It is a crucial problem to rationally design the topological structure of the substation communication system in developing future digital substations in order to achieve data sharing and enhance the reliability of the protection and control system. The main techniques of the process bus are described and two methods of realizing publisher/subscriber communication for sampled value（SAV） and generic object-oriented substation event（GOOSE） messages are proposed. Three kinds of busbar protection communication architectures based on different process buses are presented and simulated in OPNET Modeler. The results show the feasibility of these communication architectures. The applicable scopes of different communication architectures are discussed after comparison， which may be valuable for design of the process level communication network.