# Virtualized MME Design for IoT Support in 5G Systems
## 2 Background
### Virtualization  
NFV is one of the enabling technologies of 5G systems, because it will allow network operators to cope with challenges, such as the traffic increase and IoT support while reducing CAPEX and OPEX. With NFV, network functionalities are implemented with Commercial Off-The-Shelf (COTS) hardware, which is much less expensive than the very specialized hardware used in 4G networks. In this way, operators can create, scale and deploy network components whenever they are needed, according to the particular real-time traffic conditions. These benefits are relevant for the deployment of IoT in cellular networks. NFV could facilitate the adaptation of the network entities to the new demand. With NFV, the infrastructure services can be programmed, instead of re-architecting the infrastructure of the network [20]. In [9], the authors discuss the design of a virtualized EPC for implementation in a cloud computing environment and its offering \"as a Service\" (EPCaas). They present and analyze a number of different implementation options for the virtualized EPC. Focusing on the 1:N mapping option, each entity of the EPC is decomposed into three logical components: a Front End (FE), Service Logic (SL) and State Database (SDB). The FE acts as a communication interface with other entities of the network, for example the FE terminates Stream Control Transmission Protocol (SCTP) sessions between eNodeB and MME [21] and balances the load among several SLs. SLs implement the processing. The SDB stores the user session state, making the SLs stateless. This design follows the multi-tiered web services paradigm for cloud-based applications. Each of the three logical components is a tier of the multi-tier architecture. Figure 1: Mobile-originated data transport in the NAS packet data unit [5]. SLs are stateless, and therefore, they can scale out/in without impacting externally-connected peers and independently from other SLs. The scaling of SDB and FE, which are stateful components, is possible [22], although it requires a careful design. In multi-tiered web services, dedicated hosting refers to the case where a server is allocated to at most one application at any given time [23]. On the contrary, in shared hosting, multiple small applications share each server. Dedicated hosting is used for running large clustered applications where server sharing is unfeasible due to the workload demand imposed on each individual application. Dimensioning is the classic process to determine the amount of resources required to process a set of requests with a specific Quality of Service (QoS) target. However, dimensioning is a static process, whereas the traffic in mobile networks strongly fluctuates. However, dynamic provisioning of resources according to the fluctuations in the request rate is feasible thanks to the virtualization technologies and the wide adoption of cloud computing system infrastructures [24]. As in the case of Internet workloads, mobile network traffic exhibits long-term variations, such as time-of-day or seasonal effects, as well as short-term fluctuations caused by unexpected events. Therefore, it is reasonable to consider applying dynamic provisioning techniques of multi-tiered web services for virtualized EPC entities. In [22], the authors study the provision resources in multi-tier applications and propose a strategy to avoid bottleneck shifting. They propose to break down the end-to-end response time \(\overline{D}\) into per-tier response times \(\overline{D}_{1}\), \(\overline{D}_{2}\),... \(\overline{D}_{j}\), such that:  
\[\sum_{j=1}^{j}\overline{D}_{j}=\overline{D}. \tag{1}\]  
Then, they propose to determine how many servers to allocate to each tier separately, such that tier \(j\) processes the requests with a service response time equal to \(\overline{D}_{j}\). For this capacity prediction, an estimate of the peak session rate is used. In Section 5, we will use this strategy in the estimation of resources for the virtualized MME entity.