Guest Editorial (2015)

The number of devices connected, as well as the amount of traffic in the network has increased exponentially in the last years. Moreover, the emergence and maturity of new services and use cases such as mobility, server virtualisation, cloud computing and Internet of Things have been driven, and somehow restricted, by the limitations of actual network architectures.Software Defined Networking (SDN) is a new way of thinking about the networks. The basic idea of SDN is the separation between data and control plane in network devices and the centralised control of the network. This paradigm makes easy the development of new services and applications and also reduces the complexity of network configuration and management [1]. This new global view of network resources has led to tremendous advances in intelligent network services, usually not fulfilled by traditional architectures. In fact, SDN has fostered new concepts in networks such as Network Operating Systems (NOS), High Level Network Operating Languages and Network Function Virtualisation (NFV) [2, 3]. Nevertheless, there are many issues and challenges related to the standardisation of SDN interfaces, orchestration and efficient resources management; SDN multi-platform convergence; advances in Southbound and Northbound APIs; the market expectation of the combination of SDN and NFV [4]; co-existence and integration of SDN with traditional architectures; security, privacy, authentication, trust and verification with the SDN technology; quality of service, among others [5]. SDN has the potential to program the network behaviour and, in this way, enhance the quality of the services of stakeholders. This Special Issue reflects the research and application of Software Defined Network in the following fields: high level protocols, mechanism or advances to combine and enable SDN and NFV, performance analysis on single- and multi-controller architectures, virtualisation and cloud computing environments, testing and security analysis and experiences in the deploying of new SDN applications and services. D. Vicino et al. analysed the behaviour of the BitTorrent protocol deployed in SDN networks and their performance in case of topology changes. For this purpose, the authors use 32 switches connected in a ring topology, using Mininet simulator and NOX controller. Each switch is connected to a single BitTorrent client and the bandwidth in their network interface is limited. The controller regularly changes the topology, removing one link of the ring in a round robin mechanism. The results of this work show the effects in the propagation rate in comparison with traditional experimentation. This information is obtained from a previous work deployed in PlanetLab, which emulates the same topology using HTTP protocol. This work opens new challenges related to the use of high-level protocols like BitTorrent to avoid negative effects in the network performance. L. I. Barona et al. presented an analysis of the trends on virtualisation using two promising technologies: SDN and NFV. On one hand, SDN allows the programmability of the network by means of an external entity, which has a complete view of the network. On the other hand, NFV changes the traditional Network Functions (NF) like firewalls or load balancers toward a virtual environment where the virtual NF can be deployed easily and in less time. These technologies are complementary to each other, and aim towards the enhancement of management, rapid deployment and control of the network devices. In this paper, the authors shows a survey of these technologies, analysing the current research, challenges and the possible benefits of combined SDN and NFV. A. Stanik et al. proposed an architecture called ProgNET that enables QoS guarantees in the orchestration and federation in cloud environments (between virtual machines in a single data centre and among different clouds). The authors present the initial approach based on SDN concept in order to provide additional services to the customers with enhanced quality by means of a dynamic Service Level Agreement (SLA) protocol. The paper proposes the combination of OpenFlow with WS-Agreement standard and WS-Agreement Negotiation to define the requirements of the service providers. The architecture is composed for three layers: the Front-End, which allows the communication with the customer through a GUI; the SLA Manager layer is in charge of the SLA negotiation process; the third layer is known as Network Manager, and allows the allocation of the resources. Lingxia Liao et al. proposed a distributed FlowVisor (DFVisor) platform to enhance the virtualisation capabilities of FlowVisor in SDN Networks. FlowVisor allows the virtualisation of the network, however, it has scalability concerns. In this context, DFVisor introduced a layered overlay mechanism and a distributed synchronised database in order to enhance network, addressing space and switch capacity. The main contributions of this paper are: i) allow fine-grained QoS requirements, ii) enable advanced push-based flow setup and statistics collection mechanism and iii) the use of a distributed synchroniser two level database in order to centralise the network configuration and facilitate the synchronisation of the data, flows and statistics. This model is implemented using NOX, Apache Zookeeper and enhanced OpenFlow switch based on CPqD. Finally, the authors present the main issues of the platform, based on the evaluation of flow setup and the statistics gathered. Kashif Mahmood et al. presented a model for the analysis of the OpenFlow performance. For this purpose, the authors used Jackson network to model the data plane and M/M/1 queue to the control plane (controller) in SDN networks. The novelty of this paper is that it introduces the multiple node case and allows the evaluation and the dimensioning of the network level. Some assumption are considered in the model design: i) the network of queues has reached steady state, ii) arrivals in different nodes and their respective service times are independent of each other and iii) arrival processes and services times are considered to be a Poisson processes. The author also considered two cases: infinite buffer at the controller (there aren't dropped packets) and finite capacity of the controller (the buffer space of the controller is limited to X spaces). The performance evaluation is done with three nodes connected in serial way, the outside traffic are connected to node 1 and 2. The authors provided a probability density function (PDF) and cumulative density function (CDF) of the time spent by the packet for a specific path in SDN network.