The link between software-defined networking and passive optical LANs

Enterprise networks deploying SDN can achieve additional benefits with a passive optical LAN architecture

Nov 20th, 2017
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The evolution of service providers’ networks may foreshadow developments in enterprise LAN environments.

By Patrick McLaughlin

Passive optical local area networks (passive optical LANs) are a prime and current example of a technology developed for fiber-to-the-home/fiber-to-the-X networks making its way into the enterprise. For several years organizations and groups—particularly including the Association for Passive Optical LAN (APOLAN)—have emphasized that passive optical LANs incorporate proven technologies that have served FTTx networks for years.

In a white paper titled “Smarter Networks with Passive Optical LANs,” which is available for download from the APOLAN’s website, experts from IBM begin by stating, “In the 1980s and 1990s, optical communications revolutionized long-haul transmission. Today, the long distance and underwater communications are the backbone of every major provider consisting of optical fiber. The technology has shown to be vastly superior to copper in terms of bandwidth, range, consumed power, longevity and reliability. Recent advances in the manufacturing and commercialization of passive optical components are now extending these capabilities to the edge and campus networks.

“Buildings that have been traditionally wired with Cat 5/6 copper are facing fantastic opportunity from the emergence of passive optical LAN technology.”

To the extent that passive optical networking technology now has been adopted in enterprises, the technological evolution taking place in service-provider networks today may be a precursor to what will happen in enterprise environments eventually. That possibility came to this author’s mind during a recent conversation with a sales executive at Tellabs, who pointed out that passive optical LANs can help enterprises facilitate software-defined networking (SDN).

This article explores potential links between SDN ans passive optical LANs.

VOLTHA, ONF, CORD and more

On October 5, AT&T Labs’ associate vice president for technical design and architecture, Eddy Barker, revealed in a blog post that AT&T released the Virtual Optical Line Termination Hardware Abstraction (VOLTHA) into the Open Networking Foundation. “This is the first major open-source software release that provides the ‘brain’ for XGS-PON technology,” Barker said. “It also delivers on our commitment to move toward open source software and SDN/NFV [network function virtualization] frameworks.”

Barker further explained that XGS-PON is a passive optical network that promises “broadband connectivity up to 10 Gbits/sec. XGS-PON is a fixed wavelength symmetrical 10-Gbit/sec passive optical network technology. It can coexist with the current-generation GPON [Gigabit Passive Optical Network] technology and provide 4x faster downstream bandwidth. It’s as cost-effective as GPON.”

The Open Networking Foundation describes itself as “a non-profit operator-led consortium driving transformation of network infrastructure and carrier business models … The ONF serves as the umbrella for a number of projects building solutions by leveraging network disaggregation, white box economics, open source software and software defined standards to revolutionize the carrier industry.”

One of the ONF’s projects is CORD—Central Office Rearchitected as a Datacenter. “The edge of the operator network (such as the central office for telcos and the headend for cable operators) is where operators connect to their customers,” the ONF says. “CORD is a project intent on transforming this edge into an agile service delivery platform enabling the operator to deliver the best end-user experience along with innovative next-generation services.

“The CORD platform leverages SDN, NFV and cloud technologies to build agile data centers for the network edge.,” ONF continued. “Integrating multiple open source projects, CORD delivers a cloud-native, open, programmable, agile platform for network operators to create innovative services.”

CORD is packaged into three solutions for different market-use cases, ONF explained. M-CORD supports 5G mobile edge services with disaggregated and virtualized radio, and an open source mobile core. R-CORD supports residential subscribers over wireline access technologies like GPON, G.fast, 10GPON and DOCSIS. E-CORD supports enterprise services such as virtual private networks and application optimization (software-defined WAN) over metro and wide area networks.

The VOLTHA 1.0 release is a notable milestone for the CORD project. AT&T’s Barker stated that major software releases like it “are necessary to fulfill our vision of a software-defined network, which employs NFV. We expect to have 55 percent of our networks virtualized by the end of 2017. We aim to have 75 percent of our traffic on our software-defined network by 2020, and we’re pushing hard to beat that goal.

“Open software efforts benefit the industry because we rely on the active participation and feedback form a large community of developers,” he added. “Developers can improve, add, and influence changes to the software that will help us deliver XGS-PON technology to customers quickly. We are currently performing proof-of-concept testing of VOLTHA in our labs and are planning to deploy XGS-PON field trials before the end of 2017.”

How POL fits

Back to the chat with the Tellabs sales exec who mentioned passive optical LAN and SDN in the same sentence … it will be a very long time before anything like VOLTHA makes its way into mainstream enterprise networking. But SDN is a timely topic for the LAN. In a document aimed at federal-government users, Tellabs declares that passive optical LAN offers the best architecture for software-defined LANs. It explains that as government network administrators evaluate the merits of SDN functionality in buildings and across campuses, they are doing so “under the assumption that SDN fixes traditional LAN operational efficiencies, security and reliability shortcomings. However, what they don’t realize is that by bolting-on SDN as an overlay to a legacy LAN design, they leave the inherent weakness of traditional LANs.”

Pointing the finger at the traditional LAN architecture, Tellabs further contends, “Adding complexity with SDN can marginally improve LAN operational efficiencies, security and reliability, but by introducing more sophistication, the fixes can negatively contribute to the same attributes they were intended to repair. Furthermore, there are alternative means of addressing the underlying fundamental faults relative to traditional LAN … that specifically fix root problems.”

Passive optical LAN, Tellabs explains, is one such alternative means. The company points out the following potential pitfalls of implementing SDN as an overlay to a traditional LAN.

  • Access, aggregation, distribution, and work-group switches are complex, full-functioning devices, representing potential security weaknesses.


  • Complex full-functioning switches spread across buildings and a campus equals distributed intelligence and management at each port, thereby requiring local provisioning, troubleshooting and management of higher-level IP and Layer 3 functions at each port.


  • Adding SDN protocols to existing full-functioning switches inserts security, operation, and reliability complexities.


Conversely, Tellabs argues, an optical LAN “marries the best features of passive optical networking with advanced Ethernet functionality. It does so within the framework that matches cloud, wireless, hosted/managed services, data center and SDN architecture—all of which have the common trait of having centralized intelligence and management.” Plus, a passive optical LAN can define network resources in software, and dynamically allocate them based on real-time demands.

Furthermore, the company stresses, passive optical LAN facilitates SDN implementation in part because “simple unmanaged ONTs [optical network terminals] are better suited for SDN rather than complex full-functioning traditional switches,” and because a passive optical LAN “will allow a mixture of G-PON, XGS-PON, and NG-PON2 [40G] technology choices simultaneously, without the rip-and-replace of today’s infrastructure.”

As IBM’s white paper pointed out, optics changed service-provider networks in the 1980s. It was about 2010 when passive optical LAN technology took hold in enterprise networks. It may be decades before the fruits of the ONF’s efforts are enjoyed by enterprise networks—if they ever are. Nonetheless, proponents of passive optical LANs are pointing to history to make their case for what the future will hold.

Patrick McLaughlin is our chief editor.

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