# Virtualized MME Design for IoT Support in 5G Systems
## 8 Conclusions  
In this paper, we propose two designs for a virtualized MME, which aim at facilitating IoT support in 5G systems. The first proposed design partially separates the processing resources devoted to each traffic class; while the second design includes traffic shaping to control the traffic of each class.  
We have considered three traffic classes: MBB, massive M2M and low latency M2M. In M2M communications, we have included M2M events to analyze the performance of the virtualized MME. M2M events considered are caused by the report synchronization of massive M2M devices and alarm events of low latency M2M devices. Additionally, we assume the use of the CPCEO procedure to transfer these reports from M2M devices.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline SchemeTier & Number of FE Instances & Number of SL Instances & Number of SDB Instances \\ \hline BS & 1 & 5 & 1 \\ \hline OS & 2 & 13 & 2 \\ \hline TS & 2 & mM2M & 4 & 1 \\  & & lM2M & 1 & \\ \hline SS & 2 & 7 & 1 \\ \hline \hline \end{tabular}
\end{table}
Table 7: vMME model dimensioning at the simulation point.  
Figure 13: CDF of the filtered vMME delay for each scheme (ten M2M devices per MBB UE). (**a**) Baseline scheme; (**b**) Overdimensioned scheme; (**c**) Traffic separated scheme; (**d**) Traffic shaper scheme.  
We have compared our proposed designs with two other schemes: (i) a baseline virtualized MME design, which does not apply such resource separation; (ii) an overdimensioned virtualized MME.  
The reported comparisons include: (i) dimensioning of the required resources; (ii) estimation of the costs based on the model of Amazon EC2; (iii) the evaluation of the response time of the virtualized MME schemes for each traffic class.  
After the conducted simulations, the results show that our proposed schemes provide much lower costs than the overdimensioned scheme while they satisfy the exigent delay requirements of MBB and low latency M2M communications. Furthermore, the comparison of the traffic separation scheme and the traffic shaper scheme shows that the multiplexing gain of the latter provides benefits in terms of latency reduction. However, the traffic separation scheme enables one to have different delay requirements for each traffic class, and additionally, it can isolate their performance.  
In addition to the above results, we identify the following advantages of the considered solution: (i) CPCEO procedures mitigate the signaling explosion generated by a huge number of M2M connected devices. However, it increases the processing load on the control plane of the EPC. (ii) NFV increases the scalability of the network to deal with such load increase of signaling. (iii) The usage of our proposed schemes further optimize the costs while satisfying the delay demands.  
However, our solution has also the following implications: (i) the dimensioning of the resources is more complex; (ii) CPCEO procedures use the transport network of the control plane to send data packets, which imposes an additional load. Furthermore, regarding the bottlenecks of the proposed schemes, the state database tier is critical. This is due to the state database scaling with certain constraints, and our solution makes heavy use of it. Moreover, the service logic tier design is determinant, as it considerably affects the performance of each traffic class.