What is SDN (Software-Defined Networking)?

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5G is coming and is bringing a range of new technologies to the table, including Software-Defined Networking. It is an essential element of 5G, and is a network development concept with a completely new infrastructure. Adlen Ksentini, a researcher at EURECOM, presents the inner workings of SDN.


How would you define SDN?

Adlen Ksentini: Software-Defined Networking (SDN) is a concept that was designed to “open up” the network, to make it programmable in order to manage its resources dynamically: on-demand routing, load distribution between equipment, intrusion detection, etc. It is an approach that allows network applications to be developed using a classic programming language, without worrying about how it will be deployed.

A central controller (or SDN controller) with overall control over the infrastructure will take care of this. This creates more innovation and productivity, but above all greater flexibility. SDN has evolved significantly in recent years to be integrated into programming networks such as 5G.

How does SDN “open up” the network?

AK: A network is arranged in the following way: there is a router, a kind of traffic agent for data packets, then a control plan that decides where those data packets go, and a transmission plan that transmits them.

The initial aim was to separate the control plan from the data flow plan in the equipment because each piece of equipment had its own configuration method. With SDN, router configuration is shared and obtained via an application above the SDN controller.  The application uses the functions offered by the SDN controller, and the SDN controller translates these functions into a configuration understood by the routers.  Communication between the SDN controller and the routers is done through a standardized protocol, such as OpenFlow.

How was the SDN developed?

AK:  The term first appeared about ten years ago and has been widely used ever since Cloud Computing became commonly used. “On-demand” networks were created, with virtual machines that then needed to be interconnected. This is the purpose of the SDN controller that will link these virtual machines together, translating information coming from different services. The concept has evolved and become a core technology, making it possible to virtualize infrastructure.

Why is it an essential part of 5G?

AK: 5G is intended for use in different markets. For example, Industry 4.0 or augmented reality require a variety of network services. Industry 4.0 will require very low latency, while augmented reality will focus on high bandwidth. To manage these different types of services, 5G will use the concept of network slicing.

This consists in virtualizing a structure in order to share it.  SDN is the key to interconnecting them, as it creates the ability to allocate network resources on demand. Thanks to this flexibility, it is possible to create specific network slices for each use. This is the principle of core network virtualization that is fundamental to 5G.

How does this principle of “resources on demand” work?

AK:  Imagine a company that does not have enough resources to invest in hardware. They will rent a virtual network: a cloud service offered for example by Amazon, requesting resources defined according to their needs. It could be a laboratory that wants to run simulations but does not have the computing capacity. They would use a cloud operator who will run these simulations for them. Storage capacity, computing power, bandwidth, or latency are thus configured to best meet the needs of the company or laboratory.

Why do we talk about new infrastructure with the SDN?

AK: The shift from 3G to 4G was an improvement in throughput or bandwidth, but was basically the same thing. 5G, with SDN, has a better infrastructure through this virtualization and can not only capture classic mobile phone users, but also open the market to industries.

SDN offers unique flexibility to develop innovative services and open the networks to new uses, such as autonomous vehicles, e-health, industry 4.0, or augmented reality. All these services have special needs and we need a network that can connect all these resources, which will certainly be virtual.

Tiphaine Claveau for I’MTech

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