# Virtualized MME Design for IoT Support in 5G Systems
## 2 Background  
### Internet of Things  
The convergence of the digital and the physical world provided by the Internet of Things (IoT) allows the interaction between the environment and the devices connected to the network that collect information. Under this umbrella, many applications can be envisaged, which have led to several markets (verticals) for IoT. In IoT applications, machines (or devices) connected to the network can communicate among them, or with the application server, without human interaction. This is known as Machine-to-Machine (M2M) communications. IoT applications are designed for specific verticals, such as industry (e.g., monitoring industrial plants, boarding operation), energy (e.g., inventory, waste collection), automotive (e.g., bike sharing, parking system), healthcare (e.g., diagnostics, mobile assistance) or media and entertainment (e.g., payment systems, comfortable living) [12]. These verticals have different requirements that determine IoT applications' design, as for example, the particular connectivity needs, device energy consumption, capabilities, security or traffic characteristics. Despite there being many possible requirements for IoT applications, M2M communications used in IoT are being classified by organizations, such as the 3 GPP or the Mobile and wireless communications Enablers for the Twenty-twenty Information Society (METIS), in two big trends [13], based on their Quality of Service (QoS) requirements:  
* Massive M2M (mM2M): characterized by low cost/energy devices, small data volumes and a massive number of devices connected. Among others, relevant examples are smart metering, fleet tracking or building automation. * Low latency M2M (IM2M): characterized by strict requirements, such as ultra reliability, low latency and high availability. The distinct requirements depend on the specific application. For instance, the end-to-end latency can reach down to a few milliseconds or even lower [14]. To achieve that, low latency services could be served by different core entities in the network. For simplicity, we assume that the IM2M devices considered in this work can be handled by the MME. Industrial monitorization, security or healthcare, and tactic Internet are examples of this trend. For most of M2M communications used in IoT applications, small and infrequent data transmissions are a common traffic characteristic, as mentioned in [15]. Nevertheless, this traffic characteristic is handled inefficiently by current mobile networks, such as LTE. This is mainly due to the prior resource reservation required before the transmission [16]. To solve that, the 3 GPP has included LTE enhancements for M2M in its specifications, recently integrated into the context of Cellular IoT (CIoT). For example, the 3 GPP has introduced in [5] new procedures to reduce signaling to transfer data packets from or to the device, named data transport in Control Plane CIoT Evolved packet system Optimization (CPCEO). To this end, the procedures use Non-Access Stratum (NAS) transport capabilities. In LTE, NAS is used to transfer non-radio signaling between the User Equipment (UE) and the MME. In the transmission of uplink data, with this new procedure, the data packet is sent as NAS signaling by the UE to the MME after Radio Resource Control (RRC) establishment. Next, the MME carries out the security check, and then, it forwards the data packet to the Serving Gateway (SGW) (see Figure 1). The CPCEO procedures avoid the establishment and release of data plane bearers for small and infrequent packets from M2M devices, but the MME has to process these packets from the data plane transmitted as NAS signaling. In the LTE Evolved Packet Core (EPC) architecture, the MME deals with the control plane. That is, this entity is the main signaling node in the EPC. Its main functions are: NAS signaling, user authentication, mobility management (e.g., paging, user tracking) and bearer management. For more information about the MME entity, see [5].