Multiparametric Passive Linear Stationary Dynamical Scattering Systems:   Discrete Case, II: Existence of Conservative Dilations
  In the present paper we introduce the notion of dilation of a multiparametric linear stationary dynamical system (systems of this type, in particular passive, and conservative scattering ones were first introduced in func-an/9804130). We establish the criterion for existence of a conservative dilation of a multiparametric passive scattering system. This allows to distinguish the class of so-called $N$-passive systems preserving the most important properties of one-parametric passive scattering systems. 
Dmitriy S. Kalyuzhniy