Mohammad Asif Habibi, Faqir Zarrar Yousaf, Hans D. Schotten

• The mapping of a virtual network service onto a physical network infrastructure is a challenging task due to the joint allocation of virtual resources across nodes and links, the diverse technical  requirements of end-users, the coordination between multiple host domains, and others. This issue is exacerbated further by the extension of virtualization to the next-generation radio access network (NG-RAN) architecture and the provisioning of radio access network (RAN) slicing. To that end, this article focuses on the mapping problem of the virtual network functions (VNFs), as well as their internal and external virtual  links (VLs), of a RAN slice subnet onto intelligent points of presence (I-PoPs) and transport networks  in the NG-RAN architecture. In this context, in contrast to the majority of the state-of-the-art proposals,  which frequently fail to achieve performance objectives and neglect resource allocation constraints, this  article introduces automation and intelligence at an architectural level to map VNFs and VLs onto their  corresponding physical nodes and links, with the goal of achieving superior efficiency in virtual resource  utilization while granting the performance of a RAN slice subnet. Benefiting from a top-down approach,  the key contributions of this article are: (i) to extend the architectural framework of network slicing towards  the NG-RAN architecture and provide a comprehensive overview and critical analysis of the components  and functionalities of a RAN slice subnet; (ii) to integrate the Experiential Network Intelligence (ENI)  framework into a joint architecture of the network functions virtualization–management and orchestration  (NFV–MANO), Third Generation Partnership Project-network slicing management system (3GPP-NSMS),  and I-PoPs in order to render automation and intelligence to the management and orchestration aspects  of a RAN slice subnet in the NG-RAN architecture; and (iii) to propose a learning-assisted architectural  solution for mapping the VNFs, as well as their internal and external VLs, of a RAN slice subnet onto  the underlying I-PoPs and transport networks.