Performance of protection and control function in relay based on IEC 61850 protocol can be significantly improved with real-time data sharing among multiple bays for digital substation. To achieve it， the first challenge is to resolve the real-time sampling data sharing and communications between IEDs. In response to this question， the communication in process level is analyzed from points of network topologies with bay-oriented and same voltage level oriented respectively; the study on the process network with function-oriented is proposed， and the existing problems are also basically provided with solutions. It is concluded that the maximal number of bays with data sharing is inversely proportional to the sampling number in single bay when network flux is in the range of operation and if the message size is same in all bays. And the data sharing under 400 points sampling per cycle can be satisfied with bay-oriented and same voltage level oriented network topologies in 100 Mbit/s network; the most communication time delay and data sharing limitation is depended on performance of the switchers.