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When the UDP protocol modules receive packets, first locate the port fields of UDP packets, save the remote and purpose port of the UDP packets, then the compare the objective port of the packet with the port of local regulations, if not equal, discard it; if equal, call the cor-responding function. Finally, set the source port, objec-tive port, data length, checksum field in the header of UDP packet, add datum to be sent, make encapsulation and sending by IP layer. The processing flow of UDP protocol is shown in Figure 6.

4.5 The Implementation of TCP Protocol

Due to the limited resources of singlechip, and to handle TCP packet better, so while implementing the TCP pro-tocol module, we reduced the common TCP/IP protocol, and did not implement the sliding window protocol, flow control and congestion control mechanisms. Meanwhile, we set two TCP connection control block in the TCP protocol modules, and adopt the response mode with single window. When receiving TCP packets, first locate mark field of TCP packets, if the TCP packet is required to build a new connection, check whether still exist spare TCP connection control block in the system. If present, this spare control block will be used as the control block for this connection, and establish connections. Con-versely, if there is no spare TCP connection control block, and do nothing.

When the mark field of the TCP packets is another type, search whether exist TCP connection control block corresponding to the TCP packets. If present, judge ac-cording to the mark field of the value of SYN, FIN, ACK and so on, then choose corresponding function to process packets. If don't exist TCP connection control block cor-responding to the TCP packets, don't do anything. Construction and closing the connection of the TCP protocol are through the \\spe-cific wave\the specific approach. The proc-essing flow of TCP protocol is shown in Figure 7. 5. Testing

In order to test whether the TCP/IP protocol realized can achieve the desired objective, we carried on a series of tests.

The Ping command is the most frequently used in network. This command sends

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