NG interface protocol and function between NG-RAN and 5G core network: Simple explanation is the interface between wireless access network and 5G core network.

There may be multiple NG-C logical interfaces from any NG-RAN node to 5GC. Then, the selection of NG-C interface is determined by the NAS node selection function. There may be multiple NG-U logical interfaces from any NG-RAN node to 5GC. The selection of NG-U interface is completed within 5GC, and AMF sends a signal to NG-RAN node.

Legitimacy authentication of client and server:

In this way, both parties can be sure that the data will be sent to the correct client or server. Both the client and the server have their own digital certificates. In order to achieve the purpose of authenticating users, WTLS requires both parties to exchange their respective digital certificates for identity authentication, so that the other party's public key can be obtained reliably.

The WTLS protocol for encrypted data uses both symmetric and asymmetric encryption algorithms. Specifically, before the secure communication connection is established, both parties use asymmetric encryption algorithm to encrypt the message information in the handshake process, and carry out digital signature and verification by both parties.

After the secure communication connection is established, both parties use symmetric encryption algorithm to encrypt the actual communication content to improve communication efficiency.