The Big Idea of Software Defined Networks

BTR_Feature_Art_Software_9_16_13 In general, new concepts that cable operators are readying are big news years ahead of implementation: DOCSIS 3.1 and CCAP are two of the most recent examples. A new approach - potentially as beneficial and as disruptive as those two - is approaching without nearly the same fanfare.

It may be that software defined networks (SDNs) are a bit under the radar because they weren't pioneered by cable. Instead, they are an idea that was born on the telecom and data center side.

SDN is a big idea, however - and one for which the industry must prepare.

The Internet has developed in a piecemeal fashion that led to the functionality that oversees where data is to be sent and the functionality that actually executes those commands being co-mingled. SDNs create an "abstraction layer" that sits in the cloud above the hardware and, in the words of the Open Networking Foundation, "decouple[s] the network control and forwarding functions."

Separating these functions and managing devices from a higher level vantage point offers significant advantages in two areas.

The first is that architecting the network in this way makes it far easier to change the flow of data in both the long term and short term. An example of the former is when a new service is added that qualitatively changes the needs of the network. If, for instance, a new streaming service greatly increases the QoS and QoE necessary, the changed parameters can more seamlessly be integrated in an SDN. An example of the short-term benefits of bifurcating the routing and the data forwarding is moving data fluidly around congestion and other unforeseen obstacles and slowdowns.

This is a potent capability. "The controller exists in software and can be located anywhere in the network," said Gaylord Hart, Infinera's (NASDAQ:INFN) director of CATV marketing. "What ends up happening is that the controller has an abstracted view of the network and is not bogged down in the details. It has a high level view of what the network is and what it is doing."

The other benefit of SDNs is that the separation will open the network to true interoperability. When the data routing and packet forwarding functions are wrapped together, it is almost certain that one vendor will dominate that network. It is a proprietary approach. In an SDN environment, the routers, switches and other elements in the network are "dumber" and use standardized protocols. Thus, a network can consist of hardware and software from a wide variety of sources.

SDNs have long been a hot topic in the data center and telecom sectors. They are increasingly gaining attention in the cable industry. The fact that the SDN concept has gotten traction is proven by panels exploring the topic at both The Cable Show last June in Washington, DC, and at Cable-Tec Expo next month in Atlanta.

Cable engineers say that the basic concept of SDNs can be used in multiple areas by cable operators. SDNs are appropriate for the distribution and last mile segments of the networks. They can be used by large MSOs trafficking data between regions and even by federated MSOs cooperating across company boundaries, such as the Cable WiFi consortium that joins Time Warner Cable, Bright House Networks, Comcast, Cablevision and Cox.

That’s a bright future, and the cable industry is moving deliberately on the technology. How it plays out for operators remains to be seen, however. "SDN (and network function virtualization, or NfV) are immature in the carrier space,” wrote Chris Donley, the director of network technologies for CableLabs in response to emailed questions. "There are a number of different technologies being explored in The  European Telecommunications Standards Institute, the Internet Engineering Task Force, CableLabs, and other forums. We have been working with MSOs and our technology partners on SDN and NfV at CableLabs since June 2012. There is definitely growing interest in this transformation; however, in terms of technology development cycles, we're currently in the 'era of ferment.' It will take some more time for these technologies to mature."

Though there is a great deal of uncertainty as to what the final specifications will be - and there is a lot of money on the table, so the deliberations will be high stakes - one certainty is that the changes will be great. "It's a completely different way of architecting networks," said Shridhar Kulkarni,  Aurora Networks' product manager for access network solutions. "It is more software intensive. You are not thinking about boxes anymore. You are thinking about the cloud. That might sound like a cliché, but a lot of intelligence now is remote."

Sharon Barkai, the co-founder of SDN vendor ConteXtream, sees an expansive future in which SDNs act as an overlay network that can devote assets as necessary regardless of distance. Indeed, the abstraction layer upon which SDNs rely can be the key to overcoming the legacy fragmentation that hinders large operators as they deploy technologies such as the Internet Multimedia Subsystems (IMS) and create truly national footprints. In essence, SDNs can serve as a mesh virtualizing internal operations and creating deep links at multiple levels with other service providers both within and outside the cable industry. "We see the opportunity ... to use SDNs on top of IP networks to connect all these functions," Barkai said.

It should be noted that Comcast Interactive Ventures is a major investor in the company, which is deployed with one unnamed MSO, according to Vice President of Marketing Anshu Argarwal.

That is the expansive, long-term vision. The key in the shorter term is to make legacy networks run more smoothly. Cable operators, according to observers, must plan the evolution of their infrastructures with this new approach in mind and ask networking equipment vendors how investments made today will be future-proofed against the day that SDNs become available.

To a perhaps greater extent, however, the precise ways in which operators can avoid stranding investments made before SDNs emerge are unknown. "I don't have specific advice on this question quite yet," Donley wrote. "First, in many cases, these are software features; the actual hardware impact might vary per technology supplier.  Second, we (the industry as a whole) are still working on requirements and architectures for adopting SDN and NfV, so it would be premature to comment on the final solution at this point."

 Carl Weinschenk is the Senior Editor of Broadband Technology Report. Reach him at

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