SDN: Software Defined Networking & Networks

SDN Software Defined Networking Includes:
SDN basics     SDN OpenFlow    

Software defined networking, SDN is a telecommunications network architecture that provides the promise of significant improvements in the network performance.

Using software defined networks the is possible to make the network more dynamic, manageable, cost-effective, and adaptable.

The key behind software defined networking is that the SDN architectures decouple network control and forwarding functions. This enables the network control to become directly programmable. As a result the underlying network infrastructure can be abstracted from applications and network services.

As greater levels of efficiency are required along with greater flexibility to meet the changing demands over time as a result of different usage patterns each day, week and with special events and the like, it is necessary to utilise all the elements within the data network as effectively as possible.

Software defined networking enables resources to be configured to meet the functions needed at any given time and to ensure that traffic is able to flow in the best manner possible at all times.

Software defined networking background

The huge growth in mobile devices and the data they use along with server virtualisation and the use of cloud services as well as many other changes have caused many in the telecommunications industry to re-examine the network architectures that have been used for many years.

Many of these networks are tiered and have a very hierarchical structure with many Ethernet switches arranged in a tree structure.

This form of static telecommunications network design topology made much sense when client serving computing was the main method of working. However this form of network architecture is ill suited to the dynamic computing and storage needs that have evolved around new computer usage scenarios with data centres, carrier environment and campuses.

Today, the traffic patterns in data networks have significantly changed. Often today's applications access a variety of different sources and servers and this creates a flurry of activity of data requests from a variety of different sources.

In addition to this, users are changing the way they work and this also has a major impact on the data network traffic. Often users will want to access data from a variety of physical locations, not just accessing the data from the office. As data requests often travel via a VPN, and from different areas of the globe, this is a far cry from the requests that some years ago tended to be from one machine to another in defined locations.

Cloud services are yet another driver for the use of software defined networking. Enterprises often need to access IT resources on demand. They do not want to have their own fixed set of assets they need to increases to meet the demand peaks. Instead it makes sense to have a common cloud resource provided by a third party that can act to average out the peaks and troughs of a number of different enterprises and still being able to provide additional resource as required. As might be imagined, this results in more data flow across the networks in a variety of different directions.

To meet these needs and others, a far more flexible and agile data network architecture is needed.

Software defined networking definition

As software defined networks can mean many things to different people, it is worth having a definition to refer to and understand exactly what software defined networking and networks are.

The software defined networking definition enables a concise top level picture to be gained of what the term really means.

Software defined networking concepts

With software providing a means by which much functionality can be provided, its adoption into networking enables many features to be run using software rather than hardware.

Some of the key concepts that are embedded in software defined networking include:

• Forwarding and control functions separated:   By separating these functions it is possible to control the forwarding side of the network to meet the changing traffic flow requirements.
• Programmable:   Not only is the network programmable, but the network control can be directly programmed because the control is decoupled from the forwarding functions.
• Central management:   One of the key concepts of software defined networking is that the network is controllable and software defined. This can only be achieved if the management is achieved using a central management core.
• Programmatic configuration:   software defined networking enables managers to configure, manage, secure, and optimize network resources. This can be achieved very quickly using automated programmes which monitor the network performance and implement the changes needed. In this way the data network can meet the ever changing demands placed upon it.
• Open standards usage:   One of the key requirements for software defined networking is that open standards are used. With data networks typically using network components from a variety of vendors it is essential that all these elements can operate together. This can only be achieved if common open standards are used. If open standards were not used, there would be a host of different vendor specific interfaces that would not operate together. One of the key open standards used within software defined networks is the Openflow standard.

Using software defined networking, the network control is detached from the elements of the network that providing the data forwarding.

Software defined network technology

The key technique used within software defined networking is to structure the network architecture so that the application layer, control layer and the infrastructure layers are separated and individually definable. The traditional approach had used a large number of devices that tightly bound together making it difficult access functions rather than complete devices.

This new approach strategy for software defined networks enables operators to gain control over the entire network from a single point. This greatly simplifies the data network design and operation.

This approach also simplifies the devices used because they no longer need to interface to and process very many different protocol standards, but instead they just need to accept instructions from the software defined network, SDN controllers.

The diagram below shows a logical view of software defined networking architecture with the three layers: application layer; control layer; infrastructure layer.

The intelligence for the network is typically contained within software defined networking controllers which are able to control the complete network. In this way, the whole network can be treated by the applications and policy entities as a single large logical switch.

By adopting this software defined networking approach, the whole network can be controlled from a single point. This greatly simplifies the design, operation and updates. SDN also simplifies the network devices themselves as they only need to interface with a single control standard and not the many protocol standards they would otherwise need to process.

Open Networking Foundation & SDN

The Open Networking Foundation, ONF is an industry organisation that has been set up with the aim of promoting and adoption of Software Defined Networking through open standards development.

The ONF draws its members from industry and coordinates the activities of software defined networking standardisation. It has developed the OpenFlow protocol which structures the communication between the control planes and data planes of a software defined network.

The OpenFlow protocol is widely used for software defined networks because it provides a common interface allowing operators successfully use different network elements from different providers knowing that they will interoperate successfully.

Difference between SDN & NFV

Software defined networking and network functions virtualization are very closely linked as they both have software as the key, but they are not the same.

The two techniques can be used together or separately. The main points of each are summarised below so that both SDN and NFV can be evaluated with their similarities and differences.

• SDN, Software Defined Networks:   SDN separates the network control and forwarding planes and provides a central view for more efficient implementation and running of the network services.
• NFV, Network Functions Virtualisation:   NFV focuses on optimising the network services themselves. This technique decouples the network functions from proprietary hardware, placing them on more generic servers or computers so these functions can run in software to provide more flexibility for operation, changes and updates.
  Read more about . . . . Network Functions Virtualization, NFV.
  
  

Although the two are similar the difference between SDN and NFV means that they are not the same. However both techniques can be used on the same network to provide significant benefits.

Software defined networks are now well established. As the efficiency of data networks needs to improve as costs per bit fall, SDN provides one path by which the effectiveness of networks can image more adaptable, dynamic, and manageable, whilst providing significant improvements in terms of their cost effectiveness.

  Written by Ian Poole .
  Experienced electronics engineer and author.

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