ONF advances its vision for the network edge

The Open Networking Foundation’s (ONF) goal to create software-driven architectures for the network edge has advanced with the announcement of its first reference designs.

In March, eight leading service providers within the ONF - AT&T, Comcast, China Unicom, Deutsche Telekom, Google, NTT Group, Telefonica and Turk Telekom - published their strategic plan whereby they would take a hands-on approach to the design of their networks after becoming frustrated with what they perceived as foot-dragging by the systems vendors.  

Timon SloaneThree months on, the service providers have initial drafts of the the first four reference designs: a broadband access architecture, a spine-leaf switch for network functions virtualisation (NFV), a more general networking fabric that uses the P4 packet forwarding programming language, and the open disaggregated transport network (ODTN).  

The ONF also announced four system vendors - Adtran, Dell EMC, Edgecore Networks, and Juniper Networks - have joined to work with the operators on the reference design programmes.

“We are disaggregating the supply chain as well as disaggregating the technology,” says Timon Sloane, the ONF’s vice president of marketing and ecosystem. “It used to be that you’d buy a complete solution from one vendor. Now operators want to buy individual pieces and put them together, or pay somebody to do it for them.”

We are disaggregating the supply chain as well as disaggregating the technology 

CORD and Exemplars

The ONF is known for various open-source initiatives such as its ONOS software-defined networking (SDN) controller and CORD. CORD is the ONF’s cloud optimised remote data centre work, also known as the central office re-architected as a data centre. That said, the ONF points out that CORD can be used in places other than the central office.

“CORD is a hardware architecture but it is really about software,” says Sloane. “It is a landscape of all our different software projects.”

However, the ONF received feedback last year that service providers were putting the CORD elements together slightly differently. “Vendors were using that as an excuse to say that CORD was too complicated and that there was no critical mass: ‘We don’t know how every operator is going to do this and so we are not going to do anything’,” says Sloane.   

It led to the ONF’s service providers agreeing to define the assemblies of common components for various network platforms so that vendors would know what the operators want and intend to deploy. The result is the reference designs. 

The reference designs offer operators some flexibility in terms of the components they can use. The components may be from the ONF but need not be; they can also be open-source or a vendor’s own solution.

Source: ONF

The ONF has also announced the exemplar platforms aligned with the reference designs (see diagram). An exemplar platform is an assembly of open-source components that builds an example platform based on a reference design. “The exemplar platforms are the open source projects that pull all the pieces together,” says Sloane. “They are easy to download, trial and deploy.”   

The ONF admits that it is much more experienced with open source projects and exemplar platforms that it is with reference designs. The operators are adopting an iterative process involving all three - open source components, exemplar designs and reference designs - before settling on the solutions that will lead to deployments. 

Two of the ONF exemplar platforms announced are new: the SDN-enabled broadband access (SEBA) and the universal programmable automated network (UPAN).

Reference designs 

The SEBA reference design is a broadband variant of the ONF’s CORD work and addresses residential and backhauling applications. The design uses Kubernetes, the cloud-native orchestration system that automates the deployment, scaling and management of container-based applications, while the use of the OpenStack platform is optional. “OpenStack is only used if you want to support a virtual machine-based virtual network function,” says Sloane. 

Source: ONF

SEBA uses VOLTHA, the open-source virtual passive optical networking (PON) optical line terminal (OLT) developed by AT&T and contributed to the ONF, and provides interfaces to both legacy operational support systems (OSS) and the Linux Foundation’s Open Networking Automation Platform (ONAP). 

SEBA also features FCAPS and mediation. FCAPS is an established telecom capability for network management that can identify faults while the mediation presents information from FCAPS in a way the OSS understands.

“In its slimmest implementation, SEBA doesn’t need CORD switches, just a pair of aggregation switches,” says Sloane. The architecture can place sophisticated forwarding rules onto the optical line terminal and the aggregation switches such that servers and OpenStack are not required. “That has tremendous performance and scale implications,” says Sloane. “No other NFV architecture does this kind of thing.”  

The second reference design - the NFV Fabric - ties together two ONF projects - Trellis and ONOS - to create a spine-leaf data centre fabric for edge services and applications.  

The two remaining reference designs are UPAN and ODTN. 

UPAN can be viewed as an extension of the NFV fabric that adds the P4 data plane programming language. P4 brings programmability to the data plane while the SDN controller enables developers to specify particular forwarding behaviour. “The controller can pull in P4 programs and do intelligent things with them,” says Sloane. “This is a new world where you can write custom apps that will push intelligence into the switch.”     

Meanwhile, the ODTN reference design is used to add optical capabilities including reconfigurable optical add-drop multiplexers (ROADMs) and wide-area-network support.

There are also what the ONF calls two trailblazer projects - Mobile CORD (M-CORD) and CORD - that are not ready to become reference designs as they depend on 5G developments that are still taking place.

CORD represents the ONF’s unifying project that brings all the various elements together to address multi-access edge cloud. Also included as part of CORD is an edge cloud services platform. “This is the ultimate vision: what is the app store for edge applications?” says Sloane. “If you write a latency-sensitive application for eyeglasses, for example, how does that get deployed across multiple operators and multiple geographies?”

The ONF says it has already achieved a ‘critical mass’ of vendors to work on the development of the reference designs three months after announcing its strategic plan. The supply chain for each of the reference designs is shown in the table.

Source: ONF

“We boldly stated that we were going to reconstitute the supply chain as part of this work and bring in partners more aligned to embrace enthusiastically open source and help this ecosystem form and thrive,” says Sloane.  “It is a whole new approach and to be able to rally the ecosystem in a short timeframe is notable.” 

Our expectation is that at least two of these reference designs will go through this transition this year. This is not a multi-year process.

Next steps 

It is the partner operators that are involved in the development of the reference designs. For example, the partners working on ODTN are China Unicom, Comcast and NTT. Once the reference designs are ready, they will be released to ONF members and then publicly. 

However, the ONF has yet to give timescales as to when that will happen. “Our expectation is that at least two of these reference designs will go through this transition this year,” says Sloane. “This is not a multi-year process.”