The public network should be connected to the intranet. Campus network is an intranet, that is, an internal local area network, but it must have a public interface with the outside world, which is the public network interface. Public network is a network composed of local area networks all over the world, that is, the Internet. Education Network is a network different from Internet, also called public network, just like the internal network built by educational institutions in China, which is the communication link between educational institutions in China.