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Global network infrastructure is driving unprecedented bandwidth demand across all segments, including access, metro, regional, long haul and submarine. Fuelling this is the adoption of smartphones, video-centric applications and cloud-based business services. While global network operators struggle to cost-effectively handle this growth, a more challenging dynamic has emerged: the move to dynamic network connectivity, when and where it is required.

There is a consensus that networks traditionally connecting users-to-content and content-to-content will move from static to on-demand connectivity. But is underlying network infrastructure ready and if not, must it be entirely replaced - or is a more elegant and cost-effective migration path possible?

Numerous discussions and debates around Software Defined Networking (SDN) and Network Functions Virtualisation (NFV) are producing a new networking paradigm that will radically change how networks are designed, deployed and operated, offering increased business agility, lower costs and shorter software innovation cycles. Once again, the suitability of existing underlying networks must be considered.

SDN-enabled networks separate the Control Plane from the Data Plane, and some if not most software currently running on network devices must be ported to upper layers. A software-based SDN controller resides between the applications and underlying infrastructure layer and abstracts the latter into a programmable domain of connectivity resources. New software-based assets including enhanced applications can directly express their needs to the underlying network and SDN controllers and both run on local or cloud-based platforms. Upgrading the infrastructure layer will be network operator dependent since each infrastructure and operational model is unique.

Certain network elements are more appropriate to an SDN-based architecture than others. Routers and switches migrate more easily to white box or bare metal platforms with minimal embedded software, since control plane functions are implemented at upper layers. However, certain functionality is far better implemented at the infrastructure layer, such as real-time packet OAM (Operations, Administration, and Maintenance), latency measurements, signalling and discovery, and some software is still required within devices operating in the infrastructure layer. Application Programming Interfaces (API) abstract the underlying infrastructure layer from the upper control layer which is mostly implemented using software upgrades to in-service network devices, avoiding outright hardware replacement.

Deploying standards-based APIs using software upgrades to existing hardware means that operators can combine different network elements from different hardware vendors into a seamless pool of network connectivity. Legacy platforms that cannot be upgraded to support standardised APIs will have to be replaced.

Consumed content is only valuable if it can move to and from data centres, meaning that it ultimately travels across the photonic layer, comprised of optical fibre, coherent modems, ROADMs and amplifiers. This layer is the least standardised and operates within the more difficult analogue domain. Most associated functionality cannot be virtualised, but is nonetheless compatible with SDN architectures using open standardised APIs to abstract and hide underlying complexity. Because most photonic networks implement DSP technology with coherent optical processors, some functionality could possibly be ported to the application layer, but this is unlikely as it is best served within the network.

Should network operators upgrade their entire network to reap the SDN benefits? A resounding no. New software-based applications and SDN controllers are required, but most existing network infrastructure can be software upgraded. Where legacy hardware platforms are upgraded for other reasons, such as energy efficiency or obsolescence, operators should consider open programmable hardware platforms that integrate packet switching and coherent optics into a single device to simplify network designs, deployments, and operations. Each operator has unique network and operational practices, meaning that their infrastructure layer migration path to an agile SDN-based network is also unique. That said the end game is the same - delivering increased agility, rapid service innovation and cost-effectiveness. NC