The proposed ICMP normal model is defined by a maximum allowed ratio of the number of ICMP request and reply packets, since each normal ICMP message should be paired with a corresponding reply.

• 由于每个正常的ICMP消息应该与一个相应的应答配对，提出的ICMP正常模型通过ICMP请求和应答包数的最大允许比率定义。