Page 83 - ITU-T Focus Group IMT-2020 Deliverables

ITU-T Focus Group IMT-2020 Deliverables 3

Figure 6.1.1-3 – Initial access

1) The UE sends and attach Request including the IMSI if a Temporary ID for the UE is not available. If
the Temporary ID is available, the UE includes the RRC layer message at least the Routing field of
the Temporary ID, so that the RAN can route the message to a suitable handler in the core.
If the UE request an initial set of slices, it can do so by indicating a Requested MDD. The Requested
MDD may also be included in the RRC layer to further enhance the routing of the Attach in the event
the Temporary ID was not available to the UE or the Temporary ID was not assigned by the same
PLMN the UE is in not belonging to the network. The MDD in the RRC layer may also be included to
enable the access to a suitable RAN slice.
2) The RAN forwards the Attach Request to the Core based on the routing criteria outlined in step 1. If
the IMSI is present a default handler is selected, Otherwise the Front end (i.e. the per UE common
NG2+NAS Signalling Handler) associated to the Temporary ID is used if available in the Serving PLMN.
If not a default front end is used. A UE should, based on configuration, not attach with a Temporary
ID that does not belong to the current PLMN.
3) The NAS Handler may execute security procedures.

4) If the UE is successfully validated, its subscription data is checked and the Handler decides the initial
set of slices the UE can use based on an evaluation of the Requested MDD, subscribed MDD and UE
capabilities. The following applies:
– If the UE did not provide the Requested MDD, the network assigns the UE to the default slice(s)
– If the UE did provide the Requested MDD, the network assigns the UE to the slices the UE is
authorized to use among the requested slices
– If some Default Slice was missing from the requested MDD, the UE is also assigned to these
slices

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