What is ONOS (Open Network Operating System)?
ONOS (Open Network Operating System) is an OS designed to help network service providers build carrier-grade software-defined networks architected for high scalability, availability and performance.
Although specifically designed to address the needs of service providers, ONOS also acts as a software-defined networking (SDN) control plane for enterprise campus local area networks and data center networks.
In December 2014, Open Networking Lab (ON.Lab) released the ONOS source code, written in Java, to the open source community. In October 2015, the ONOS project joined The Linux Foundation as a collaborative open source project.
New ONOS releases come out quarterly in February, May, August and November. Each release is named after a bird, which is the ONOS logo. Releases include Avocet, Loon, Woodpecker and Velociraptor. As with most open source projects, ONOS has a GitHub page where collaborators can contribute changes to the code.
Both service providers and vendors contribute to ONOS. Service provider contributors include AT&T, NTT Communications and China Unicom. Vendor contributors include Adtran, Edgecore Networks, Intel, NEC and Ciena.
ONOS has multiple use cases. One of the most well known is ON.Lab's Central Office Re-architected as a Datacenter (CORD). This was created to transform telecom carrier central offices into more scalable environments, similar to next-generation data centers. Virtual network functions and customer premises equipment help accomplish this transformation. ONOS is one of the open source software systems used to manage CORD.
How ONOS works
The ONOS core is based on a modular architecture, as opposed to an integrated system that blurs the division between its components. This modularity keeps north-south and east-west workflows separated, while also permitting easier customization for the entire system.
Because service providers require network scalability, the ONOS controller can scale out to accommodate a physically distributed system of devices. This scalability enables service providers to add new components without disturbing the rest of the system. Additionally, the distributed architecture reduces network failure, as identical instances pick up where another fails. This, in turn, results in high availability.
While ONOS has a distributed core to provide reachability to each network switching device, the ONOS controller remains logically centralized. Separate subdivisions or instances in the complete ONOS architecture are accessible as a single system. For overall system visibility and management, ONOS provides a relatively straightforward graphical user interface.
ONOS features northbound and southbound application programming interfaces (APIs) grounded in abstraction to prevent configuration and protocol lock-in for applications and devices.
For northbound interactions, ONOS uses its Intent Framework subsystem, which enables applications to specify what they need from the system, such as more bandwidth. Once an application declares its needs, the system configures accordingly. ONOS architecture supports an estimated 1 million application intent requests each second. This capability upholds the system's high performance for the application requests and low latency that service providers need.
Each ONOS instance interacts with the network environment and devices through a southbound API that communicates with lower-level components. The core discovers which protocols can be used to interact with the device, and the southbound API uses that protocol to interact with the device. This is an abstracted API, so ONOS remains unaffected by specific protocols, such as OpenFlow and Network Configuration Protocol, as well as command-line interfaces.
ONOS vs. OpenDaylight
OpenDaylight (ODL) is a similar open source project created by The Linux Foundation. Both ONOS and ODL have modular designs and similar goals to advance SDN.
The two projects take separate approaches, however, and have different backers and partners. While ONOS is primarily for service provider networks, ODL focuses on data center networks. The goal of ONOS is to provide better overall network performance, while ODL merges legacy networks with SDN.
