Software-Defined Networking (SDN) is an emerging paradigm that separates the network’s control logic from the underlying routers and switches, enabling centralization of network control, and presenting the ability to program the network. SDN makes it easier to create and introduce new abstractions in networking, simplifying network management and facilitating network evolution
An important concept in Software Defined Networking is orchestration, known either as SDN orchestration. It presents the ability of the network to have automated behaviors to manage and coordinate the hardware of the network and software elements to support services and applications.
SDN implements a level of orchestration to have a more flexible and les complex network compared to the traditional ones.By implementing a new orchestration level, SDN can tackle the inflexibility and complexity of the traditional network. SDN provides enterprises with the ability to control their networks programmatically and to scale them without affecting performance, reliability, or the user experience. The interfaces are programmable and replace the distributed nodes with control functions to have a quicker adjust network configurations and to create new services.
Figure 1. SDN Architecture
There are several ways how SDN orchestration can work. One of the examples is manual job that is generated with service orders made by a customer. Another way is using a website where the customers can also order. In these cases, to provision the service it is required the usage of SDN orchestration technology. Virtual network layers, security services or server-based virtualization or required to be set up. There are policy rules, which, combined with service orders and the status of resources that are available, determines the location of the functions that make up the service as well as connections between them.
The functionalities can be divided in two categories:
- Service orchestration; one example for this is the VPN setup among several sites or delivering a specific set of firewall and IPS/IDS service options to a customer
- Infrastructure orchestration; which includes Open Stack usage for switches, servers or storage.
It is expected a great future for SDN orchestration as it tends to go toward a cloud-based network which include many new and existing technologies and communication services. Most of new technologies try to provide coordination and automation of network for better performance between data center and telecom systems. Now it is developing a new concept about network, Network as a Service (Naas) in cloud platforms.
There are four services offered by the controller for SDN orchestration:
- Provisioning, it provides all the basic features of the connection between two locations, which are the setup, tear down and the modification.
- Topology Discovery, its role is to export the information of the topology with identifiers that are unique. But it also does some computation for the path of different scenarios.
- Monitoring, the network has to have a “back up plan” in case of failures in order to request other connection.
- Global Path Computation, connection in the end host will be optimized if the path computation is done in a global view of the connection.
 W. Arnold, D. Arroyo, W. Segmuller, M. Spreitzer, M. Steinder, and A.Tantawi, “Workload orchestration and optimization for software defined environments,” IBM Journal of Research and Development, vol. 58, no. 2, pp. 1–12, March 2014
 Networking: Implementation Prospects and Challenges. IEEE Network Operations and Management Symposium (NOMS) 2014
 Lombardo A, Manzalini AG, Riccobene V, Schembra G. An Analytical Tool for Performance Evaluation of Software Defined NetworkingServices. IEEE Network Operations and Management Symposium (NOMS) 2014
 Aryan TaheriMonfared and ChunmingRong. “Flexible Building Blocks for Software Defined Network Function Virtualization.” In: 2014 IEEE 10th International Conference on Quality, Reliability, Security and Robustness in Heterogeneous Networks (QShine). IEEE .2014
 W. John, A. Devlic, Z. Ding, D. Jocha, A. Kern, M. Kind, A. Kopsel, ¨V. Nordell, S. Sharma, P. Skoldstr ¨ om, D. Staessens, A. Takacs, S.Topp, ¨ F.-J. Westphal, H. Woesner, and A. Gladisch, “Split Architecture for Large Scale Wide Area Networks,” ArXiv e-prints, Feb. 2014