# On the Rollout of Network Slicing in Carrier Networks: A Technology Radar
## 1 Introduction  
Over recent years, the telco industry has actively focused on the exploration of technologies to accelerate the roll-out of fifth generation (5G) systems worldwide. Unlike 4G, mainly focused on providing mobile broadband services to end users, 5G has been designed from its inception to help boost the digital transformation of vertical industries (i.e., industry sectors aiming at becoming fully digital, such as manufacturing, smart cities, transportation or agriculture [1]). The direct involvement of the so-called verticals and their specific needs within the 5G technology ecosystem implies the emergence of a new wave of use cases, with very different requirements in terms of performance (e.g., throughput, latency and reliability) and functionality (e.g., mobility, security, service continuity support), some of them very stringent. To satisfy these different (and potentially conflicting) requirements in a cost-effective manner, operators need to turn their networks into programmable multi-service platforms,embracing the infrastructure and functional sharing mechanisms commonly referred to as network slicing. With network slicing, the operator's network can be logically split into a set of programmable network partitions (i.e., network slices), each designed to satisfy a particular set of service requirements. The service-tailored logical networks resulting from this partitioning can be executed in parallel, but need to be operated in isolation from each other. This means that despite running on a common (shared) network infrastructure, network slices require separate (independent) management [2]. The technology foundations for slicing are already here. On the one hand, network functions virtualization (NFV) allows deploying the functions of every slice with necessary capacity where and when required. On the other hand, software defined networking (SDN) allows operators to programmatically steer traffic within the slice, across the deployed functions. In addition to these dynamic control means, NFV and SDN technologies also provide the ability to resize and move workloads at operation time, in such a way that the service requirements can be always met, regardless of network conditions, e.g., a faulty node or traffic load surges. However, to fully exploit the benefits that network slicing brings, it is important for the operator to apply the dynamic allocation and tailored partitioning of resources at all segments, from the radio access to the data network, including all the network domains in between. This means that the slice concept shall span the entire operator's managed network infrastructure, resulting in the provisioning and operation of end-to-end (E2E) network slices. The E2E nature of slicing forces operators to keep consistency in the behaviour of individual slices along the different domains. This may bring significant operational challenges in commercial networks, as outlined below:  
* **Slicing readiness varies across the different domains**. In fact, the degree of penetration of slicing features in the different technology domains is not the same. For example, while the core network has incorporated network slicing support since the first 5G release (3 GPP Release 15), the transport network does not support any native slicing feature yet, and first solutions have only recently been integrated into the radio access network. The main reason why the maturity level varies across technology domains (and their corresponding management domains) is mainly due to the existing fragmentation in the standardization arena, with a high number of participating Standard Development Organizations (SDOs). In the current landscape, each SDO addresses a portion of the E2E problem, developing slicing specifications for this portion under assumptions that do not necessarily match the assumptions made by other standard bodies, which typically address other portions.