## 2 Problem Statement  
The 5G Infrastructure Public Private Partnership (5G-PPP) proposes addressing all aspects of segregation or slicing of the 5G network. A Fifth Generation Mobile Network is expected to be a multi-service network that supports a wide range of verticals with a diverse set of performance and service requirements based on the division of a single physical network into several isolated logical networks [22]. Therefore, the slicing of the network appears as an economic solution for implementing the diverse requirements of 5G and their respective verticals. Thus, 5G-PPP divides its architecture into different layers [23]. By selecting NSs, the Network Service Orchestrator, or simply the Orchestrator, is able to create a logical network with different characteristics customized to the needs of each user, ensuring parameters such as latency, bandwidth, transfer rate, security, availability, etc. [24]. Thus, the Orchestrator selects the best logical and physical networks to serve the end-user. The purpose of network slicing is to provide logical isolation and independent operations under all parts and layers of the network. An E2E NS is deployed across one, two, or several networks stretching across the RAN, transport, and core network, belonging to the same or different administrative domains. The process of establishing a multi-domain Network Slice Instance (NSI) [25] leverages the benefits of recursive virtualization, as described in [26]. The process of building the NS in 5G networks will be carried out under three main virtualized layers, namely: (i) the Service Instance Layer, (ii) the Network Slice Instance Layer, and (iii) the Resource Layer, as illustrated in Figure 1.  
A Service Instance characterizes each service, that is, an operating time construction of an end-user service or a commercial service performed within or by an NS [27]. Each service instance reflects a service provided by a vertical segment via the service provider application. The NSI represents a set of resources customized to accommodate the performance requirements of a specific service and can contain none, one, or several different Sub-Network Slice Instances (SNSIs), being isolated or shared. An SNSI can be a network function, a subset of network functions, or network resources that realize part of an instance of the NS. Each instance of the NS is established E2E and can contain distinct sub-networks--domains that are logically and/or physically isolated from another instance of the NS. In particular, resources associated with a sub-network can be used in isolation, disjunctive, or shared, following the specific policies and configuration arrangements of the NSL. An NSI, in turn, can be used exclusively by a service instance or shared between different service instances, usually of the same type. Common abstractions of relevant resources and open Application Programming Interfaces (APIs) allow dynamic control and automation of instances of Network Slices that reflect dynamic demands of services [22]. In the process of orchestrating or managing services and controlling network slicing, the NS provides E2E connectivity, allowing different network technologies to coexist in a common infrastructure and under a continuous closed-loop process that analyzes service requirements to ensure desired performance. NSs consist of Virtual Network Functions (VNFs), Physical Network Functions (PNFs), value-added services, cloud network resources with dedicated and shared software and hardware in the RAN, transport, and core networks, thus combining different technologies [22; 28]. Nevertheless, implementing E2E network slicing is a challenging objective that requires well-developed enabling technologies, global standards, and a mature ecosystem [29]. Such a paradigm can facilitate the composition of NS across different administrative borders, efficiently and flexibly combining different types of resources.