The next generation network (NGN) architecture defined in Recommendation ITU-T Y.2012 is a generalized architecture in which abstract functional entities are specified. However, to address the issues of interoperability within an NGN network, there is a need to identify physical realizations showing which functional entities are implemented in a network component and by implication theinterfaces that are important to ensure the interoperability of systems. Supplement 64 to the ITU-T Q series of Recommendations provides guidance on the physical realization of NGNs by describing a number of possible physical entities corresponding to a functional entity or a group of functional entities specified in the generalized functional architecture of NGN.