Software Networks, 2nd Edition

2SDN (Software-Defined Networking)

The SDN (Software-Defined Networking) technology is at the heart of this book. It was introduced with strong control centralization and virtualization, enabling physical networking devices to be transformed into software. Associated with this definition, a new architecture has been defined: it decouples the data level from the control level. Up until now, forwarding tables have been computed in a distributed manner by each router or switch. In the new architecture, the computations for optimal control are performed by a different device, called the controller. Generally, the controller is centralized, but it could perfectly well be distributed. Before taking a closer look at this architecture, let us examine the reasons for this new paradigm.

The limitations of traditional architectures are becoming significant: at present, modern networks no longer optimize the costs at all (i.e. the CAPEX and OPEX). The networks are not agile. The time to market is much too long, and the provisioning techniques are not fast enough. In addition, the networks are completely unconnected to the services. The following points need to be taken into account in the new SDN paradigm:

• – overall needs analysis;
• – dynamic, rather than static, configuration;
• – dynamic, rather than static, policies used;
• – much greater information feedback than is the case at present;
• – precise knowledge of the client and of his/her applications, and, more generally, his/her requirements. ...