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.
