Section: 6.1.2 Requirements 6.1.2.1 General
Content: The serving 5G network shall support providing connectivity to home and roaming users in the same network slice. In shared 5G network configuration, each operator shall be able to apply all the requirements from this clause to their allocated network resources. The 5G system shall be able to support IMS as part of a network slice. The 5G system shall be able to support IMS independent of network slices. For a UE authorized to access multiple network slices of one operator which cannot be simultaneously used by the UE (e.g. due to radio frequency restrictions), the 5G system shall be able to support the UE to access the most suitable network slice in minimum time (e.g. based on the location of the UE, ongoing applications, UE capability, frequency configured for the network slice). 5G system shall minimize signalling exchange and service interruption time for a network slice, e.g. when restrictions related to radio resources change (e.g., frequencies, RATs). For a roaming UE activating a service/application requiring a network slice not offered by the serving network but available in the area from other network(s), the HPLMN shall be able to provide the UE with prioritization information of the VPLMNs with which the UE may register for the network slice. The 5G system shall be able to minimize power consumption of a UE (e.g. reduce unnecessary cell measurements), in an area where no authorized network slice is available. When a UE moves out of the service area of a network slice for an active application, the 5G system shall be able to minimize impact on the active applications (e.g., providing early notification). NOTE 1: Various methods can be used to detect whether the UE moves toward the border area and to notify the UE. The 5G system shall support a mechanism for a UE to select and access network slice(s) based on UE capability, ongoing application, radio resources assigned to the slice, and policy (e.g., application preference). The 5G system shall support a mechanism to optimize resources of network slices (e.g., due to operator deploying different frequency to offer different network slices) based on network slice usage patterns and policy (e.g., application preference) of a UE or group of UEs For UEs that have the ability to obtain service from more than one VPLMN simultaneously, the following requirements apply: - When a roaming UE with a single PLMN subscription requires simultaneous access to multiple network slices and the network slices are not available in a single VPLMN, the 5G system shall enable the UE to: - be registered to more than one VPLMN simultaneously; and - use network slices from more than one VPLMN simultaneously - The HPLMN shall be able to authorise a roaming UE with a single PLMN subscription to be registered to more than one VPLMN simultaneously in order to access network slices of those VPLMNs. - The HPLMN shall be able to provide a UE with permission and prioritisation information of the VPLMNs the UE is authorised to register to in order to use specific network slices. NOTE 2: The above requirements assume certain UE capabilities, e.g. the ability to be connected to more than one PLMN simultaneously.