Page 501 - 5G Basics - Core Network Aspects

Core network aspects 1

When the UE is acting together with the network, the handover decision process begins when the UE reports
a list of alternative access points to the HDC-FE. The UE may indicate its preference at this time regarding
which entity makes the handover decision and which entity actually triggers the handover. Based on the
information the UE has provided, the HDC-FE requests RACF to check network resource availability on the
potential path through each candidate network and receives the resource check result from RACF. The HDC-
FE then responds to the UE, indicating its choice of deciding entity and triggering entity. If it has chosen the
UE to make the decision, it returns a candidate access point list which is based on the UE's input but reflects
the results of the resource check and perhaps of local policy. If it has chosen to make the decision itself, its
response includes no candidates.
The next step depends on which entity the HDC-FE has nominated to make the handover decision. If it is the
HDC-FE, then the HDC-FE retrieves static network information for the candidate access points from the NID-
FE. Based on that information, it makes a final decision on the identity of the target access point. It prepares
for handover to that target access point as described in the next two clauses. It then informs the UE of its
decision. The UE responds when it is ready for the handover. Alternatively, the UE may respond that
handover to the selected access point is not possible (e.g., because it is no longer 'visible' to the UE). In this
latter case, the whole network discovery and decision process must begin again.

If the UE is the one to make the decision, it is the one to retrieve static network information about the target
networks from the NID-FE. It makes its selection, then informs the HDC-FE. The HDC-FE prepares the new
access point as described in the next two clauses, then responds to the UE.

The actual triggering of handover execution is done by the entity nominated by the HDC-FE. The complete
discovery and decision process is illustrated in Figure 7.

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