SDN in a Foot of Snow?


Understanding the Impact of SDN on Access Networks

Between the data center and the customer premises lies the service provider’s access network, the indispensable connection between the device-enabled subscriber, their Internet of Everything, and cloud-delivered content and applications. Environmentally controlled, software defined data centers with fully meshed pools of resources serve up applications and content for the world, while the industry clamors for x86 white box network products to radically transform the business environment with dynamic on-demand virtual network functions.

But what of the access network? More than simple connections, the access network literally bridges the consumer to endless opportunities for entertainment, knowledge, and so much more. To remove impediments to the boundless appetite of consumers and become an enabler of new service revenue for the service provider, the access network must evolve, taking in the best of the data center’s software defined architecture, and melding it with the hard realities of the access network.

The move to cloud computing and networking is a fundamental shift that impacts every consumer of networked services. The basic Software Defined Networking (SDN) architecture separates the management and control planes from the forwarding plane, thus allowing each part of the network — applications, management, control, and forwarding — to be independently optimized in a way that is scalable and open to fast-paced innovation. The underlying network infrastructure is abstracted from the applications and network services, but connected with open application layer interfaces (APIs) to allow direct programmability of each component of the network.

Network Functions Virtualization (NFV), an inextricably linked partner of SDN, has moved discrete functions once embedded in network hardware into software that can run in virtual machines located “virtually” anywhere in the world.

The origins of virtualization and software defined networks started in the enterprise with virtualized servers replacing physical servers. This enterprise architecture moved to the data center as a means to optimize infrastructure, but quickly evolved to an entire ecosystem of software defined data centers supporting a myriad of cloud services and virtualized network elements. The challenge now is to move the SDN architecture and virtualization technologies from the data center into the outside plant, creating Software Defined Access as a complement to the SDN-enabled data center.

The Challenges of 
Access Networks
The challenges that access networks impose on an SDN architecture are physical, technological, and service oriented. At a quick glance, it is obvious that access network equipment is subject to extremes of temperature and weather. Topologically, access networks are distribution networks, usually with single points of aggregation (e.g., a DSLAM or GPON OLT) and non-redundant outside plant facilities.

Systems equipment is often hard to reach and replace, and as a result is designed to compensate for faults with expensive and complex hardware. A typical system software upgrade involves a coordinated dance between active and standby system controllers, each compensating for software that is tightly integrated and coupled to the hardware.

In the access network, a system provides a single, non-redundant connection for thousands of customers, even when it’s under a foot of snow. There is no virtualized pool of compute resources that can simply off-load subscriber services, yet communication services are critical infrastructure and in use 24 hours per day, 7 days per week.

There is no time or place for a network maintenance window. The access network of the future will still live under a foot of snow, but it must operate in a manner that emulates that of a data center. (See Figure 1.)

Figure 1. Multiservice access network with single aggregation point providing subscriber services over multi-generational access technologies.

Figure 1. Multiservice access network with single aggregation point providing subscriber services over multi-generational access technologies.

The access network undergoes a higher rate of change at the physical layer than any other part of the communications network. Consider the following (incomplete) history of broadband technologies:
• G.dmt, G.lite, ADSL2, ADSL2+, VDSL, VDSL2, plus bonded versions
•, Amendment 2,, plus bonded versions
• TDM (POTS), ATM, Ethernet
• Copper, Coax, Fiber, Wi-Fi
• Home networking from consumer products (, home automation)

These short lists are an impressive collection of co-linear technologies that changed the lives of broadband subscribers in very dramatic, positive ways. Each technology improved access speeds and improved the subscriber experience, to the point where broadband subscribers in the US now frequently enjoy gigabit speeds, and spend an average of 7.4 hours per day on the Internet (Source: KPCB Internet Trends,

With these incredible technology advances invariably came a new chipset, and usually a new vendor-
specific software development toolkit and capabilities for the systems vendor. For the service provider, each technology advancement often came with a new service definition, new methods and procedures (MOPs), large certification cycles, and new back-office system integration — an expense borne only because of the large number of subscribers over which the costs could be spread. OSS integration for an access service provider equates to subscriber management, billing, customer support, and compliance with law enforcement (CALEA) — in essence, everything that makes a service provider a “service” provider. Each highly sought after technology advance makes the lives of the access system vendor and service provider a painful race toward a brief self-destructive re-invention.

Software Defined Access
A list of differences between the data center and the access network could be long and daunting, yet only a short list would be sufficient to highlight the redundancy, automation, virtualization, physical, and lifecycle differences. Simply lifting the infrastructure and software from the data center and re-using in the access network will not work in a generalized case.

At the intersection of SDN architecture and broadband access lies Software Defined Access, an architecture that leverages the best of data center software design and network virtualization, extended across the outside plant to accommodate the environment and variability of the ever-changing physical layer of the access network. (See Figure 2.) The access network of the future will accommodate multiple physical technologies while delivering a non-stop service with consistent OSS integration. Combining the best of the SDN architecture with the realities of the access network results in the following defining attributes of Software Defined Access:

Figure 2. SDN in the access network evolves from data center architectures adapted for service distribution.

Figure 2. SDN in the access network evolves from data center architectures adapted for service distribution.

To be successful, next-generation access solutions must incorporate SDN-inspired best-of-breed technologies in programming, development tools, and network OS design — adapted for the unique access network environment.

Software Defined Access rapidly delivers new services, a superior customer experience, and unparalleled reliability — wherever your access network calls home.


About Author

Shane Eleniak is responsible for product strategy, positioning, and systems roadmaps at Calix. He has more than 25 years of experience in the telecommunications industry. Prior to joining Calix, Shane was the Group VP of the ABS business unit at CommScope, responsible for all edge, access, and CPE products within the Broadband Division. Earlier, at Alloptic, he guided product, sales and corporate strategy to deliver the industry's first 10G EPON and RFoG products. For more information, please email or visit

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