Network Function Virtualization and Service Function Chaining Frameworks: A Comprehensive Review of Requirements, Objectives, Implementations, and Open Research Challenges  
School of Computing Science, University of Glasgow, Glasgow G12 8 QQ, UK; [EMAIL_ADDRESS]  
School of Computing Science, University of Glasgow, Glasgow G12 8 QQ, UK; [EMAIL_ADDRESS]  
School of Computing Science, University of Glasgow, Glasgow G12 8 QQ, UK; [EMAIL_ADDRESS]  
School of Computing Science, University of Glasgow, Glasgow G12 8 QQ, UK; [EMAIL_ADDRESS]  
School of Computing Science, University of Glasgow, Glasgow G12 8 QQ, UK; [EMAIL_ADDRESS]  
School of Computing Science, University of Glasgow G12 8 QQ, UK; dimitrios.pezaros@glasgow. using a centralised network controller that has a _global_ logical view of the entire network infrastructure, and handles tasks such as the creation of service chains and orchestration of traffic between vNFs [8]. In terms of the location of network functions in a service chain, the virtualized infrastructure can span multiple datacentres, which calls for inter-data-centre networking or within the same data centre, which results in an intra-data-centre network (see Section 2.2). We generally expect the SFCs to be adaptive and dynamic; service chains should have the feature of readjusting to the unpredictable nature of service requests, and to offer better quality of service (QoS) for the end user [9; 10]. If we consider network security as an example, such a service may consist of network functions such as firewalls, deep packet inspection (DPI), intrusion prevention or detection modules installed as software, which are chained together [11]. Several implementation frameworks have been proposed in the literature, some of which have been adopted and deployed at a commercial scale, while others are in the experimental state of development. In this paper, we put together these frameworks while highlighting their contributions and how they solve research problems associated with realising NFV/SFC in service provider network environments. Experts from both academia and industry are putting a lot of effort in the research and development of SFC. While NFV/SFC has developed over the years, developments in this domain are so substantial that it makes a survey now quite different and valuable from a (hypothetical) survey put together a few years ago. Unlike previous surveys in this area, our work (layout in Figure 1) also shows how SDN, NFV, and SFC are combined in the provisioning, operations, and management of next-generation networks. We further explain how our work differs from previous efforts by presenting related surveys in Section 2; thus, our contributions are threefold:  
* We present the vNF chaining requirements (Section 2.1) and how they relate to SFC implementations in service provider networks, thus some use cases for the SFC paradigm (Section 2.2) are presented. An overview of the current state-of-the-art SDN, NFV, and SFC (Section 3) is also presented as the foundation for the frameworks reviewed in this paper;
* We present a comprehensive survey of the state-of-the-art NFV frameworks for building and implementing vNFs, particularly frameworks that have been proposed for use in SFC environments. We also present a taxonomy of SFC implementation frameworks, focusing on each SFC-related challenge, each one addressing the approaches used (Section 4);  
Figure 1: High-level paper structure. Finally, we identify and discuss the main open research challenges associated with NFV and SFC environments in the next generation networks (Section 5). The remainder of this paper is structured as follows: Section 2 presents the background and motivation of this survey, considering what has been done in the literature and highlighting the uniqueness of our approach and reflections on the state of the art approaches. Section 3 briefly discusses the underlying technological advancements that make NFV possible.