  The paper [1] presented the first results on generic identifiability of
dynamic networks with partial excitation and partial measurements, i.e.
networks where not all nodes are excited or not all nodes are measured. One key
contribution of that paper was to establish a set of necessary conditions on
the excitation and measurement pattern (EMP) that guarantee generic
identifiability. In a nutshell, these conditions established that all sources
must be excited and all sinks measured, and that all other nodes must be either
excited or measured. In the present paper, we show that two other types of
nodes, which are defined by the local topology of the network, play an
essential r\^ole in the search for a valid EMP, i.e. one that guarantees
generic identifiability. We have called these nodes dources and dinks. We show
that a network is generically identifiable only if, in addition to the above
mentioned conditions, all dources are excited and all dinks are measured. We
also show that sources and dources are the only nodes in a network that always
need to be excited, and that sinks and dinks are the only nodes that need to be
measured for an EMP to be valid.
