## Priority-Based Protocol Extension Method
### Data Flow Calculation Method  
Without the method of this paper, the data frame length calculation equation is as follows:  
\[L_{\text{data}}=F_{1}+P+A+D \tag{4}\]  
In Equation (4), \(L_{\text{data}}\) is the total length of the data frame, and \(F_{1}\) is the base length of the data frame and its value is the total bytes of the SYNC, FRAMESIZE, IDCODE, SOC, FRACSEC, and CHK fields in the data frame. \(P\) is the length of real-time data, whose value is the total bytes of STAT, PHASORS, FREQ, and DFREQ fields in the data frame. \(A\) is the length of analog quantity and its value is the length of the ANALOG field in the data frame, and \(D\) is the length of digital quantity, whose value is the length of the DIGITAL field in the data frame. In order to ensure the uniform transmission of data, the method of sending each data frame separately to avoid frames is adopted. Considering that the maximum segment length \(L_{\text{MSS}}\) of TCP without options is 1460 bytes, when \(L_{\text{data}}\) exceeds \(L_{\text{MSS}}\), the data frame requires multi-TCP frame transmission. The calculation equations of the amount of data transmitted per unit time are as follows:  
\[L_{\text{data}}=L_{\text{MSS}}n+L_{x} \tag{5}\]  
\[M_{\text{data}}=[L_{\text{data}}+L_{\text{net}}(n+1)]R_{\text{data}} \tag{6}\]  
In Equations (5) and (6), \(n\) and \(L_{\text{x}}\) are the quotient and remainder of \(L_{\text{data}}\), respectively, divided by \(L_{\text{MSS}}\); \(M_{\text{data}}\) is the total amount of real-time data transmitted per unit time; \(L_{\text{net}}\) is the network transmission base length, and its value is the length sum of the Ethernet frame preamble, Start of Frame Delimiter (SFD), Ethernet header, 4-byte Cyclic Redundancy Check (CRC), IP header (IPv4, without TCP option), and TCP header length; and \(R_{\text{data}}\) is the data frame transmission rate, indicating the number of frames sent per unit time. Figure 6: Remote control process. After adopting the method of this paper, if all the analog quantities and digital quantities are separated into the application extension frame transmission, the frame length calculation equation is separated into the following three equations:  
\[L_{\text{new-D}}=F_{1}+P \tag{7}\]  
\[L_{\text{YC}}=F_{2}+A_{\text{INF}} \tag{8}\]  
\[L_{\text{YX}}=F_{2}+D_{\text{INF}} \tag{9}\]  
In Equations (7)-(9), \(L_{\text{new-D}}\) is the total length of the data frame after the method is used; \(L_{\text{YC}}\) is the total length of the application extension frame for transmitting telemetry information; \(F_{2}\) is the base length of the extended frame of the application, and its value is the length sum of the \(F_{1}\), TYPE, VSQ, RtnR, and Add fields in the extended frame; \(A_{\text{INF}}\) is the length of the INF field containing the full analog; \(D_{\text{INF}}\) is the length of the INF field containing the full digital; and \(L_{\text{YX}}\) is the total length of the application extension frame for transmitting telesionalization information. The method in this paper also needs to ensure the uniform transmission of phasor data. The calculation equations of the average transmission amount of data per unit time are as follows:  
\[L_{\text{new-D}}=L_{\text{MSS}}n_{1}+L_{\text{x1}} \tag{10}\]  
\[L_{\text{YC}}=L_{\text{MSS}}n_{2}+L_{\text{x2}} \tag{11}\]  
\[L_{\text{YX}}=L_{\text{MSS}}n_{3}+L_{\text{x3}} \tag{12}\]  
\[L_{\text{data}}=L_{\text{MSS}}n+L_{x} \tag{5}\]0  
The meanings of \(n_{1}\) and \(L_{\text{x1}}\) in Equations (10)-(12) and the calculation are the same as for formula (5); \(M_{\text{new}}\) is the total amount of real-time data transmitted per unit time after adopting the method; \(R_{\text{YC}}\) is a fixed transmission rate for the application extension frame for transmitting telemetry information; and \(V_{\text{YC}}\) is the frame rate average change value of the application extension frame for transmitting changed telemetry information.