## 3 Protocols Analysis
### Protocols Comparison  
Table 3 compares the two standards from the main application scenarios, functions, communication methods, communication modes, frame types, timing modes, and frame rates. From the comparison in Table 3, it can be found that the functions described in IEC 60870-5-101/104 are more abundant than GB/T 26865.2-2011, and are more suitable for practical applications in the distribution network. The communication modes of IEC 60870-5-101/104 are Polling and Cycle Distance Transmission (CDT), but in practice polling communication mode is used more often, and adopts the method of actively sending changed data. The advantages of this are that the reliability of each round of transmission service is ensured and the amount of information transmitted is reduced, but the system response time increases. According to the description of GB/T 26865.2-2011, the primary station controls the sub-station by issuing a command frame. The sub-station performs transmission configuration according to the CFG-2 delivered by the primary station, so that the data upload function can be automatically completed, but the remote control is not provided. In communication mode, the command pipeline and file pipeline adopt polling, and the data pipeline adopts CDT. \begin{table}
\begin{tabular}{c l l} \hline \hline  & **ICC 60870-5-101/104** & **CB/T26865.2-2011** \\ \hline \multirow{3}{*}{Application scenarios} & The main station in SCADA monitors and controls terminal units, such as remote terminal unit/distribution terminal unit/feeder & Real-time data and historical file transfer between main station and main station, between main station and sub-station in the real-time terminal unit (RTU/DTU/FTU) \\ \cline{2-3}  & Link reset, link request, lock synchronization, file transfer, & System reset, turn data transmission on/off, remote trigger, \\ \cline{2-3}  & & parameter loading, total summon, group summoning, transmission \\ \cline{2-3}  & & metric, sequence of event (SOE), command, remote control & parameter configuration (CFG-1/CFG-2) and confirmation \\ \hline \multirow{2}{*}{Connecting pipeline} & Single pipeline & 3 pipelines: command, data, file \\ \cline{2-3}  & & Serial communication & TCP/IP-based network communication \\ \hline \multirow{2}{*}{Communication method} & Piling & Command pipeline and file pipeline adopt polling, data pipeline \\ \cline{2-3}  & CDT & adopts CDT \\ \hline \multirow{2}{*}{Frame type} & Variable length frame, fixed length frame & Data frame, configuration frame, head frame, command frame, file \\ \cline{2-3}  & & transfer command frame, event identification frame, file transfer \\ \hline \multirow{2}{*}{Real-time data} & Telemetry, telesignalization, remote control information, Total & Status, phasenor, frequency offset, frequency change rate, analog, digital, configuration information, command \\ \cline{2-3}  & & Fixed point data, remote operation data, alarm data, extremum data, \\ \cline{2-3}  & Offline file & reactive power compensation data, statistical data, fault record data, \\ \cline{2-3}  & & electric energy \\ \hline \multirow{2}{*}{Timing mode} & Network time & GPS/BDS \\ \cline{2-3}  & Frame rate & 0.1–1 frame/s & 25, 50, 100 frames/s \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of protocols. In the communication method, IEC 60870-5-101 uses serial communication, and IEC 60870-5-104 and GB/T 26865.2-2011 use network communication based on transmission control protocol/internet protocol (TCP/IP). For the international protocol IEEE C37.118.2-2011 similar to GB/T 26865.2-2011, it can adopt the same serial communication method as IEC 60870-5-101, and can also choose IP-based network communication, including TCP, user datagram protocol (UDP), and a combination of TCP and UDP. Therefore, in the choice of the communication method of the extended protocol, it is not necessarily limited to the use of TCP, and the communication method based on TCP/UDP can be flexibly combined, so that the advantages of TCP and UDP can be fully utilized.