The modern communication networks have evolved from simple-static systems to highly flexible and adaptive systems facilitating dynamic programmability and reconfiguration. This network evolution has influenced the lowest level of packet processing in data plane to highest level of network control and management functions. It has also influenced the overall network design and architecture which is clearly evident from the emergence of SDN and NFV. With the wide-spread acceptance of SDN, a novel networking paradigm, the network programmability has re-appeared as a top research area in networking and numerous programming languages have been proposed. In this paper, we present a systematic review of various state-of-the-art SDN programming languages used to program different network planes. We follow a top-down approach, starting with the high-level or top-tier programming languages followed by the data plane or bottom-tier programming languages. We have provided an in-depth analysis of various top-tier and bottom-tier programming languages and compared them in terms of most prominent features and supported abstractions. In addition to it, we have elaborated various programming models used in different bottom-tier programming languages which provide necessary abstractions for mapping diverse functionalities of data plane algorithms splendidly onto the specialized hardware like ASICs. Lastly, we have highlighted the research challenges in SDN programming languages like cross platform programming, necessary language libraries, support for network verification, NFV, stateful and inline packet processing, which need to be incorporated into existing programming languages to support diverse functions required in next generation networks.

The ever-increasing demands of Internet services like video on demand, big data applications, IoE and multi-tenant data centers have compelled the network industry to change its conventional non-evolving network architecture. Software Defined Network (SDN) has emerged as a promising network architecture which provides necessary abstractions and novel APIs to facilitate network innovations and simplifies network resource management by breaking the conventional network into multiple planes. All these SDN planes interact through open interfaces or APIs which are commonly categorized into southbound, northbound and west/eastbound interfaces. In this manuscript, we have identified and emphasized various communication protocols used at south and northbound interfaces. We have provided a taxonomy of south and northbound communication protocols based on their dependence, capabilities and properties. The pros and cons associated with each communication mechanism are highlighted and the numerous research challenges and open issues involved at these two interfaces are elucidated. In addition to it, we have proposed the necessary abstractions and extensions required in communication protocols at these two interfaces to simplify real-time monitoring and virtualization in next generation networks.