 power and cooling systems of a network element). The parts of a physical network that are closest to concrete components are physical media connections, which were discussed in Sect. 2.2. This concept is, however, interpreted in the OSI sense, which means that a physical medium is defined only by its transmission characteristics (electromagnetic proper- ties). Since real media also have spatial properties, we must conclude that we can- not deal with spatial properties in functional space. Therefore, the physical nodes we define in functional space do not represent completely specified concrete systems. We must make a distinction between physical nodes and concrete sys- items. This does not mean that spatial properties are less important in systems model- ling. Spatial space is very important for designing all kinds of packaging structures (e.g. IC- and PC-layout planning), and, in telecommunication system design, for network planning. Spatial space is defined by four spatial dimensions (X, Y, Z, Time). Spatial space suits the description of properties that have spatial dependen- cies, as shown in Fig. 2.42. To the left in Fig. 2.42, the shape or spatial dimensions of a concrete system are described. The middle part shows the path a moving mobile system (a mobile phone, a satellite, etc.) travels in spatial space. To the right, the carrier-to-interference ratio (C/I), which determines the reuse of frequen- cies in cellular networks, is analysed. This property has a spatial dependency, and must therefore be modelled in spatial space. 2.3 Architectural Principles C/I > ca 10 dB Concrete system unit of distance base station Fig. 2.42 Modelling in spatial space Providing complete descriptions of a concrete network (which has both func- tional and spatial properties) requires defining mapping between the physical nodes that are defined in functional space and the concrete systems that are defined in spatial space, as indicated in Fig. 2.43. exists_in Concrete Physical system Fig. 2.43 Mapping between functional and sp