Content for  TR 22.835  Word version:  18.2.0

5GC is connected to NG-RAN and the NG-RAN supports both E-UTRA and NR. However, for a third party who wants to utilize a network slice, the different potential and flexibility of E-UTRA and NR is not something that can easily be disregarded. Also, the unequal possibility of radio resource slicing for NR and E-UTRA leads to a unique use case scenario.

Figure 5.4.2-1 shows the use case scenario where an NG-RAN is supporting both NR and E-UTRA radio resources.

In this Figure, it is assumed that

• Subscription:
  • UE A1 and A4 are subscribed to a service using Slice M.
  • UE A2 and A4 are subscribed to a service using Slice N.
  • UE A3 is subscribed to a service using Slice O.
• Deployment:
  • E-UTRA is configured to serve Slice M, e.g. for general eMBB services, including a slice for IMS service.
  • NR is configured to serve Slice N and O, e.g. for URLLC or V2X. Due to demanding requirements of V2X application, V2X application providers (e.g. OEM) requests to use only NR for Slice O.

The frequencies used for E-UTRA and NR can be the same or different. For example, when DSS (Dynamic Spectrum Sharing) is used, the same frequency is used for both E-UTRA and NR, but in different time slots.

The following is an example service flow based on the setting in the previous section:

• After power-on, UE A1, A2, A3 and A4 start searching for cells.
• UE A1, A2, A3 and A4 start registration in the found cells.
• Depending on factors such as e.g., use of Dual Connectivity, priorities of network slices, different UEs may camp on different RATs. For example, the UE A1 may camp on E-UTRA.
• Based on the various inputs, for the transport of user traffic for a network slice, the RAT and radio resources can be configured. For example, when user traffic for slice M is generated for UE A4, the network may configure E-UTRAs resource for the UE to deliver the traffic. For this UE A4, when user traffic for slice N is generated, the network may configure NR resources for the UE. When both NR and E-UTRA resource are configured, the user traffic for the network slice only flows over the allowed RATs.
• When service policy changes, e.g. when slice M is now set to use NR instead of E-UTRA, UEs camp NR cells instead of E-UTRA cells. For a UE with ongoing active communication, handover occurs to move the UE from E-UTRA to NR.

The following Figure 5.4.4-1 shows the status at the end of the service flow. For the transport of user traffic, UE A1 is served by E-UTRA, UE A2 and A3 are served by NR. UE A4 may camp on either E-UTRA or NR during Idle mode and be configured with E-UTRA, NR or both depending on the active application during Connected mode.

TS 22.261 contains many requirements related to user traffic management and network slices.

The following new requirements can be derived from this use case: [PR.5.4.6-1]

A UE subscribes to multiple network slices from its home operator. The home operator has agreements with various other operators to support the same slices for roaming UEs. In this case, the most preferred VPLMN in a specific area does not support all the needed slice; however, a second VPLMN does support the slice not available in the most preferred VPLMN. In this case, the home operator can provide the necessary information to allow the UE to use the second VPLMN to obtain the service available on that network slice, while otherwise being served by the most preferred VPLMN. Figure 5.5.1-1 illustrates the scenario.

In this scenario, the UE A1 is roaming in an area covered by 2 VPLMNs, Network A and Network B. UE A1 subscribes to services that require use of slices M and N in its home network. The corresponding slices and services are available in the visited area, even though these slices are not offered by the same network in the visited area. Network A is the most preferred VPLMN in this area.

When UE A1 first enters the visited area, it registers with Network A and can uses services from slice N. At a later time (T2), the user decides to activate a service that needs slice M. The UE, detecting that slice M is not available on Network A, looks for the network that provides the slice. The UE registers on Network B and the user is able to use the service of slice M. When the service concludes and slice M is no longer needed (T3), the UE returns to Network A.

The user is able to access all their subscribed services while roaming, even though the needed slices are not available on a single VPLMN.

Roaming and slice access work as usual, with the addition of being able to change VPLMNs to gain access to a slice not available on the most preferred VPLMN.

[PR.5.5.6-1]

A UE has access to multiple network slices when on the HPLMN. When the UE is roaming and the VPLMN where the UE is currently registered only provides a subset of the network slices that the UE needs to use, the UE can connect to other VPLMNs at the same time to access the other subscribed network slices.

• UE is subscriber of Operator Toffee
• When on its home network, Operator Toffee, UE has access to three network slices: (A)pricot, (B)anana and (C)herry
• UE runs different applications that require the UE to simultaneously access Apricot, Banana and Cherry slices
• Operator Toffee has agreements with:
  • Operator Chocolate to support Apricot and Banana slices
  • Operator Fudge to support Cherry slice
• Operator Chocolate is the preferred roaming network
• UE moves out of Operator Toffee's coverage area, into an area where the coverage is provided by Operator Chocolate and Operator Fudge

1. UE connects with Operator Chocolate, and has access to Apricot and Banana slices
2. UE requires simultaneous access to all three slices, Apricot, Banana and Cherry, due to the different applications running on the UE. However, the VPLMN the UE is registered to, Operator Chocolate, does not provide support for Cherry slice
3. UE is authorised by the HPLMN to additionally access the Cherry slice in the Operator Fudge network.
4. UE connects to Operator Fudge's network, while retaining the connection to Operator Chocolate

Roaming UE is able to access all three network slices simultaneously from Operator Chocolate and Operator Fudge.

There are related requirements in clause 6.18 of TS 22.261 on "Multi-network connectivity and service delivery across operators": Clause 5.3.2.4 of TS 23.501 on "Support of a UE registered over both 3GPP and Non-3GPP access" indicates: Also, clause 6.3.2 of TS 33.501 on "Multiple registrations in same or different serving networks".

[PR.5.6.6-1]