## 3 Network Slicing in 5G Networks  
### 5G Network Slicing Architecture from the Perspective of Energy Efficiency  
Network slicing is a concept in which multiple logical networks exist in one physical infrastructure in such a way that existing networks do not overlap while providing all functionalities as if they were established on separate physical networks. In the 3 GPP specification [16], an NS is conceptualized as a logical network that is designed to offer specific capabilities and characteristics, accommodating a range of service properties tailored for customers utilizing NSs. According to [17], the concept of network slicing is based on different network resources that are sliced and allocated to each NS. Therefore, the NS is a specific set of network resources allocated to the UEs or use cases. The NS is thus a logical approach to allocating network resources along the data path into multiple network sets, which are optimized for specific use cases or groups of UEs. Network slicing allows different services to coexist on a common physical infrastructure. The dynamic nature of network slicing enables real-time adaptation to changing network conditions and service requirements. This adaptability is essential for providing reliable and high-quality services in dynamic environments. Each NS acts as an isolated entity, thus ensuring that the performance and security of one slice do not affect the others. Every NS can be generally characterized by the following parameters:  
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2. Throughput: for the services specific to the NS, each slice should have a designated portion of throughput reserved for itself. 3. Topology: every NS is expected to possess a unique perspective on the network elements and the interconnections that bind these elements together. 4. Resources: every NS needs to have a guaranteed share of computational resources (processors, storage, communication links, physical networking elements, etc.) that can be used for NS service offerings. 5. Memory: since different NSs have different storage needs, memory resources need to be allocated according to the requirements of each NS. 6. Traffic forwarding: an NS needs to enable the extension of its service area, utilizing forwarding routing tables and other networking resources at the control layer. 7. Traffic type: specific traffic of the same type can be grouped and assigned to a single NS, which needs to ensure its complete isolation from the rest of the network and better overall resource utilization. The main concept behind network slicing, as shown in Figure 3, is built upon a framework of three distinct layers, as follows: the service instance layer, network function/slice instance layer, and infrastructure/resource layer [18]. **The service instance layer** is the layer that includes the services or virtual functions offered by the operators, enterprises, or third-party vendors that can be directly accessed by end users or businesses (Figure 3). Each distinct service is represented by a service instance that contains the operations system support (OSS) and business system support (BSS) elements of the service offered through NS. The service instance layer makes the lowest direct contribution to the overall NS energy consumption; however, the OSS/BSS politics and practices of the subject that offers specific services in NS can have an indirect impact on the NS instantaneous energy consumption and its future trends. The **NS instance layer** is the layer that involves the instances of network slices that can be deployed (Figure 3), and includes elements related to the user and control plane functions, equipment configuration policy, and NS life cycle management. A network slice instance provides the required network features for the associated NS service instance's functionality.