Page 80 - ITU-T Focus Group IMT-2020 Deliverables

3 ITU-T Focus Group IMT-2020 Deliverables

6) With reference to Annex D: move forward with Group B type of solution in rel-15 (Group C is
subsumed under Group B). Group A is not pursued in R15.
7) It shall be possible to handover a UE from a slice in NGC to a DCN in EPC. There is not necessarily a
one-to-one mapping between slice and DCN.
8) The UE need to be able to associate an application with one out of multiple parallel established PDU
sessions. Different PDU sessions may belong to different slices.
9) The UE may cause the network to change the set of network slices it is using by submitting in an MM
procedure the value of a new NSSAI. The final decision is up to the network.
The network, based on local policies, subscription changes and/or UE mobility, can change the set
of network slices that are being used by a UE by providing the UE a notification of Accepted NSSAI
change. This then triggers a UE initiated MM procedure including in RRC and NAS Signalling the new
value of the new accepted NSSAI the network has provided.
Change of set of slices used by a UE (whether UE or Network initiated), may lead to CCNF change
subject to operator policy.
NOTE – The scenarios and which MM procedures to use when such UE triggered network slice
change is to be used is to be determined during normative phase.
NOTE – Changing the set of network slices accessible by the UE will result in termination ongoing
PDU sessions with the original set of network slices if these slices are no longer used (Some slices
are still retained, potentially).
10) The Network subscription data includes information about what slices a UE is allowed to access.
a) The Information in the subscription includes both SST and SD information for each slice the UE
is allowed to access (SD information is present if applicable for a slice). This is also the SM-NSSAI
for the slice.
b) The subscription data include information on whether a slice is a default slice (i.e. the UE shall
be using this slice when it is attached to the network). When a UE is initially attached to the
network without providing any NSSAI, the CN should use a default NSSAI, composed of the SM-
NSSAI values stored in the UE subscription with a flag indication they are to be considered
default slices, to determine the default initial network slice(s set) to serve the UE.
11) During the initial Attach procedure, in case the CCNF to serve the UE is to be redirected, the CCNF,
which first receives the initial Attach request, shall be able to redirect the initial Attach request to
another CCNF via the RAN or via direct signalling between the initial CCNF and the target CCNF. The
redirection message sent by the CCNF may include an information about the new CCNF to serve the
UE.
12) For a UE that is already registered, the system shall support a redirection of a UE from its serving
CCNF to a target CCNF.

a) The operator policy determines whether redirection between CCNFs is allowed.
b) When the network decides to redirect the UE due to NSSAI change, the network send the
updated/new NSSAI to the UE using an MM procedure and an indication for the UE to initiate
an MM procedure with the updated/new NSSAI. The UE then initiates an MM procedure with
the updated/new NSSAI.
13) The network operator may provision the UE with network slice selection policy (NSSP). The NSSP
includes one or more NSSP rules each one associating an application with a certain SM-NSSAI. A
default rule may also be included which matches all applications and contains a default SM-NSSAI.
The UE uses the NSSP to associate UE applications with SM-NSSAIs. When a UE application
associated with a specific SM-NSSAI requests data transmission, then:
a) If the UE has one or more PDU sessions established with this specific SM-NSSAI, the UE routes
the data of this application in one of these PDU sessions, unless other conditions in the UE
prohibit the use of these PDU sessions. If the application provides a DNN, then the UE considers
also this DNN to determine which PDU session to use.

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