2 or 3 digits for the Mobile Network Code (MNC), and the next 9 or 10 digits for the Mobile Subscriber Identification Number (MSIN). For privacy reasons, the SUPI from the 5G devices should not be transferred in cleartext and is instead concealed inside the privacy-preserving SUCI. The SUPI is privacy-protected over the air of the 5G RAN by using the SUCI. For SUCIs containing IMSI-based SUPIs, the UE, in essence, conceals the MSIN of the IMSI. On the 5G operator side, the Subscription Identifier De-concealing Function (SIDF) of the UDM is responsible for the de-concealment of the SUCI and resolves the SUPI from the SUCI based on the protection scheme used to generate the SUCI. The DNN performs the same function and follows the same format as the Access Point Name (APN) in 2G, 3G, and 4G systems. End-to-End Architecture Components, Concepts, Security, and Transport ACCESS POINT NAME 2G/3G/4G (APN) APN Network Identifier Identifies the Data Network APN Operator Identifier Identifies the PLMN DATA NETWORK NAME (DNN) Figure 2.24 - The DNN The DNN is essential for the UE to be able to identify to which network it needs to connect for a particular type of service. Common use cases are accessing the internet and the ability to place voice calls. In this case, the UE would need to connect to a mobile network, requesting access to DNN data (for internet access) and the DNN IMS (for voice, video, and text services). Hence, two PDU sessions will be established, one with DNN data and one with a DNN IMS. Similarly, there can be other DNNs based on advanced 5G use cases, such as having a DNN for enterprise connectivity or for IoT devices. Summary In this chapter, we went over the various 5G NFs and some 5G concepts. The concepts discussed in this chapter will be the foundations on which we will explore 5G deeper and the various procedures and deployment options. In upcoming chapters, we will deep-dive into the cloud-native and service-based infrastructure and go into details of various 5G procedures, call establishment, and S