# Validating a 5G-Enabled Neutral Host Framework in City-Wide Deployments
## 3 Overview of Neutral Host Framework
### Orchestration & Control Layer  
The Orchestration & Control layer is the logical core of our neutral host framework [27] composed of multiple functional blocks for control, management, and orchestration across its 3-tier architecture. A _Dashboard_ with a Graphical User Interface (GUI) and a component for _Authentication_, _Authorization_, _and Accounting_ (_AAA_) are placed at the northbound side, to facilitate the interaction between infrastructure owners and tenants and to enforce the required security and billing. Network slices of different tenants are properly separated for security reasons, and the full isolation of information and data is preserved.  
The _Slice Manager_ has a central role in the platform, especially in the provision of the required logic for dynamic creation and management of slices. Each slice is defined as a collection of logical network partitions or chunks, combined with the network services deployed on top of them [46]. Apart from managing the registration of infrastructure resources and the creation and removal of chunks and slices, the _Slice Manager_ performs several automated tasks seamlessly, to:  
* Activate deployed slices by launching required servers (i.e., mobile core for serving cellular network slices and DHCP servers for IP assignment of Wi-Fi slices), together with the corresponding configuration of radio access chunks.
* Perform required postinstantiation configurations to deploy VNFs, in terms of enabling external connectivity, registering tasks and alerts for monitoring purposes (in the _Monitoring_ component), and DNS deployments.
* React to triggered alerts to conduct the corresponding actions (as established by the _SLA Manager_[47]), such as horizontal scaling of specific VNFs.  
To compute the optimal allocation of VNFs to be deployed over a given slice, a _Resource Placement_ component is also provided. In essence, this component determines the most suitable VNF-to-compute-chunk mapping by taking into consideration the service requirements and the resources usage.  
The orchestration capabilities of the presented platform are extended to support NFV/MEC integration following the ETSI MEC specification [24] by complementing the NFVO with MEC components that handle Mobile Edge (ME) applications [28]. In particular, the MEC Application Orchestrator (MEAO) enables the definition and management of ME platforms, applications, and services running on different mobile edge hosts. Likewise, the ME Platform components not only manage the MEC services but also handle the notifications when there are changes in the management of a given ME application or service. Hence, the _Multitier Orchestrator_ component [29] is included to provide an abstracted view in front of multiple underlying orchestrators.  
Additionally, this platform also enables virtual RAN slicing and RAN function virtualization for 5 GNR, LTE, and Wi-Fi. To do so, _SDN-based RAN controllers_ are placed beneath the aforementioned components to manage the radio components and enforce many of the required actions. To support multiple underlying RAN controllers and technologies, the _Infrastructure Abstraction_ module is located as an intermediate component between the _Slice Manager_ and the underlying SDN controllers.