Software-defined networking for the future

On the Edge

ONF Projects

Most of the current ONF projects target providers and their technology needs, as well as exploit the technologic capabilities of the 5G mobile standard.

SDN-enabled broadband access (SEBA), for example, is a platform for various virtualized access technologies at the edge of the provider's core network and requires relatively few resources. It supports both provisioning broadband connectivity to households and wireless connectivity back to the carrier core. The technology routes traffic directly to the core without having to process virtual network functions on the server. It works with containers and Kubernetes.

Virtual optical line terminal (OLT) hardware abstraction (VOLTHA) builds software that serves the same purpose as broadband access equipment. The approach is vendor agnostic and disaggregated and allows an arbitrary broadband service to be provided as a service. So far, a control and management system for passive optical network (PON) hardware exists. Technology profiles for other access technologies will be launched on the market soon. In the northbound (application) direction, VOLTHA appears to be an SDN controller for a programmable Ethernet switch. VOLTHA communicates with the PON hardware over manufacturer-specific protocols and matching adapters. Certified products are available from Adtran, Edgecore, Radisys, Sercomm, and Zyxel.

Aether is an open source platform that can be used to implement private 5G/LTE edge-to-cloud services. The platform provides mobile connectivity and edge-cloud-managed services at the edges of distributed enterprise networks. The platform is designed for multicloud deployment and enables wireless connectivity in licensed and unlicensed bands. Aether version 1.6 is currently available. Certified products are available from Wiwynn and Sercomm.

SD-Core is an integrated part of Aether. The project implements a disaggregated mobile core for 4G/5G infrastructures for public clouds and the distributed edge clouds connected to them. The technology is a good fit for both carrier and 5G enterprise networks.

Externally, SD-Core presents conventional 3rd Generation Partnership Project (3GPP) interfaces. In combination with Aether, SD-Core can be deployed very quickly. The technology can also be used as a standalone 4G/5G core or as a control and data plane with customer-specific requirements.

Open RAN (O-RAN) is an approach to open remote access implemented over a real-time radio access network (RAN) intelligent controller (RIC). The controller supports xApps that implement higher network functions such as handover, which used to be handled by cellular base stations.

An open source RIC with near real-time capabilities and some xApps are being developed in the scope of the SD-RAN project. The goal of the approach is to accelerate the spread of O-RAN technology through the availability of interoperable components.

SD-Fabric builds on the use of programmable circuits and is a particularly interesting project for corporations. SD-Fabric is a developer-friendly and fully programmable full-stack 5G network fabric that supports future edge applications (e.g., for Industry 4.0) and is manageable in the cloud. SD-Fabric aims to develop custom edge clouds.

To this end, the programmable network resources are provided by software-as-a-service (SaaS) APIs. Developers can develop applications for the edge that impose only a minimal load on the CPU. Custom packet processing can be deeply embedded in network elements and application functions accelerated by P4 functions (more on this later) running on network switches, programmable server network interface cards (NICs), and softswitches, boosting performance while reducing costs and resource requirements. SD-Fabric is also part of Aether and connects all the hardware of an Aether site.

Other Free ONF Projects

Open Network Operating System (ONOS) is envisioned by ONF as the next-generation SDN controller for SDN and NFV deployments. Aligned with the needs of carriers, ONOS supports configuration and real-time control of the entire network. As a result, the network fabric no longer needs to run protocols to control switching and routing, and end users no longer need to modify the data layer when writing new applications. ONOS includes the platform along with a set of applications that act together as an extensible, modular, and distributed SDN controller. New software, hardware, and services are easy to manage, configure, and deploy. The architecture is resilient and scales without limit.

ONOS bundles the best of each of cloud, SDN, and NFV and can be used to implement disaggregated carrier transport networks, edge applications (e.g., central office re-architected as a data center, i.e., CORD), and multitenant data center networks. One practical implementation of this principle is Trellis, a data center network structure based entirely on the spine-and-leaf principle with a multitenant overlay built exclusively on white-box, bare metal hardware.

P4 (programming protocol-independent packet processors) is a domain-specific open source programming language for network devices. It describes how data plane devices (e.g., switches, routers, NICs, and filters) process packets. The programs and compilers are target specific. The target hardware can be field-programmable gate arrays (FPGAs), programmable application-specific integrated circuits (ASICs), or x86 computers. P4 programs classify packets by their headers and handle them accordingly.

P4 compilers generate metadata that the control and data layers can use to communicate with the P4Runtime API. They also create an executable file for the target data layer, in which you can find the header formats and actions of the target system assigned to them. The P4 integrated network stack (PINS) refers to the IT industry's concerted effort to enable legacy routers for SDN and make them accessible for P4 programming, which requires embedded control protocols such as the Border Gateway Protocol (BGP).

Mininet is a development and test environment for SDN networks and applications and is useful for working on laptops. Mininet runs real code, including standard *nix networking applications, the BSD Linux kernel, and the Linux networking stack. Python has an extensible API for network building and experimentation. The most important applications are the rapid generation of SDN prototypes, topology testing without a physical network in place up front, and collaboration of multiple developers on the same topology.

