## 2 Preliminary
### 5G SA CN Protocol Message  
When it comes to 5G CN protocols, the NSA architecture uses lower-layer UDP and upper-layer GTP-C protocol stacks and lower-layer SCTP and upper-layer diameter protocol stacks [20]. On the other hand, the SA structure allows CN functions to use HTTP/2 protocols with JSON, based on SBA. As the protocol dedicated to sending and receiving messages between CN functions was changed to HTTP/2, the burden of data transmission weighs heavier than in the use of traditional GTP-C protocol since individual transfer size is bigger and the messages to create a session are larger in number. When UE registers with the 5G CN, HTTP/2 and PFCP messages are sent as shown in Figures 3 and 4. In this regard, we counted the number of messages in protocols HTTP/2 \begin{table}
\begin{tabular}{l l l} \hline \hline
**Functions** & **Full Name** & **Description** \\ \hline \multirow{2}{*}{AMF} & Access and mobility & 5G core network function manages mobility, \\  & Management Function & registration, connections, reachability \\ \hline \multirow{2}{*}{SMF} & Session Management Function & 5G core network function that handles \\  & & subscriber session management \\ \hline \multirow{2}{*}{UPF} & User Plane Function & 5G core network function that aids in packet \\  & & routing/forwarding and connecting to the \\  & & DN (Data Network) in relation to the UE’s \\  & & UP (User Plane) data \\ \hline \multirow{2}{*}{PCF} & Policy Control Function & 5G core network function that controls \\  & & integrated policy on the behavior of the 5G \\  & & core network in its entirety and delivers \\  & & policy to other control plane NFs \\ \hline \multirow{2}{*}{NSSF} & \multirow{2}{*}{Network Slice Selection Function} & 5G core network function that supports \\  & & selection of the optimal network slide \\  & & available for the service requested by the user \\  & & and provides supportable AMF information \\ \hline \multirow{2}{*}{AUSF} & \multirow{2}{*}{Authentication Server Function} & 5G core network function that provides \\  & & authentication and security features for UEs \\  & & connected to the 5G core network \\ \hline \multirow{2}{*}{UDM} & \multirow{2}{*}{Unified Data Management} & 5G core network function for the storage and \\  & & management of user subscription data and \\  & & authentication data \\ \hline \multirow{2}{*}{NRF} & \multirow{2}{*}{Network Repository Function} & 5G core network function that performs \\  & & managing functions for monitoring service \\  & & status of 5G core NFs and interworking \\  & & information such as authentication and \\  & & tokens of authority \\ \hline \multirow{2}{*}{NEF} & \multirow{2}{*}{Network Exposure Function} & 5G core network function that supports \\  & & functionalities of storing internal or external \\ \multicolumn{2}{c}{} & service functions and events in structured \\ \multicolumn{2}{c}{} & data, exposing network capabilities to the \\ \multicolumn{2}{c}{} & application function, and allowing the AF to \\ \multicolumn{2}{c}{} & access the services \\ \hline \hline \end{tabular}
\end{table} 
Table 1: CN functions defined by 3 GPP. and PFCP being generated when registering one UE in the 5G SA architecture. As a result, it was found that a total of 4 HTTP/2 messages are generated during the authentication procedure on the registration flow. Moreover, when assuming that a user generally uses the internet, voice call, and text messaging services, a total of 3 packet data units (PDUs) per service are activated. n HTTP/2 message for the establishment of 3 PDU sessions generates a total of 24 messages made up of 8 messages per PDU session. Additional messages exist for the PFCP. It generates a total of 12 messages, with each PDU session composed of 4 messages. To put together both HTTP/2 and PFCP, one UE triggers 40 CN protocol messages in total. As for the de-registration procedure, on the contrary, HTTP/2 generates a total of 18 messages made up of 6 messages per PDU session, to remove the PDU session.