Softwarization of Mobile Network Functions towards Agile and Energy Efficient 5G Architectures: A Survey <s> Grouping EPC Functions. <s> As mobile network users look forward to the connectivity speeds of 5G networks, service providers are facing challenges in complying with connectivity demands without substantial financial investments. Network function virtualization (NFV) is introduced as a new methodology that offers a way out of this bottleneck. NFV is poised to change the core structure of telecommunications infrastructure to be more cost-efficient. In this article, we introduce an NFV framework, and discuss the challenges and requirements of its use in mobile networks. In particular, an NFV framework in the virtual environment is proposed. Moreover, in order to reduce signaling traffic and achieve better performance, this article proposes a criterion to bundle multiple functions of a virtualized evolved packet core in a single physical device or a group of adjacent devices. The analysis shows that the proposed grouping can reduce the network control traffic by 70 percent. <s> BIB001 </s> Softwarization of Mobile Network Functions towards Agile and Energy Efficient 5G Architectures: A Survey <s> Grouping EPC Functions. <s> With ever growing mobile Internet and the explosion of its applications, users are experiencing abundant services from different content providers via different network service providers in the heterogeneous network. The information-centric network (ICN) advocates getting rid of the current host-centric network protocol because information dissemination rather than end-to-end communication contributes to the majority of today's network traffic. Furthermore, it is better for network entities to converge as a whole in order to take advantage of open, scalable, and smart traffic transmission. The cloud radio access network is one of the emerging architecture evolutions on the wireless side for easier infrastructure deployment and network management. Therefore, when the information-centric network meets the C-RAN in the Het-Net, it is worthwhile and consequential to integrate ICN protocol with C-RAN architecture to achieve more efficient communication and information management. Moreover, SDN has been recognized as another promising architecture evolution to achieve the flexibility and reconfigurability of dense HetNets; its inherent advantage lies in global uniform control of the wired network. Thus, any of ICN, C-RAN and SDN is the complementary to the others. In this article, we contribute to a fresh proposal for and elaboration of the integration of the ICN, CRAN, and SDN for the HetNet to achieve a win-win situation. The vision of the proposed system is demonstrated, followed by the advantages and challenges. We further present a hybrid system in a large-scale wireless heterogeneous campus network. <s> BIB002
Virtualization in the EPC can be enabled by grouping the EPC network functional entities into different segments to attain less control, signaling traffic, and less congestion in the data plane BIB001 BIB002 . This can be achieved by integrating the PGW with the SGW and place them into a controller. In BIB001 BIB002 the MME is migrated with the home subscriber server (HSS) front-end (HSS-FE). The HSS-FE is an application that implements all the logical functionalities of the HSS but does not contain the user's information database. It requests the user information from the user-data repository (UDR, the central user information database) and stores these data temporarily in its cache memory. In this way, authentication and authorization are processed internally, without performing any data transmission through the network. The PGW and SGW are migrated into one virtual machine (VM) or into one virtual network function (VNF), to minimize the number of nodes involved in the data plane chain. Furthermore, the UDR, the online charging system (OCS), and the offline charging system (OFCS) are migrated into the PCRF. The idea behind this migration is that the PCRF requests user information in order to generate the required policies for each established bearer, and thus information exchange is minimized resulting in low latency for policy function generation. The two approaches that we describe next BIB002  both group some of the EPC functionalities, although in different ways. The SoftCell architecture in  involves disaggregation of the PGW, SGW, and MME functions and then partially implementing them in a distributed manner, as VNFs in the controller and switches. The PCRF and PCEF, usually implemented in the PGW, are grouped and implemented in the controller, while the packet classification is performed by the switches. The controller also performs the MME functions, in its traffic management layer. The data bearers assignment, usually performed by the SGW, is implemented by the controller in advance, as soon as the UE moves near a new BS. The architecture introduced in BIB002 adopts a "one plane grouping" strategy; that is, the EPC and Radio Access Network (RAN) entities are grouped into one common network plane, in the presence of controllers deployed in an upper plane. The network entities are virtualized and deployed in one plane to achieve efficient interworking, and such allows independent networks to be reconfigured in a flexible manner and automatically on the same physical infrastructure. These two architectures are discussed in greater detail next. The SoftCell architecture  consists of softwarized access switches that perform fine-grained packet classification on traffic from UEs located at the EPC network edge. Then, the controller computes and installs switching rules that realize a high level service policy, specified based on the subscriber's profile. In  , researchers try to provide flexible policies in the EPC without compromising scalability. To come up with an efficient EPC design, the factors affecting the EPC scalability were considered and publicly available network statistics were utilized. The EPC design consists of commodity middleboxes (e.g., transcoders, firewalls, and routers) and switches managed by a controller that supports flexible high level service policies. It computes and installs rules in the switches to direct traffic in both directions of a connection, thus minimizing the use of specialized network devices. The data traffic is then directed through a sequence of middleboxes optimized to the network conditions and UE locations, using the controller. In the data plane, hierarchical addressing (grouped by BS) and policy tags (identifying paths through middleboxes) are used in the EPC switches to forward traffic and the packet classification is pushed to the access switches, which are located at the EPC edge. There, fine-grained rules are specified by the controller and applied to map UE traffic into policy tags and hierarchical addresses. The SoftCell architecture leverages some properties of the EPC, that is, by considering that traffic begins at the network edge. In this way, each BS has a serving access switch (e.g., an open vSwitch [19] ), located at the edge of the EPC, that performs fine-grained packet classification, whereas the radio hardware in the BS is not modified: in fact, SoftCell only changes how the BS communicates with the EPC, providing softwarized EPC functional elements. The EPC architecture proposed in BIB002 uses SDN, splitting the network into three planes; (i) application plane, (ii) control plane, and (iii) forwarding plane. In the forwarding plane, the EPC coexists with the access network as all the control functions are moved into the control plane. By doing so, the forwarding plane consists of virtualized network devices that perform switching and packet forwarding, according to the SDN paradigm. To relieve the EPC from traffic load, NFV is exploited to instantiate network functionalities such as PGW in the access network, while SDN triggers path reconfiguration of data traffic. In addition, data caching Wireless Communications and Mobile Computing 5 strategies are exploited to minimize the traffic that goes through the EPC; that is, NFV techniques are used for caching popular content and store it on the EPC and access network when the network is idle, thus reducing the pressure in the data links and SDN controllers. In this way, latency can be minimized as content is cached locally, and better network management can be achieved through the use of virtualized EPC NFs. Discussion. The proposed architectures BIB002  differ from one another. In BIB002 , the networks, RAN and EPC, and the VNFs are in one plane whereas, in  , the distinction between RAN and EPC is maintained, with only the EPC entities being virtualized. However, both of them use an SDN controller for network management and policy enforcement, under different user mobility and traffic load variations. That is, the infrastructures are deployed with simplified and virtualized network devices, whose software is decoupled from the hardware and centralized to the control entity. Entities such as switches solely take the strategy developed by the controller and forward traffic to access networks. The architecture in BIB002 avails the potential of reducing latency through traffic offloading and caching in the RAN and EPC network. An advantage of  , is the ability to "mix and match" network devices from different vendors, which is also possible in BIB002 . The challenge in  is that the centralized controller may become a source of bottleneck for the network operation when the network scales up, due to the fact that all the control functionalities are pushed towards it. To reduce this burden, a wireless side of the network introducing the concept of Cloud-RAN (C-RAN) is proposed in BIB002 , where the base band unit (BBU) pool has both control and data forwarding functions, in addition to the controllers deployed in the control plane. The logically centralized BBU pool has the network wide view of the RAN and the EPC, yielding a seamless integration of the wired and wireless parts of the network. Through collaborative control, contents can be optimally distributed and stored in diverse devices of the EPC and the RAN via caching and broadcasting, thus overcoming the bottleneck problem of  . Energy Efficiency. The emergence of a network paradigm supporting social requirements is one of the aims of 5G. With softwarization, information centric networking (ICN), as one of the candidates, can be enabled where in-network caching can be provided. The content cache server caches contents passing through the node and then autonomously selects which contents to cache based on the need of the mobile users accessing the node, that is, based on the content request frequency. This approach can reduce the overall energy consumption within the network, since contents are cached and stored in close proximity to mobile users. In addition, in-network caching reduces the traffic (content transmission) within the network and also facilitates innetwork data processing  , whereby each network node carries out some data processing and service provisioning. This leaves some of the nodes within the network inactive, thus enabling energy saving procedures (e.g., switchingoff unused nodes). The proposed architecture in BIB002 can improve energy efficiency as it allows content caching in the EPC and the RAN, while  does not employ any energy efficient EPC procedures, except for implementing policies for data traffic directions, which can also make some of the middleboxes inactive.