The emergency relating to software-defined networking (SDN), especially in terms of the prototype associated with OpenFlow, provides new possibilities for innovating on network design. Researchers have started to extend SDN to cellular networks. Such new programmable architecture is beneficial to the evolution of mobile networks and allows operators to provide better services. The typical cellular network comprises radio access network (RAN) and core network (CN); hence, the technique roadmap diverges in two ways. In this paper, we investigate SoftRAN, the latest SDN solution for RAN, and SoftCell and MobileFlow, the latest solutions for CN. We also define a series of control functions for CROWD. Unlike in the other literature, we emphasize only softwaredefined cellular network solutions and specifications in order to provide possible research directions.

Software - defined networking (SDN) is a promising technology for next-generation networking and has attracted much attention from academics, network equipment manufacturer, network operators, and service providers. It has found applications in mobile, data center, and enterprise networks. The SDN architecture has a centralized, programmable control plane that is separate from the data plane. SDN also provides the ability to control and manage virtualized resources and networks without requiring new hardware technologies. This is a major shift in networking technologies.
The ITU-T has been engaged in SDN standardization, and the European Telecommunications Standard Institute (ETSI) has been working on network function virtualization (NFV), which complements SDN. The Open Network Foundation (ONF) is a non-profit organization dedicated to promoting the adoption of open SDN. Recently, much work has been done on SDN to meet future network requirements.
Network virtualization creates multiple virtual infrastructures within a deployed infrastructure. These virtualized infrastructures can be created over a single physical infrastructure. Each virtual network can be isolated from each other and programmed to meet user requirements in terms of resource functionality and capacity. This ensures that appropriate network resources are provided to the user.
The SDN framework includes programmable control plane, data-forwarding plane abstraction, and methods to map the virtualized infrastructures onto the underlying physical network infrastructure.
Key issues to be addressed are network resource isolation, network abstraction, topology awareness, quick reconfigurability, performance, programmability, management, mobility, security, and wireless network access.
We received strong response to this call for papers on SDN from network operators, equipment manufacturers, universities, and research institutes. Following a peer-review process, we selected nine papers for inclusion in this special issue.
The first paper,“Network Function Virtualization Technology: Progess and Standardization”discusses the main challenges in SDN faced by network carriers. This paper also discusses current standardization activities and research on NFV related to SDN.
The second paper,“Service Parameter Exposure and Dynamic Service Negotiation in SDN Environments,”discusses the ability of SDN to facilitate dynamic provisioning of network services. The paper focuses on two main aspects of the SDN framework: network abstraction and dynamic parameter exposure and negotiation.
The third paper,“SDN-Based Broadband Network for Cloud Services,”discusses how SDN/NFV will be vital for constructing cloud-oriented broadband infrastructure, especially within data center networks and for interconnecting between data center networks. The authors propose SDN/NFV in broadband access to realize a virtualized residential gateway.
The fourth paper,“D-ZENIC: A Scalable Distributed SDN Controller Architecture,”describes a solution to minimizing the cost of network state distribution. This solution is a network control platform called D-ZNEIC that supports distributed deployment and linear scale-out by trading off complexity for scalability.
The fifth paper,“Software-Defined Cellular Mobile Network Solutions,”describes current research on and solutions for software-defined cellular networks. It also discusses related specifications and possible research directions.
The sixth paper,“SDN-Based Data Offloading for 5G Mobile Networks,”describes an integrated 4G/Wi-Fi architecture evolved with SDN abstraction in the mobile backhaul and enhanced components that facilitate the move towards 5G.
The seventh paper,“Integrating IPsec Within OpenFlow Architecture for Secure Group Communication,”discusses Internet Protocol security (IPsec) in the context of OpenFlow architecture and SDN.
The eighth paper,“Virtualized Wireless SDNs: Modelling Delay Through the Use of Stochastic Network Calculus,”describes a delay model for a software-defined wireless virtual network with some theoretical investigation into wireless SDN.
The final paper,“Load Balancing Fat-Tree on Long-Lived Flows: Avoiding Congestions in Data Center Network,”describes a dynamic load-balancing algorithm for fat tree in the context of SDN architecture.