The following procedure is used by LMF to collect GNSS assistance information from AFs via the NEF.
For trusted AFs, LMF collects GNSS assistance data through AFs directly. LMF discovers trusted AFs covering LMF serving area through NRF and subscribes to GNSS assistance data exposure from discovered trusted AFs.
AF invokes Nnrf_NFManagement_NFUpdate_request service operation to register its GNSS related information including Event IDs, and associated AF identification, Application ID(s) and its serving area (TAs). NRF stores the received AF update information and sends Nnrf_NFManagement_NFUpdate_response message to AF.
When LMF needs to discovery the available GNSS assistance data from AFs, LMF provide TAs to NRF through Nnrf_NFDiscovery service to discover related AFs.
LMF subscribes to or cancels subscription to GNSS assistance data in AF by invoking the Naf_EventExposure_Subscribe/Naf_EventExposure_Unsubscribe service operation.
AF notifies the LMF with the available GNSS assistance data by invoking Naf_EventExposure_Notify service operation. AF also provides associated serving area (TAs) of the GNSS assistance data and optional precise global coordinates of the source of the GNSS assistance data. The AF notifies the LMF with the data by invoking Nnef_EventExposure_Notify service operation.
After LMF gets the GNSS assistance data, it can send the data to UE via the procedures described in clauses 6.14
during a positioning session.