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There is no denying that Software Defined Networking (SDN) will radically change the networking landscape, but SDN is not a one-size-fits-all proposition. Considerable differences exist between various types of networks and domains, including data centre and service provider WANs, all of which will be impacted by SDN.

CONTEXT SPECIFIC
Firstly, one needs to understand the distinct use cases in different network domains. Each will require different views of the control and application layers in the SDN architecture.

For data centre and enterprise networking, SDN rollouts will concentrate on delivering seamless public, private and hybrid cloud environments, by integrating virtualised computing, storage and connectivity environments. The rollout will entail the virtualisation of WAN bandwidth for efficiency and facilitate multi-vendor networks for accelerated deployment and management of new applications requiring carrier grade WAN connectivity. This virtualised network reduces the time to enable new capabilities and scalability and enhances customisation of network forwarding behaviour, improving security and differentiation.

For service providers it's a different picture. They work with multi-layer networks, such as packet and transport (optical circuits and/or wavelengths) and multiple network domains spanning broad geography. These networks support several service frameworks and types and are forever evolving as service providers pursue new revenues, as well as serving many customers on each service. The provider can only control customer behaviours through policy and pricing.

The service provider WAN equipment layer is relatively complex, comprising numerous, evolving networks and domains spanning multiple network layers. This in turn suggests a complicated and expansive control layer. Logically, the control layer assumes complete responsibility for path and flow, connection control and management, thus freeing the application layer from this responsibility.

OPENNESS
Complexities faced by service providers establish the need for southbound (from the control layer) openness. After all, the primary imperative of SDN is to unleash productivity and innovation, making network behaviours software defined. For these properties to be fully exploited, openness is critical. There is no point in adopting software that's as closed and locked as today's hardware-based systems, denying the innovations and agility that SDN promises.

This innovation is only possible if service providers innovate within the control layer. Absolute openness between the control and equipment layers is mandatory. Without such openness the control and equipment layers cannot be changed independently of each other. Software driven networking paradigms which glue control layer systems to physical networks neglect this point when positioned as final-form architectures, prioritising vendor interests over those of service providers.

UNLOCKING INNOVATION
The advantages of a multi-layer SDN powered network are numerous. However, the ability to control network behaviour across, rather than simply within network layers is a major advantage. Consequently, services can be transported over the most efficient technology and not over predefined or existing transport technology.

For most networks the ability to alleviate congestion by obtaining bandwidth from a lower layer takes days, weeks or months as the administrators for each layer negotiate and execute the capacity request. Intelligent multi-layer SDN can free the network and its operations team from this work and make the best path determination - weighing layer trade-offs - in milliseconds.

Multi-layer SDN powered networks can also eliminate the need for hold-down timers. Instead, the SDN controller will simply address the failure immediately at the most appropriate layer, resulting in shorter downtimes.

With the inexhaustible processing power of cloud computing, taking openness, interoperability and an understanding of the differences between various types of networks into consideration, you can create a successful SDN-powered network. Service providers and enterprises can reap the rewards of a network that uses between 15 to 60 per cent less bandwidth, reduces operational expenses through intelligent automation, and supports the delivery of new services with far greater agility. NC