# mIoT Slice for 5G Systems: Design and Performance Evaluation
## 4 Introducing mIoT in 5G Systems
### 5 GS mIoT Slice Design  
The design of the mIoT Network Slice for 5 GS starts from the need for an innovative connection-oriented model allowing, on the one hand, to satisfy QoS requirements of mIoT services and, one the other hand, to efficiently serve massive number of connections both from CP and UP perspective. Consistently with the gap analysis described in Section 3, major enhancements are proposed on the core network side while, to handle deployment scenarios and traffic models as per Section 2, a proper configuration of 4G LTE is considered sufficient as access network. To achieve the design goals, some new concepts are introduced. First, the device class for PhDs, which identifies the communication requirements of clusters of physical devices (e.g., QoS profile, min Reliability, min Availability, supported PDN, and PDN specific requirements). PhDs belonging to the same device class are characterized by homogeneous communication requirements and hence, their data transmission requires a homogeneous treatment by the network. Second, the Virtual Device (VD) concept is introduced: a VD is a logical entity at CN side which corresponds to the aggregation of some (or all) PhDs camped on the same cell and belonging to the same device class, i.e., a multitude of PhDs belonging to the same device class are handled at CN as a single VD, whose behavior are regulated by a single state machine (like EMM and ECM state machine regulate 4G UEs). For a given device class, a maximum number U of PhDs can be associated to a VD. A VD inherits the same device class of the PhDs it is it is meant to gather. Finally, the concept of Aggregate Core Network (ACN) bearer is introduced, transporting UP data from the (R)AN UP function through the Core Network UPFs until the external PDN. An ACN bearer is associated to each VD, and it transports data from the (R)AN/PDN Gateway to the PDN Gateway/(R)AN generated by/from all PhDs composing the VD. The ACN bearer inherits the device class of the corresponding VD. In other words, the ACN bearer makes a single simplified UP for a plurality of PhDs for which data packets require the same treatment. For a given Device Class, each ACN bearer is associated to an activity time T, restarted at each data transmission. Upon T expiration, the ACN bearer is released and the VD is de-allocated. The defined Device Class, Virtual Device and Aggregate Core Network Bearer concepts are the cornerstones for the definition of a 5G mIoT network slice. From a pure architecture perspective, the proposed mIoT slice shall be composed by the interconnection of all the basic NFs defined for 5 GS. Compared to 4G LTE/EPC system and to the 5G eMBB slice defined in [11], the proposed mIoT slice differs in the CP procedures for device registration and session set up, as well as for the user plane model. Briefly, all PhDs of a given Device Class camped on the same access node are associated to a single VD, for which a single ACB from (R)AN to UPF exists to transfer UP data. Saved for the first PhD registering to the mIoT network slice, at each PhD registration, there is no need to establish any UP connection, as the registering PhD is simply associated to the VD of the corresponding Device Class, and its UP data can be carried (both UL and DL) over the ACB previously established for the VD. Hence, through a modified registration and bearer set up procedure, the concept of Device Class, Virtual Device and Aggregate Core Network Bearer can be implemented in the mIoT slice, this affecting primarily the AMF and SMF functions. It should be noted that, on access side, mIoT slice procedures at device registration are assumed the same as per the eMBB slice, as defined in [24]. As discussed in detail in Section 5.2, compared to 4G, the mIoT slice solution reduces the amount and complexity of CP signaling, as it allows to avoid the establishment of a default bearer per each PhD. Moreover, by multiplexing data of multiple PhDs into the same ACB, the solution clearly aims at a more efficient UP resource utilization.