By Stu Benington
The evolving connectivity needs of businesses and consumers are day by day creating mounting pressures on service providers' traditional business models and further exposing the limitations of traditionally static transport architectures. These needs include ever-increasing demand for network capacity to satisfy bandwidth-intensive end-user applications, increasingly unpredictable traffic patterns and usage spikes, and, equally important, the transformational architecture shift toward a cloud-centric networking environment.
Today, all end-user services and applications are becoming either attached to the cloud or hosted in the cloud. Traversing both data centers and telecom central offices, which are in many ways evolving into data centers themselves, these cloud-centric applications and services are driving new workloads on the network. At the same time, these changes have unleashed a dynamic ecosystem with new entrants, new services, and the abstraction of applications from the network. The traditional value chain is being disrupted and competition for the market's profit pool is intensifying, creating further challenges for telecom service providers.
To meet these challenges, service providers in developed and emerging markets are turning to one of the industry's most promising technologies -- software-defined networking (SDN). While still in a formative stage from an implementation perspective in the wide-area network (compared to server and storage virtualization in the data center), SDN will play a critical role in enabling service providers to create a more efficient, agile, and scalable transport infrastructure capable of meeting the demands of cloud-centric connectivity.
While service providers have been exploring these concepts for a number of years, 2014 marks an important milestone for the technology as more and more operators make the move from research and lab trials to field trials in their networks. This trend was validated with the results of a recent Infonetics carrier survey in which 29% of participants responded that they are currently implementing SDNs and 52% indicated that they plan to evaluate SDNs by the end of 2014.
On-demand elasticity for a new networked world
As end users shift toward a cloud-centric world and traffic patterns in the wide area become more unpredictable, service-provider networks need to mirror the on-demand flexibility, scalability, and programmability of data-center compute and storage resources. The implication for multilayer, multivendor transport networks is profound. The requirement is not just to make the network more efficient; it's to fundamentally change the network paradigm and create an application-centric service delivery model capable of on-demand agility, flexible performance parameters, and seamless scalability. This need is compounded by the emergence of technologies such as network functions virtualization (NFV) that enable applications and network appliances to be distributed closer to the end user and leverage commercial off-the-shelf hardware.
Ultimately, the software-defined end-to-end transport network must not only serve, but also empower end-user applications (see Figure 1). This vision demands a very different way of looking at and administering the network. If done right, however, SDN implementation represents an opportunity for service providers to innovate in ways not possible before, while fully leveraging the value of existing assets, including their network resources, networking expertise, and investments in the network brand.
SDN and service transformation
As service providers transform existing network resources and architectures to compete in this new networked world, there are a number of key network attributes that need to be addressed. SDN technologies will play a critical role in each.
- Programmability. The fastest way to introduce and change services is to make the network more programmable -- in other words, make it fully adaptable to the changing needs of end users, network operators, and the applications themselves. Software-defined programmability and automation of network resources will enable service providers to unlock new service revenue opportunities (e.g., transport as a service, bandwidth-on-demand, scheduled bandwidth, etc.), adapt to real time network changes (e.g., virtual machine migration), reduce overall network complexity, and more efficiently use network resources at the lowest cost.
- End-to-end multilayer integration. As end-user services and applications increasingly move to private and public cloud networks, the need for agile and efficient integration of compute and storage resources across multiple geographies (e.g., access, metro, core) and protocol layers (e.g., wavelength, Optical Transport Network, Ethernet, IP/MPLS) becomes increasingly important. SDN can play an important role in harmonizing capabilities across this broad range of resources and enabling a true end-to-end global view of the network. Of particular importance is optical layer flexibility. The physical layer of the network has witnessed significant technology advances, including coherent transmission, colorless/directionless/contentionless ROADMs, flexible-grid-enabled superchannels, and photonic mesh. For maximum flexibility, scalability, and resiliency, service-provider transport networks must fully leverage such technology innovation at the photonic layer to meet the performance requirements of cloud-centric residential and enterprise applications. That can only be fully realized with SDN through inclusion of the optical layer as a legitimate alternative to pure packet forwarding as application needs dictate.
- Openness. Packet optical transport infrastructure networks by nature are multivendor and multitechnology and therefore depend on standards-based protocols to enable interoperability at the physical layer. SDN enables an unparalleled ability to administer multivendor networks and architectures with an open and collaborative software-based development process focused on end-user applications and optimized for enhanced-network prorammability. An open SDN environment has huge potential for both users and operators. It can drive innovation at an unprecedented pace by enabling the easy introduction of new functions and applications written by network vendors, third-party developers, and even the operators themselves.
