Page 79 - ITU-T Focus Group IMT-2020 Deliverables

ITU-T Focus Group IMT-2020 Deliverables 3

c) If the UE has been provided a Configured or Accepted NSSAI for the ID of the PLMN that the UE
accesses, the UE provides this NSSAI in RRC and NAS as described below.
Each SM-The NSSAI in the NSSAI may include:
– Slice/Service type (SST), which refers to the expected network behaviour in terms of
features and services.
– Information that complements the Slice/Service type(s) to allow further differentiation for
selecting from the potentially multiple network slice instances that all comply with the
indicated slice/service type(s). This information is referred to as Slice Differentiator (SD).
NOTE – The abbreviation SM-NSSAI does not imply it is used only in SM procedures nor that it only
carries SM information. E.g. it may be used to help in AMF selection as part of the NSSAI.

An SM-NSSAI can include both a Slice/Service Type and Slice Differentiator or just the Slice/Service
Type.
The RAN routes the initial access to a CCNF using the NSSAI (see bullet 4 for CCNF definition).

d) If the UE did not receive any Accepted NSSAI for the ID of the PLMN that the UE accesses, the
UE provides the Configured NSSAI in RRC and NAS, if the UE has been provided with a
Configured NSSAI. The RAN uses the NSSAI for routing the initial access to a CCNF. If the UE
doesn't store any NSSAI (Accepted or Configured) for the ID of the PLMN that the UE accesses,
the UE provides no NSSAI in RRC and NAS, and the RAN sends NAS signalling to a default CCNF
(see bullet 4 for CCNF definition).
e) After (initial) slice selection, upon successful attachment the UE is provided with a Temp ID that
is provided by the UE in RRC during subsequent accesses to enable the RAN to route the NAS
message to the appropriate CCNF, as long as the Temp ID is valid. In addition the serving PLMN
may return an Accepted NSSAI that the UE stores for the PLMN ID of the serving PLMN. The
Accepted NSSAI includes the SM-NSSAI values of the slices the UE is accepted to use by the
network.
f) For a "Service Request" the UE is registered/updated and has a valid temp ID, which is sufficient
in the RAN to route the request to the serving Common CP NF. It is assumed that the slice
configuration doesn't change within the UE's registration areas.
g) For enabling routing of a TA update request the UE includes always Accepted NSSAI and a
complete Temp ID in RRC. If the RAN is aware of and can reach the CCNF which is associated
with the Temp ID, then RAN forwards the request to the CCNF. Otherwise, RAN selects a suitable
CCNF based on the Accepted NSSAI and forwards the request to the selected CCNF. If the RAN
is not able to select a CCNF based on the Accepted NSSAI, then the request is sent to a default
CCNF.
h) The UE shall include in a PDU session establishment Request a SM-NSSAI which, shall enable
the selection of an SMF, alongside the DNN.
i) In order for RAN to select a proper resource for supporting network slicing in RAN, RAN may
need to be aware of the network slices. How the RAN is aware of this is up to RAN WGs to
determine.
3) If a network deploys network slicing, then it may use UE provided network slice selection assistance
information to select a network slice. In addition, the UE capabilities and UE subscription data may
be used.
4) A UE may access multiple slices simultaneously via a single RAN. In such case, those slices share
some control plane functions, e.g. AMF and Network Slice Instance Selection Function. These
common functions are collectively identified as CCNF (Common Control Network functions).
5) The CN part of network slice instance(s) serving a UE is selected by CN not RAN.

a) The NSSF is one function of CCNF, which is a set of NFs including the AMF and the NSSF, and is
used to select the NSI for the UE.

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