The counting and retransmission of network datagram is encapsulated in the module of network communication . this is transparent to the scada application . all what scada application to do is the invocation of the sending datagram and receiving datagram interface 网络报文的编号,报文的重传,都封装在网络通讯模块,这些对于上层的scada应用程序来说是透明的, scada应用程序只需调用网络通讯模块提供的发送和接收报文接口来接受和发送报文。