plurality of packet processing devices according to a load balancing mechanism to continue to process said packet though said security association;
• and
• delivering said packet to a destination wherein said load balancing mechanism comprises:
• assigning a packet processing priority order to said plurality of packet processing devices;
• processing a plurality of said packets by using said plurality of packet processing devices in said packet processing priority order, and storing in each of said plurality of packet processing devices a data amount of each of said plurality of said packets;
• and assigning a new packet processing priority order to said plurality of packet processing devices according to a cumulative data amount stored in each of said plurality of packet processing devices, such that the lower the cumulative data amount, the higher a new priority position in said new packet processing priority order is given to a particular one of said plurality of packet processing devices with the cumulative data amount, and repeating said processing step by using said plurality of packet processing devices in said new packet processing priority order.