OpenDaylight is getting the ability to subscribe to changes within switches and routers. We need this because continuous, periodic polling of data is not adequate for applications requiring frequent/prompt updates of remote object state. Having such a capability will address problems including:
The YANG PUBSUB project in OpenDaylight Beryllium addresses these problems by allowing applications to setup customized subscriptions on specific subtrees of YANG datastores in the network. With change-triggered subscriptions, any changes in interesting YANG objects will be pushed to OpenDaylight without any need to explicitly poll the data. Effectively, we are enabling a telemetry solution with customized YANG object delivery by subscriber.
More on the capability can be understood from the IETF NETCONF technology specification draft-ietf-netconf-yang-push, or the I2RS requirements draft-ietf-i2rs-pub-sub-requirements.