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Published: Mar 9, 2022 License: Apache-2.0



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The µONOS Topology subsystem provides topology management for µONOS core services and applications. The topology subsystem structures the topology information as a set of objects, which can be either Entity, Relation or a Kind.

  • Entity objects are nodes in a graph and are generally intended to represent network devices, control entities, control domains, and so on.
  • Relation objects are edges in a graph and are intended to represent various types of relations between two Entity objects, e.g. contains, controls, implements.
  • Kind objects can be thought of as template or schema objects that represent an entity or a relation kind. Strictly speaking, Entity or Relation instances do not have to be associated with a Kind, but maintaining Kind associations can be used for schema validation and speeding up queries and is therefore highly encouraged.


The onos-topo subsystem exposes the topology information via a gRPC API that supports the above abstractions.

Unique ID

Each Entity, Relation and Kind objects has a unique identifier that can be used to directly look it up, update or delete it.


The Entity and Relation objects themselves carry only the essential information for identifying them, associating them with a particular kind and in case of Relation, for associating the two - source and target - Entity objects. Clearly, while this is necessary, it is not sufficient to allow the platform or applications to track other pertinent information about the entities and relations.

Since different use-cases or applications require tracking different information, and these may vary for different types of devices or network domains, the topology schema must be extensible to carry various aspects of information. This is where the notion of Aspect comes in. An Aspect is a collection of structured information, modeled as a Protobuf message (although this is not strictly necessary), which is attached to any type of object; generally mostly an Entity or a Relation.

Each object carries a mapping of aspect type (TypeURL) and Protobuf Any message. For example, to track a geo-location of a network element, one can associate onos.topo.Location instance, populated with the appropriate longitude and latitude with the Entity that represents that network element, with the Location being defined as follows:

// Geographical location; expected value type of "location" aspect
message Location {
    double lat = 1;
    double lng = 2;

Similarly, to track information about the cone of signal coverage for a radio-unit, one can attach onos.topo.Coverage instance to an Entity representing the radio unit, with Coverage being defined as follows:

// Area of coverage; expected value type of "coverage" aspect
message Coverage {
    int32 height = 1;
    int32 arc_width = 2;
    int32 azimuth = 3;
    int32 tilt = 4;

The current list of aspects defined in onos-api includes the following:

  • onos.topo.Asset - basic asset information for the device: model, HW, SW versions, serial number, etc.
  • onos.topo.Location - geo location coordinates
  • onos.topo.Configurable - info for devices that support configuration via gNMI
  • onos.topo.MastershipState - for tracking mastership role
  • onos.topo.TLSOptoins - TLS connection options
  • onos.topo.Protocols - for tracking connectivity state of supported device control protocols
  • onos.topo.Coverage - radio unit signal coverage cone information
  • onos.topo.E2Node - information about an O-RAN E2 node
  • onos.topo.E2Cell - information about an O-RAN E2 cell
  • onos.topo.AdHoc - for tracking ad-hoc key/value string attributes (not labels)

The above are merely examples of aspects. Network control platforms and applications can supply their own depending on the needs of a particular use-case.


To assist in categorization of the topology objects, each object can carry a number of labels as meta-data. Each label carries a value.

For example the deployment label can have production or staging or testing as values. Or similarly, tier label can have access, fabric or backhaul as values to indicate the area of network where the entity belongs.


The topology API provides a List method to obtain a collection of objects. The caller can specify a number of different filters to narrow the results. All topology objects will be returned if the request does not contain any filters.

  • Type Filter - specifies which type(s) of objects - Entity, Relation or Kind - should be included.
  • Kind Filter - specifies which kind(s) of objects should be included, e.g. contains, controls
  • Labels Filter - specifies which label name/value(s) should be included, e.g. tier=fabric
  • Relation Filter - specifies target entities related to a given source entity via a relation of a given kind

Support for other filters may be added in the future.


The topology subsystem is available as a Docker image and deployed with Helm. To build the Docker image, run make images.

See Also


Path Synopsis
Package manager is is the main coordinator for the ONOS topology subsystem.
Package manager is is the main coordinator for the ONOS topology subsystem.

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