ribed only in terms of the properties of and the event types in network service interfaces. Therefore, a logical network structure therefore holds for any kind of distribution solution. 2 Foundations of Sysnet Modelling The physical structure of the network defines which network interfaces exist in the D-dimension. By definition, a network interface defines all communication relations between two physical nodes. Physical nodes are entities that termi- nate physical media, i.e. they own physical media connection endpoints. How these two definitions affect each other is shown in Fig. 2.33, which shows the same network we discussed in Fig. 2.11. The model at the bottom of Fig. 2.33 is a model in the D-dimension only (i.e. the C-dimension is collapsed). It introduces the con- cepts and symbols for network interfaces. The model shows that: Some network interfaces comprise physical media, others do not. The symbol for network interface distinguishes between these two possibilities. From the physical network point of view, a physical node may support several network interfaces, which can be of both kinds. network interfaces Network interface with physical medium without physical medium Physical Fig. 2.33 Network interfaces The DC-plane part of functional space is used to model the structure of a net- work, including physical media connections and such functions that are visible on the network level (in terms of protocols and network service interfaces). The DC- plane corresponds, more or less, to the OSI RM. However, the OSI RM does not consider the processing aspects inside physical nodes, which, as we will see, is an important aspect of network characteristics, as well as of the physical structure of a network. The implementation of a logical node in a physical node must be supported by a number of processing services that are provided by an operating system or a telecom-oriented platform in the physical 2.3 Architectural Principles node in which it exists. As a minimum, the latter must provide a connectivity serv- ic