Earlier this month, the SDN use case for broadband access progressed further within the open networking consortiums. AT&T submitted the first version of Virtual Optical Line Termination Hardware Abstraction (VOLTHA) software-defined access (SD-Access) specification into the Open Networking Foundation (ONF). VOLTHA provides a framework to support broadband access in the cloud, pairing nicely with the Central Office Rearchitected as a Datacenter (CORD) initiative. Regarding CORD, it was AT&T, again, and other forward thinking service providers that partnered with ON.Labs several years ago to develop the architecture. The goal of CORD is to provide a reference architecture for SD-Access evaluation platforms for field trial on commercial operator networks. It should be noted that ON.Labs was folded into ONF around a year ago, so CORD, VOLTHA and (Open Networking Operating System) ONOS all fall under the purview of the ONF.

What is VOLTHA and what’s it good for? Basically, as the name suggests, VOLTHA provides an abstraction layer for SD-Access architectures sitting between PON devices (OLT and ONUs) and open SDN controllers providing network management and service orchestration. In the future, VOLTHA will not only support any PON component whether based on GPON, XGS-PON, NG-PON2, 10G-EPON, but any broadband access component: Gfast DPU, R-MAC/PHY, fabric and aggregation switches are some examples. This mediation between agnostic open SDN orchestrators (ONOS–based controller, for example), the vendors (ADTRAN, etc.) and the domain-specific broadband access devices (access, edge, transport) greatly simplifies and expedites IT changes. VOLTHA communicates with these hardware devices using vendor-specific protocols and protocol extensions through adapters, streamlining multi-vendor interoperability challenges between devices.

In short, VOLTHA makes all OLTs, ONUs and very soon Gfast DPUs look the same to the SDN controller regardless of vendor or domain. This greatly accelerates the time-to-market for new network component introduction supporting the creation of best-in-breed networks. This abstraction also allows VOLTHA to bolster the microservices and DevOPs models, simplifying the creation of new subscriber and operational services. You can think of it this way, the broadband access devices are abstracted to become programmable Ethernet switches (PON OLT as a switch, Gfast DPU as a switch, 5G fronthaul as a switch). VOLTHA is the next step toward the creation of true virtualized access equipment supporting the separation of control and data planes.

“This software allows us to take white and gray boxes from multiple vendors,” explained Eddy Barker, assistant vice president for technology design and architecture at AT&T. “We have been doing lab evaluations now with four vendors, with their implementation of ONOS and VOLTHA controlling seven different white boxes. The plan is to pick two of them as part of our trial plans this year.”

I would say it is the job of these four vendors to not only show their SD-Access equipment performs admirably using VOLTHA 1.0 software, but provides the necessary carrier-grade feature set required to support mass-market implementations of CORD or “secret sauce,” as Eddy at AT&T put it. A few that easily come to my mind from our experience are providing abstraction from provider specific OSS/IT abstraction (TL1, XML, MTOSI) and open SDN controllers and providing missing critical network management features needed to harden these open-source network controllers and service orchestrators.

“Open source is for collaboration for lowering the cost of software and capabilities, but we’re still going to need an ecosystem that’s made up of hardware suppliers and have vendors that take open source software and harden and scale it,” Barker said. “We’re going to need that integration to bring things together, but there may be parts of the ecosystem that can be secret sauce.”

2018 is sure to be a watershed year for CORD field trails. ADTRAN currently has over 25 lab trails of CORD-compliant SD-Access solutions globally with more on the way. At Broadband World Forum 2017 in Berlin next week, ADTRAN, ONF and AT&T will surely all be highlighting and maybe even demonstrating live working CORD-based SD-Access architectures utilizing VOLTHA abstraction.

Kurt Raaflaub leads ADTRAN’s strategic solutions marketing, and has more than 20 years of experience in telecom.