Network coverage can be divided according to a local area network (LAN), a metropolitan area network (MAN) and wide area networks (WAN).
The OSI reference model communication function of the entire network is divided into seven layers, from low to high respectively are: physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer.
Strict peer communication layer, like the same protocol layer.
Network layer address is a network address and a host address portion of the address consisting of the two, the network address is globally unique.