# Server Operation and Virtualization to Save Energy and Cost in Future Sustainable Computing
## 2 Background
### Synchronization of Virtual EPC Model and Virtualization Candidate Component  
Early discussions on Network Function Virtualization (NFV) dealt mainly with the reduction of equipment cost due to the use of a large amount of general-purpose hardware, increased efficiency of equipment use through the virtual network function, and reduced operation cost due to automation. Figure 3: 2G/3G Network Structure and 4G Network Structure. Upon closer inspection, however, while the equipment cost is significant, it has lower priority in the mobile core compared to other areas of the network. This is because the hardware cost of EPC accounts for about 20-30% only, and EPC has a relatively lower portion in the overall network equipment cost. In contrast, in terms of operating cost, it is absolutely beneficial if the definition of EPC is expanded to Gi/SGi application and another core virtual network. The diversity of hardware/software provided by other vendors in the mobile core network (to avoid lock-in to a specific vendor) can be solved through automation in the network function virtualization model even if it is another overhead in terms of maintenance and management. Besides the equipment cost and operating cost, potential profit from the virtual EPC includes rapid and flexible service development and application, elastic capacity adjustment, service chaining, network slice, and interlocking with SDN technology. At present, various mobile core functions are regarded as candidate components for virtualization. The entire mobile core is expected to be virtualized fully in the next few years to operate at the same level of performance and functionality as the existing EPC equipment. The mobile core functions can be classified into data flat node (S/P-GW, etc. ), control flat node (MME, Policy, IMS, etc. ), and Gi/SGi LAN function. The control flat function is mainly operated in most x86-based server platforms today. Technically, it is relatively clear and suitable for virtualization since it only needs modification to work at the virtualization hierarchy. Policy or IMS application server is considered the first function for virtualization, and mobile network service providers that have not yet secured IMS infrastructure are interested in the virtualization version. The MME function is rather different; it is the most important component in EPC functions. If there is any failure due to overload or service problem to the MME function, it leads to a critical result. Therefore, mobile network service providers or vendors seem to take a conservative stance, and the MME pulling function is highly likely to be introduced as a short-term alternative. If the usage is rapidly increased, however, it is possible to extend the capacity dynamically, and it is suitable for elasticity and failure recovery fundamentally. Thus, some network equipment vendors consider the virtual MME to be a good alternative compared with the MME pulling function in the long term. The virtualization of S/P-GW in relation to the data flat function is far more difficult than the virtualization of control flat function since stable high-speed packet processing is required. Generally, the gateway is implemented on an edge router or an Advanced Telecom Computing Architecture (Advanced TCA, Wakefield, MA, USA) platform using dedicated line cards with CPU processors to optimize data flat performance. Since multiple vendors already support multi-functions in the traditional platforms, GGSN (Gateway GPRS Support Node), P-GW, and S-GW can be set through software. It is already a kind of virtualization, and the gateway is operated in the pool in this way for N + 1 redundancy and efficiency. Therefore, technically speaking, while it is not difficult to virtualize component, it is not easy to satisfy the performance requirements of the virtual network. As such, care must be taken from the design stage. For example, in Europe's largest mobile core network, up to 50 Gbit/s traffic takes place.