- Innovation. The ability to foster innovation along the lines just described is perhaps the most lucrative opportunity for an SDN-enabled network. As a further example, it's possible to write abstracted applications for the network and apply them in a way that's detached from specific vendors, protocols, or geographic environments. These abstracted applications can be specific to use cases (e.g., dynamic congestion management), carrier applications (e.g., mobile video management), technologies (e.g., weather management for microwave links), and more.
These network attributes lay the groundwork for a distributed, programmable, and abstracted infrastructure that can be exploited for faster service delivery and optimized for specific end-user application needs. In addition to the obvious operational benefits (minimized complexity and administration costs), service providers can leverage these attributes to reduce capital spending by improving utilization rate, enabling network defragmentation, and virtualizing network functions.
App-centric service creation
SDN promises the integration of network resources to create what could be described as a unified network operating system or controller infrastructure, one that enables optimal connectivity for end-user applications across multiple layers, domains, vendors, and technologies.
In addition to the high degree of programmability and automation, the important difference from traditional networks and their dependence on predefined sets of resources is that the SDN-enabled network is application-centric (see Figure 2). Not every application has the same set of requirements or priorities, and neither are they billable in the same way nor equally profitable to the service provider. Aligning network resources to serve the performance requirements (e.g., latency, cost) of specific applications and services translates into direct financial benefits for the service providers. In this sense, the operator has the ability to "monetize" network properties such as differentiated resiliency or lack of latency.
In addition, an end-to-end transport network that's more elastic and adaptable creates an innovative framework for new billable applications and services. Taking advantage of this framework for innovation is one of the most important means for service providers to create more sustainable business models and compete more effectively with traditional and new competitors.
Extending SDN from packet to optical domain
The advent of SDN has its roots in the data-center compute/storage environment, with applications of the technology initially focused on packet/electrical switching elements (e.g., routers, Ethernet switches). Applying SDN in service-provider networks, however, requires bridging the packet, circuit, and photonic domains, the latter of which brings with it a very unique set of physical properties and constraints, including the classical tradeoffs between reach and capacity.
It's generally accepted that photonic layer technologies provide the most efficient and cost-effective means for transport-network scalability and resiliency. Recent advances in optical communications have also introduced significantly increased levels of photonic layer flexibility and agility with the deployments of innovations such as flexible grid, ROADMs, and photonic mesh.
The SDN framework is being extended to provide for control mechanisms, both direct and abstracted, for circuit-based WAN transport technologies, including DWDM. Resource orchestration of the photonic layer using an SDN controller, working in cooperation with other controller domains and within an overarching SDN orchestrator, provides the optimal means for extracting the maximum value of photonic layer innovation and enabling efficient multilayer service provisioning across the packet and optical domains.
As discussed earlier, open interfaces and programmability are important tenants of the SDN framework, and that's especially the case when enabling multilayer capabilities. The Open Networking Foundation (ONF) has introduced the OpenFlow standard as an open forwarding plane programming interface between SDN controllers and network resources.
Currently, OpenFlow supports programmability of the connectionless-based data plane of packet routers and switches. Recently, the Optical Working Group within the ONF has defined extensions to enable circuit-oriented services for the optical domain that also take into account optical layer transmission attributes. Prior to the formal release of these updates, members of the ONF can obtain drafts of the updates and begin early development efforts. That's an important initial step in extending SDN from the packet to the optical domain.
SDN by the numbers
SDN is a necessity for the coming network revolution. Furthermore, it has the potential to provide significant financial benefits to operators. These benefits will be derived in five ways.
- The rapid availability of new products and services.
- Decreased times for dimensioning and provisioning resources for applications.
- Reduced complexity associated with provisioning and configuring diverse resources.
- Decreased capex and opex by allowing customers to quickly customize required connection parameters while operators distribute loads to the most appropriate resources with greater efficiency.
- Minimized vendor lock-in and forced upgrade cycles.
SDN is further complemented by virtualization technologies such as NFV and will become increasingly needed as operators are required to serve an ever-expanding suite of applications.
STU BENINGTON is director of the Cloud and SDN Business Unit at Coriant.
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