# On the Rollout of Network Slicing in Carrier Networks: A Technology Radar
## 5 CN Domain
### Add-on Features
* **Multiple slices per UE**: though 3 GPP Rel-15 specifications allow a device to connect up to eight slices at the same time, thanks to the introduction of URSP (see Section 3.1) the reality is that most Rel-15 commercial solutions do not allow this feature. The existing limitations in commercial 5G SA handheld terminals prevent an UE from being connected to more than one slice at the same time. These limitations bet on the device's Operation System (OS) [29]. The device's OS mediates between the application clients and the device's modem, where the URSP is installed. Operators, vendors, device manufacturers and chipset providers are working together to find workarounds, with de-facto solutions currently being assessed in different PoCs. Among these solutions is the 5G slicing support in Android 12(S) devices, announced by Google in October 2021. ([[https://cloud.google.com/blog/topics/telecommunications/5g-network-slicing-with-google-android-enterprise-and-cloud](https://cloud.google.com/blog/topics/telecommunications/5g-network-slicing-with-google-android-enterprise-and-cloud)]([https://cloud.google.com/blog/topics/telecommunications/5g-network-slicing-with-google-android-enterprise-and-cloud](https://cloud.google.com/blog/topics/telecommunications/5g-network-slicing-with-google-android-enterprise-and-cloud)), accessed on 20 October 2021). * **Secondary authentication**: Network Slice Specific Authentication and Authorization (NSSAA) attribute is defined in the GST [21] to specify whether, for a network slice, registered devices need to be authenticated by an external AAA server (Authentication, Authorization, Accounting server) using credentials different than the ones used for the primary authentication. This add-on feature, first introduced in 3 GPP Rel-16 specifications, is intended for those industry customers that want to perform a second authentication over their subscribers. Operators are conducting bilateral trials with customers to help them understand the value of integrating NSSAA in B2B category 5 GC slices, especially when used in the context of PNI-NPNs. In these trials, the operator-owned 5 GC's NSSAA Function [52] contacts with the customer-owned AAA server via an AAA proxy. For further details on this interaction, see [10; 30]. Finally, in the longer run (i.e., explore ring in the radar), the integration of Rel-17+ features into the 5 GC will allow operators to unleash the full potential of 5 GC slicing. In this scouting phase, operators are have set their sights on these two featured solutions. * **Slice Roaming**: operators are expected to support roaming for network slicing, at least for network slices deployed from S-NESTs. However, this feature is still years away from being in commercial networks, as there are technical and commercial aspects that need to be agreed upon. The technical aspects are discussed in [53], a GSMA document where operators have captured their priorities on slice roaming so as to guide the specification of normative solutions in 3 GPP. The commercial aspects include charging, billing and business models that are still under discussion. Unless all these aspects are agreed and reported, no multi-operator trials are expected shortly. * **NSACF**: the Network Slice Access Control Function (NSACF) is a Rel-17 5 GC function that monitors and controls (i) the number of registred UEs per network slice, and (ii) the number of PDU sessions per network slice [10]. With the NSACF, operators can enforce quotas on individual slices, making sure the signalling traffic and packet flows do not exceed the maximum slice load. NSCAF is still in stage 2 (functional definition), so no vendor solutions are yet available. In the mean time, operators are now trying to understand how to best apply this functionality to improve internal network operation, and how to link them with the admission control functionality at the NG-RAN side.