# On the Rollout of Network Slicing in Carrier Networks: A Technology Radar
## 5 CN Domain
### Functionality  
The first 5G commercial networks available worldwide are based on NSA. The reason is that most communication service providers are looking to deliver mainly high-speed connectivity to consumers already with 5G-enabled devices today. For these providers, the NSA mode makes the most sense, because it allows them to leverage their existing packet core assets (EPC) rather than deploy a completely new 5G network. In this mode, where 5 GC does not exist, there is no native slicing support, as outlined in Section 3.1. However, this lack of slicing enablers (e.g., no S-NSSAI support) does not mean the operators are unable to provide service differentiation and traffic segregation at the core side; in fact, there are a number of solutions that allow the EPC to enforce some level of traffic separation for overload mitigation when having multiple services. Figure 10 depicts a functional description of some of these solutions, tagged with **NSA slicing (pre-slicing)** wording. As seen, the capabilities across these solutions are quite different, ranging from basic QoS differentiation (e.g., QCI based common APN-S/PGW) to a complete packet core separation (e.g., DECOR [41]), with a number of variants in between, some of them subjected to technology availability. For example, NFV technology is a must for the implementation of the control user plane separation solution (Figure 10E). As communication service providers set their sights on new revenue streams from groundbreaking 5G services (i.e., uRLLC, mIoT, V2X services), they realize the need to migrate to the SA mode, which represents the target 5G system architecture [42]. With the first commercial 5 GC solution suites already available in the market, operators can bring native slicing functionality into their carrier-class facilities. Despite being Rel-15 compliant, these first solution suites typically provide very limited capabilities in relation to S-NSSAI support; in fact, many of them offer single-slice support, with their AMF/SMF implementations only able to deal with one S-NSSAI at a time. The fact that one single slice can be configured in the 5 GC prevents the operator from using separate slices to achieve service/customer traffic segregation. In these circumstances, non-NSSAI assisted solutions shall be used instead. One example is the provisioning of separate Data Network Name (DNN) [10] for different services/customers. This **DNN-based solution** is equivalent to the pre-slicing solution shown in Figure 10B, where virtual APN/QCI (EPC artifacts) are now replaced with DNN/5 QI (5 GC artifacts). With the ever-increasing adoption of DevOps practices in the telco industry, 5 GC software may be developed, delivered, tested and brought into operation incrementally at a far higher cadence than it was before. The CI/CD pipeline [43] will allow vendors to reduce time-to-market and shorten release cycles in their product roadmap. Based on this rationale, it is expected that first 5 GC solution suites will be quickly upgraded with new features, including multi-slice support in AMF/SMF. This feature allows the configuration of two or more slices in the same 5 GC, by fetching associated S-NSSAIs from the NSSF and injecting them into the corresponding AMF/SMF instances. The ability of having multiple 5 GC slices (CN slice subnets) running in parallel may offer operators greater possibilities to tap new 5G use cases targeting public network users (B2C market) and industry companies (B2B market). These customers may have different service requirements in terms of performance and functionality, hence the need to define different 5 GC slice types for them:  
1. Business-to-Customer (B2C) slice types, used for serving traffic from user-centric applications. Figure 10: Different deployment options for NSA slicing. (**A**) QCI based common APN-S/PGW. (**B**) Virtual APN/QCI based on Charging Characteristics (CC). (**C**) Dedicated S/PGW. (**D**) DECOR. (**E**) Control User Plane Separation.