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The smart grid features ubiquitous interconnections of power equipments to enable two-way flows of electricity and information for various intelligent power management applications, such as accurate relay protection and timely demand response. To fulfill such pervasive equipment interconnects, a full-fledged communication infrastructure is of great importance in the smart grid. There have been extensive works on disparate layouts of communication infrastructures in the smart grid by surveying feasible wired or wireless communication technologies, such as power line communications and cellular networks. Nevertheless, towards an operable, cost-efficient and backward-compatible communication solution, more comprehensive and practical understandings are still urgently needed regarding communication requirements, applicable protocols, and system performance. Through such comprehensive understandings, we are prone to answer a fundamental question, how to design, implement and integrate communication infrastructures with power systems. In this paper, we address this issue in a case study of a smart grid demonstration project, the Future Renewable Electric Energy Delivery and Management (FREEDM) systems. By investigating communication scenarios, we first clarify communication requirements implied in FREEDM use cases. Then, we adopt a predominant protocol framework, Distributed Network Protocol 3.0 over TCP/IP (DNP3 over TCP/IP), to practically establish connections between electric devices for data exchanges in a small-scale FREEDM system setting, Green Hub. Within the real-setting testbed, we measure the message delivery performance of the DNP3-based communication infrastructure. Our results reveal that diverse timing requirements of message deliveries are arguably primary concerns in a way that dominates viabilities of protocols or schemes in the communication infrastructure of the smart grid. Accordingly, although DNP3 over TCP/IP is widely considered as a smart grid co- munication solution, it cannot satisfy communication requirements in some time-critical scenarios, such as relay protections, which claim a further optimization on the protocol efficiency of DNP3.