5.5 LI service discovery

33.1273GPPLawful Interception (LI) architecture and functionsRelease 18TS

In SBA as defined in TS 23.501 [2] the NRF is a central repository of discoverable NFs. For NFs to be discoverable, they need to have been previously instantiated and undergone a degree of configuration (function identity allocated, IP addresses, certificates, network connectivity to NRF, etc.).

LI functions (e.g. ADMF, POIs and MDFs) exist within a separate security domain to the main network NF to which they are embedded. Furthermore, as with legacy networks, LI functions associated with NFs shall be configured and tested before the associated NF is allowed to enter active network user service (i.e. LI shall be configured and tested before an NF can handle live user traffic).

In the present document, all LI functions have dedicated LI_X interfaces and discovery of LI functions by the LIPF shall happen as part of the NF / LI function instantiation phase. POIs, TFs and MDFs shall not be subject to or within the scope of NRF service discovery as defined in TS 23.501 [2]. The SIRF is used to provide the LIPF with NF discovery information which shall be used to identify which NFs are applicable to intercept specific user sessions, as described in clause 5.3.6. However, the SIRF is not involved directly in LI service discovery.

The SIRF may be used to inform the LIPF that an NF has been registered / deregistered with the NRF and is now ready for use in a network user service. The LIPF is assumed to already have knowledge of which POIs and TFs are associated with which NFs.

POIs, TFs and MDFs may be discovered in virtualised deployments using the approach described in clause 5.6. The exact mechanisms for achieving this are out of scope of the present document.