## 4 Standardization of 5G Network Slicing Energy Efficiency KPIs
#### 5.2.2 Network Slices Realized as Network Subnets  
In the previous examples, hard network slicing is presented, where the NS resources are entirely used in the communication service taking place between the UE and the VNF of the server, which serves one NS in the access, transport, and core network elements, and thus NS resources cannot be shared among different NSs. Therefore, each NS is tied to the specific service that is offered to the users through the exploitation of network resources solely by this NS. This approach to creating network slicing is one of the possible approaches to setting the 5G sliced network. In addition, 3 GPP TS 28.530 [16] states that different NSs can use the common subnet in the access or core part of the 5G network. Figure 11 illustrates the core and access network parts of the 5G network that constitute specific NSs for illustrative purposes. In this case, different parts of the NS subnets can be used in different parts of the 5G network (access or core).  
In the case of the example in Figure 11, there are three NSs (NS1, NS2, and NS3) with three communication services on Servers 1, 2, and 3, which are offered to the three different groups of users--UE1, UE2, and UE3, respectively. The services are realized through NS1,  
Figure 11: Multiple communication services realized through multiple network slices [16].  
Figure 10: Allocation of network elements (NEs) in the 5G network with two network slices for the case of: (**a**) traffic increase in NS 2; (**b**) traffic decrease in NS 2.  
NS2, and NS3, and their corresponding subnets span over different parts of the access and core network (Figure 11). The 3 GPP standardization presents the possibility of more than one NS using one subnet in the access or core part of the network at the same time (e.g., NS2 and NS3 use the same subnet in the 5G access network, as illustrated in Figure 11). This example of soft network slicing opens further opportunities for reducing energy consumption in the 5G network. Two or more NSs sharing the same network resources enables better 5G network resource exploitation and opens the possibility of putting more 5G network elements in the sleep (energy-saving) operation mode.  
An interesting case of using such soft network slicing to achieve possible improvements in the 5G networks' energy efficiency appears in the example, presented in Figure 11, where a communication service offered by Server 2 to the user's group UE2 utilizes the core and access network resources of two NSs (NS1 and NS2). In the case of a traffic scenario where a low traffic volume of NS2 is transferred over the 5G network during a certain period(s) of the day, there is potential for energy savings to be achieved by putting NS2 core network subnet elements into sleep mode, while the communication service of NS2 between the UE2 and VNFs of Server 2 can be transferred over the core network subnet of NS1. In this case, the NS1 core and access network subnet need to adapt their capacities to ensure an appropriate QoS for NS2 and its own NS1. This opens a new field of research dedicated to the development of algorithms for the dynamic activation and deactivation of parts of the core or transport/access networks that serve specific NS according to variations in the traffic intensity of specific NS services. In the next section, some of the possible approaches to improving 5G network energy efficiency through the dynamic adaptation of network resources in network slicing are presented.