In smart substation, with regard to the realization of substation area backup protection (SABP) which can execute the backup protection function for whole substation, the information communication network transmitting and sharing digital signals will undoubtedly play an important role. In this paper, the realtime performance of a smart substation's process level network, which receives voltage/current sampled values (SV) message and sends generic object oriented substation event (GOOSE) message for SABP, was studied. Firstly, the structure and function of SABP were introduced, and its demands for the communication network's working performance were proposed. Besides, taking a practical 220kV smart substation for example, the process level network's structure scheme was designed for SABP, and then the time-delay characteristics of the messages including both SV and GOOSE were estimated. According to the research results, under the condition that the actuating signals of SABP come from the process level network, the time-delay characteristics of this information communication network can satisfy the requirement for the rapidity of action of backup protection. In the end, some measures which may help to reduce transmission delay further were presented in brief.