The Open Disaggregated Transport Network (ODTN) project creates data center interconnects with disaggregated optical equipment in line with open and widely used standards and with open source software. Therefore, optical white-box systems from different vendors can be combined on a single platform, which makes it easier for manufacturers to specialize on just a few components, which in turn reduces costs.

The Open Information Modeling and Tooling (OIMT) project develops open information models and related software tools. It is suitable for developing software-defined standard platforms, frameworks, and interfaces that users need to control, manage, and orchestrate SDNs.

Open Mobile Evolved Core (OMEC) is developing a feature-rich, high-performance, and scalable open source evolved packet core (EPC) that connects mobile subscribers to the carrier infrastructure and the Internet. EPCs provide authentication, roaming, billing, and security functions in the form of interconnected services. OMEC is designed to help cope with the myriad of new devices coming online through 5G, IoT, and edge computing.

The Open Transport Configuration and Control (OTCC) project aims to create configuration and control interfaces for interdisciplinary deployment on SDN transport networks. These interfaces are written with open source software and software-defined standards. The transport technologies of network Layers 0 to 2+ can be controlled, which also includes optical and microwave technologies.

XOS defines the highest level of service control, which is the top layer over various back-end service implementations, including virtual network functions (VNFs) on virtual machines and microservices in containers, as well as SDN-based control programs that embed functions in white-box switches.

Proprietary SDN Technologies

Claiming that the entire market uses open standards would be misleading. Proprietary SDN implementations are often found in corporate data centers and on corporate networks, as are hybrid implementations that support SDN in parts of the network and conventional networking mechanisms in others.

VMware's NSX is an example of proprietary virtual networking specifically for the data center. Networks, clouds, and application frameworks can be connected. Networking and security functions run on virtual machines, containers, or bare metal servers. In addition to switching and routing, features include firewalling, load balancing, VPNs, gateway functions for defining and connecting different virtual networks, context-sensitive microsegmentation, container security, and multicloud operation. It also includes an interface for setting up a software-defined data center (SDDC), a command line, automatic troubleshooting during operation, and more.

Cisco's SDN concept for the data center is called Application Centric Infrastructure (ACI). The current ACI version 6 is part of the Nexus Dashboard Platform for Cloud Networking, which provides rules-driven control of cloud and multicloud environments. The Cisco Application Policy Infrastructure Controller (APIC) controls and operates a scalable, multitenant ACI fabric as a central, clusterable appliance. Its features include network rule creation, management and application, data-model-directed declarative provisioning, and application and topology monitoring, including troubleshooting.

Integration with third-party services is supported in Layers 4 through 7 with VMware vCenter and vRealize; Hyper-V, System Center Virtual Machine Manager, and Azure Rack; and Open vSwitch, OpenStack, and Kubernetes. The approach provides a directory of ACI components and their configurations and supports the implementation of a distributed framework across an appliance cluster. ACI also manages the images of spine-and-leaf networks (Figure 2). The functionality of network clients, applications, switches, and other components is monitored, as are errors, events, and performance. Version 6 has improved scalability and timing-critical features, among other things.

Figure 2: Cisco ACI Remote Leaf helps enterprises connect a leaf switch at a remote site to the spine at headquarters and in turn extend its management authority to the remote leaf. © Cisco

The second important component of ACI infrastructures is the Nexus 9000 series switches, which can be used to build spine-and-leaf infrastructures. The devices scale from 1 to 800Gbps Ethernet. They are configurable either for compatibility with earlier generation NX switches or for ACI environments. Different ACI networks (pods) can be combined in an ACI Multi-Pod, which is also an APIC-controlled superimposed network.

The Microsoft variant of SDN, VNet, lets admins configure SDNs in Azure environments with Azure Stack HCI (hyperconverged infrastructure) or on Windows Server 2022 and 2019. According to Microsoft, elements of a Microsoft virtual network such as the Hyper-V virtual switch, Hyper-V network virtualization, load balancing, network controller and remote access server (RAS) gateway are designed from the ground up to be SDN elements.

SDNs can be deployed through the Azure network controller, load balancer, or gateway. Users can choose which of the components they use.

The network controller is the central, programmable automation point for the entire management and configuration of VNet. For example, it handles microsegmentation of virtual local area networks (VLANs) and QoS configuration. It can be implemented either with SDN Express PowerShell scripts or in the Windows Admin Center. The software load balancer uses BGP to switch virtual IP addresses to the physical network. The gateway securely networks SDNs and external customer networks over the Internet and also uses BGP.

Arista's SDN variant, Converged Cloud Fabric (CCF), is designed to enable a cloud-like working experience across an enterprise's network infrastructure (Figure 3). The concept provides for three levels. At the lowest infrastructure level, applications and data reside on virtual machines (VMs), in containers, or on bare metal machines. The next level above is the switching infrastructure with open switches. Arista has tailored its operating system for its SDN switches. Above this is Arista's SDN controller, referred to here as the CCF controller. It has open interfaces to various private cloud platforms, such as VMware, Nutanix, VxRail, Kubernetes, OpenStack, and Microsoft. The CCF controller serves as a central and hierarchically implemented control point and is deployed as a pair of highly available hardware appliances.