A scheme of distribution terminal unit accessing spdnet

This paper describes a method to solve the problem that IP address pool is too small in the SPDnet access layer by introducing “The Private Network” into SPDnet , such as internal server PAT mapping technique. It is the critical practice that distribution local communication network acts as the private network, only IEC 60870-5-104 protocol's service port (2404) are permitted to open, and it is forbidden that Distribution Terminal Unit in the distribution local communication network actively initiates connection to SPDnet. The method can effectively control the business data to access SPDnet from distribution local communication network, and can reliably ensure the security of SPDnet.