An entry containing information about one unidirectional
or bidirectional cross-connect on the slave switch
controlled via VSI. A VSI controller represents an instance
of a service layer accessible to a network control application.
The application creates virtual links via service requests to
the controller, which in turn sends commands to the VSI slave,
indicating the participating logical interfaces. Conversely,
links are taken down by a reverse process. Virtual link
creation and deletion come about as a result of routing
decisions.