The internetwork interconnect allows secure communication between service-consuming and a service-producing NFs in different PLMNs. Security is enabled by the Security Edge Protection Proxies of both networks, henceforth called cSEPP and pSEPP respectively. The SEPPs enforce protection policies regarding application layer security thereby ensuring integrity and confidentiality protection for those elements to be protected.
It is assumed that there are interconnect providers between cSEPP and pSEPP. The interconnect provider the cSEPP's operator has a business relationship with is called cIPX, while the interconnect provider the pSEPP's operator has a business relationship with is called pIPX. There could be further interconnect providers in between cIPX and pIPX, but they are assumed to be transparent and simply forward the communication.
The SEPPs use JSON Web Encryption (JWE, specified in RFC 7516
) for protecting messages on the N32-f interface, and the IPX providers use JSON Web Signatures (JWS, specified in RFC 7515
) for signing their modifications needed for their mediation services.
For illustration, consider the case where a service-consuming NF sends a message to a service-producing NF. If this communication is across PLMN operators over the N32-f interface, as shown in Figure 13.2.1-1
below, the cSEPP receives the message and applies symmetric key based application layer protection, as defined in clause 13.2
of the present document. The resulting JWE object is forwarded to intermediaries. The pIPX and cIPX can offer services that require modifications of the messages transported over the interconnect (N32) interface. These modifications are appended to the message as digitally signed JWS objects which contain the desired changes. The pSEPP, which receives the message from pIPX, validates the JWE object, extracts the original message sent by the NF, validates the signature in the JWS object and applies patches corresponding to the modifications by intermediaries. The pSEPP then forwards the message to the destination NF.
The N32 interface consists of:
N32-c connection, for management of the N32 interface, and
N32-f connection, for sending of JWE and JWS protected messages between the SEPPs.
The application layer security protocol for the N32 interface described in clause 13.2
of the present document is called PRINS.