# mIoT Slice for 5G Systems: Design and Performance Evaluation
## 4 Introducing mIoT in 5G Systems  
### The 5G System Architecture  
The definition of a customized CP and UP to efficiently support mIoT services, based on an innovative connectivity model overcoming 4G limitations, is made possible within 5G system (5 GS) thank to the architecture modularization and the support of network slicing. Figure 2 shows the 5 GS reference architecture (as agreed by 3 GPP in [14]). 5 GS has been decomposed into a set of Network Functions (NFs), which can communicate either via point-to-point interfaces or via service-oriented interfaces, the latter illustrated in the figure. Without entering into excessive details, it is essential to highlight the role of some NFs. The Access and Mobility function (AMF) terminates the CP interfaces with the (R)AN (N2) and with the UE (N1), and manages UE registration, mobility, reachability and security. The Session Management function (SMF) manages the UE connectivity towards the User Plane functions (UPFs), which terminate the UP interface towards the (R)AN (N3), act as mobility anchor, and terminate the interface towards external Data Networks (N6).  
Unlike 4G system, for which a single and monolithic architecture is defined, 5 GS can support different network slices, i.e., different complete logical networks whose different architectures are defined by the interconnection of different set of customized CP and UP NFs. Network slices are defined \"end to end\" (i.e., including access and core network) and hence the customization of NFs can relate also to the access network: network slices can be differentiated at the access and the \"R\" between brackets aims to stress different access networks can be integrated in 5 GS, including legacy RANs and non-cellular networks (e.g., non-3 GPP access). Different network slices can be deployed over different infrastructure and can be independently accessed by different devices. When registering to the 5G network, UEs shall indicate the network slice(s) they will request service(s) from, and they  
Figure 2: 5G System Reference Architecture. NEF: Network Exposure Function; NRF: Network function Repository Function; PCF: Policy Control Function; UDM: Unified Data Management; AF: Application Function; AMF: core Access and Mobility management Function; AUSF: Authentication Server Function; SMF: Session Management Function; UE: User Equipment; (R)AN: (Radio) Access Network; UPF: User Plane Function; DN: Data Network.  
will be authorized or denied the registration according to their credentials. Upon a service request for a given network slice from a UE, the AMF will route CP signaling to the CP NFs of the concerned slice and, likewise, a UP connection for the concerned network slice will be established including the relating (R)AN and UPF(s). This way, CP and UP will be fully customized on per network slice basis, via a dedicate design of the relating CP NFs and UPFs.  
Within this reference framework, crystalized in 3 GPP release 15 specification [14], multiple challenges will stem out in the coming years, i.e., how 5G architecture and procedures shall look for each network slice, to optimize performance, network efficiency and resource utilization for the related use cases.  
Within the 5 GS reference architecture, an mIoT network slice has been designed and is described in the following sections, overcoming the key limitations of 4G systems. It is important to observe that for 5 GS defined by 3 GPP release 15, commonly denoted as 5G phase 1, only eMBB slices are specified. mIoT slices will be specified by 3 GPP release 16, for which the solution proposed by this paper could be a possible candidate. The design is based on the concepts of Virtual Device and Aggregate Core Network Bearer, which are implemented via a proper customization of AMF and SMF, as described in Section 4.2.