# Validating a 5G-Enabled Neutral Host Framework in City-Wide Deployments
## 2 Background on Neutral Host Concept and Enabling Technologies  
The 5G technology is increasing network convergence, flexibility, and mobile broadband capacity in response to the growth in number and diversity of consumers, industries, and service demands in society [2; 12]. However, without network infrastructure sharing [13; 14], deployments of 5G networks in dense environments will not be feasible and sustainable because it will require hundreds of isolated access networks, which is unrealistic.  
A neutral and sliceable 5G infrastructure is a promising solution for network infrastructure sharing challenges [10; 15]. From a user's point of view, the system behavior and services using the resources of a neutral host should be available without user intervention and, ideally, these should be seamless and identical to those provided by their hosted clients'dedicated resources. This concept was around for some time, but within 5G ecosystems it cannot exploit its full potential due to:  
* An increasing need for enhanced and ubiquitous connectivity in urban context coupled with more demanding requirements of radio coverage and bandwidth.
* The pivotal role within 5G of smart cities, in which municipalities may act as potential 5G neutral host providers.
* A neutral host framework is a perfect candidate to fully satisfy the 5G requirements for different use cases (e.g., eMBB, URLLC, mMTC) concurrently deployed over a shared infrastructure.  
The neutral host model has an important business dimension focused on the creation of new Service Level Agreements (SLAs) categories to rule the interactions between the host and content/service providers [16; 17]. A key enabler of the neutral host model is a flexible and automated network slice allocation allowing programmability of policies according to the created SLAs, while enforcing dynamic up/down scaling decisions of infrastructure resources, assigned to service providers. As such, a tenant uses the neutral host framework to establish end-to-end segmented slices, representing partitions of the network, storage, and computing resources. In turn, those slices are leased to service providers to operate allocated resources for the mapping of their services.  
Indeed, a neutral host framework provides automated or dynamic multi-tenancy by combining a wide range of well-known technical enablers via end-to-end network slicing. While network slicing is not new in the academia and industry community, the 5G technology and the neutral host model are revitalizing the interest from the community by extending it to the next level [18].  
The Next Generation Mobile Networks (NGMN) [15] redefines the classical network slicing of a single virtual network (e.g., Layer 2 (L2) Virtual Local Area Networks (VLANs) [19], Layer 2 and Layer 3 (L2-L3) Virtual Private Networks (VPNs) [20]) to an end-to-end network slicing formed by several virtual networks mapped across cloud, edge, and RAN infrastructures. Later, the 3 rd Generation Partnership Project (3 GPP) with its standard [21] and the European Telecommunications Standards Institute (ETSI) NFV division with its standard [16] extended the NGMN definition of network slicing as a set of Network Services (NSs) interconnected by VLANs representing slices (or resource segments) from multiple infrastructures.  
Overall, end-to-end network slicing in 5G requires an NFV Management and Orchestration (MANO) solution to deploy Virtual Network Functions (VNFs) on cloud/edge resources and a virtualized RAN solution to slice and control the radio resources [22].