1.　　算法原理：当发送IP包时，需要计算IP报头的校验和：当接收IP包时，需要对报头进行确认，检查IP头是否有误，算法同上2、3步，然后判断取反的结果是否为0，是则正确，否则有错。

2.　　实现功能：计算输入数据的校验和，以判断接收数据是否正确

-1. Algorithm principle : When sending IP packets, it needs to calculate the IP header checksum : When receiving IP packets. need to confirm reported first check whether the IP header error, the algorithm ditto two, three steps, then obtain judgment against the results of 0, it is correct, otherwise it is not true. 2. Implementation functions : calculate the checksum data entry and to judge whether the data correctly