4. Conclusion

In 2017, the technologies implemented in SDN architectures are very diverse and linked to specific use cases. It remains complicated to have an SDN controller that can manage all use cases. What's more, from an architectural point of view, this could also be a nonsense, as it could lead to problems of scaling, QoS management, etc. Indeed, the whole complexity of introducing central controllers will be to find the balance between functions to be centralized and functions to be distributed (as well as finding the right level of distribution). This balance will depend on each network and the associated services and constraints. The solutions on the market are diverse and non-interoperable today, although they are often based on certain standard protocol bricks. Their scope is also very varied, ranging from simple controllers with no real intelligence, to targeted applications (service chaining,...