# On the Rollout of Network Slicing in Carrier Networks: A Technology Radar
## 8 Oss Domain
### Capability Exposure  
Capability exposure represents the ability of a network slice provider to securely expose capabilities from its managed functions and services towards one or more authorized customers. These capabilities are made available for consumption through easy-to-use service APIs. When addressing customers with limited to no telco experience, it is important that the offered service APIs focus on the customer industry segment and hide the complexity of the underlying network. This requires the provider to abstract and combine low-level network APIs (e.g., 3 GPP, ETSI and IETF stage 3 solutions) into customer-facing and intent-based APIs. The importance of capability exposure in slicing environments has been already highlighted in [110; 111]. When becoming a network slice provider, the operator can leverage this feature to offer NSaaS in multiple forms, from _provider-managed slices_ (i.e., the provider is in charge of the slice operation, while the customer can merely use the network resources of the provider slice, without any further capability of managing or controlling it) to _tenant-managed slices_ (i.e., the customer takes full control of the slice, and the provider just segregates the infrastructure as required for that purpose) [112], with some variants in between. By regulating the exposure, the operator can define the visibility and the degree of control the customer can take over the slice. Figure 18 shows the logic behind the capability exposure concept. In the following, we present the service APIs we foresee the operator may offer for capability exposure. For the sake of simplicity, these APIs have been clustered into API families. Today's situation is as follows: only some operators have NSA slices, based on any of the technology solutions captured in Figure 10. These slices are rather static, with everything configured beforehand; this means that no further customization is allowed from the customer side. In this context, the only actions that the customer can take are (i) to access the operator's portfolio, browse the service offering, select the NSA slices and issue a service order; (ii) to get high-level data on NSA slice status, for the purpose of SLA assurance; and (iii) to get information about the usage of the NSA slice and components that can be charged for. All these capabilities are provided with service APIs belonging to the **Accounting, Charging and Billing** API family. As seen, the possibilities with this as-is solution is quite limited, as it only permits provider-managed slices. However, this situation may radically change with the shift towards SA networks. In the short term (deploy ring in the radar), the focus will be on premium B2C users, as noted in Figure 11. For the provision of Type A2 slices, the operator will bet on internal NESTs. With the presence of NEF in the Rel-15 5 GC solution suite, and the integration of the first Rel-15 features in their OSS systems, the operators are starting to launch a new API family: **Device Info**. It provides the customer with the ability to receive information related to one or more devices. This includes information on device subscription (e.g., subscribed NSSAI), device location tracking (UE location and cell site), device mobility (handovers), device status (e.g., serving S-NSSAI, loss of connection, etc.) or CN type change (5 GC to EPC coverage, and vice versa). This API family might offer the customer the possibility to explicitly query for this information (request-response mode) or be reported with notifications on subscribed events (subscribe-notify mode). In the medium term (the test ring in the radar), the operators will publish the NESTs into their service portfolio, once 5 GC capabilities necessary for building up B2B category slices are available. The use of NESTs provides an easy solution for the customer to request the allocation of a slice. Based on the service requirements captured in the NEST, the operator can then decide which B2B category slice is most appropriate, and provision it.