YANG [RFC6020] was originally designed for the Netconf protocol

[RFC6241], which originally put most emphasis on configuration.

However, YANG is not restricted to configuration data. ?YANG

datastores, i.e. datastores that contain data modeled according using

YANG, can contain configuration as well as operational data. ?It is

therefore reasonable to expect that data in YANG datastores will

increasingly be used to support applications that are not focused on

managing configurations but that are, for example, related to service

assurance.

Service assurance applications typically involve monitoring

operational state of networks and devices; of particular interest are

changes that this data undergoes over time. ?Likewise, there are

applications in which data and objects from one datastore need to be

made available both to applications in other systems and to remote

datastores [I-D.voit-netmod-yang-mount-requirements]

[I-D.clemm-netmod-mount]. ?This requires mechanisms that allow remote

systems to become quickly aware of any updates to allow to validate

and maintain cross-network integrity and consistency.

Traditional approaches to remote network state visibility rely

heavily on polling. ?With polling, data is periodically explicitly

retrieved by a client from a server to stay up-to-date.