Following diagram illustrates the procedure of Initial
Register:
The following is performed for Initial Register:
- The AMF sends a GET request
to the NSSF. The AMF queries the NSSF, with Requested NSSAI, mapping of
Requested NSSAI to Configured NSSAI for the HPLMN, the Subscribed S-NSSAIs
(with an indication if marked as default S-NSSAI), any Allowed NSSAI it might
have for the other Access Type (including its mapping to the Configured NSSAI
for the HPLMN), PLMN ID of the SUPI, UE's current tracking area, NF type of the
NF service consumer, and AMF ID.
- Based on this information,
local configuration, and other locally available information including RAN
capabilities in the current Tracking Area for the UE , the NSSF does the
following:
- It selects the Network
Slice instance(s) to serve the UE. When multiple Network Slice instances in the
UE's Tracking Areas are able to serve a given S-NSSAI, based on operator's
configuration, the NSSF may select one of them to serve the UE, or the NSSF may
defer the selection of the Network Slice instance until a NF/service within the
Network Slice instance needs to be selected.
- It determines the target
AMF Set to be used to serve the UE, or, based on configuration, the list of
candidate AMF(s), possibly after querying the NRF.
- It determines the
Allowed NSSAI(s) for the applicable Access Type(s), taking also into account
the availability of the Network Slice instances that are able to serve the
S-NSSAI(s) in the Allowed NSSAI in the current UE's tracking areas.
- Based on operator
configuration, the NSSF may determine the NRF(s) to be used to select
NFs/services within the selected Network Slice instance(s).
- When the NSSF is able to
find authorized network slice information for the requested network slice
selection information, NSSF sends Discovery Request for AMF to NRF.
- The NRF responds with list
of candidate AMFs to NSSF.
- The NSSF returns to the
current AMF the Allowed NSSAI for the applicable Access Type(s) , the target
AMF Set, or, based on configuration, the list of candidate AMF(s). The NSSF
returns the NRF(s) to be used to select NFs/services within the selected
Network Slice instance(s), and the NRF to be used to determine the list of
candidate AMF(s) from the AMF Set. The NSSF returns NSI ID(s) to be associated
to the Network Slice instance(s) corresponding to certain S-NSSAIs. NSSF also
returns the rejected S-NSSAI(s) and the Configured NSSAI for the Serving PLMN.
