 network becomes integrated in a concrete network, and physical nodes get physical addresses as well. This form of integration is, however, outside SM&AML. A physical node can be removed from a site or added to a site (electrically and/ or physically). In this context we can say that the physical node has a temporary existence in a concrete network. Changes of this kind are performed by network operator activities, partly through the portion of the management system that handles physical network aspects. This form of temporary existence of physical nodes is also outside SM&AML. From a functional point of view, a physical network model is the most complex type of model, since it is created by integrating models from all lower integration levels of the integration hierarchy. An indispensable aspect of a physical network model is, therefore, that it holds together all other types of models that belong to the same sysnet model. It is important that a formal notation is used, SO that models on lower integration levels can be accessed through the physical network model. From a specification point of view, a physical network is fairly simple to pro- duce, since it only adds a node platform (the P-dimension) to what is already described by models on lower integration levels. The only real important specifica- tion aspect beyond that is to define the hierarchy of physical substructures in a sys- net. This structure constrains the extent of models on higher abstraction levels (or, in other words, defines the specification domain for those models). It is absolutely T. Muth, Modeling Telecom Networks and Systems Architecture © Springer-Verlag Berlin Heidelberg 2001 4 Physical Network Modelling necessary to define and manage this structure. As we saw in Sect. 2.3.6, each phys- ical node defines its own (internal) functional space, and functional spaces between physical network levels are completely orthogonal (i.e. independent). If this struc- ture is not managed, substructures can no longer be treated as black boxes. Func- t