. 4.1 Basic physical network terminology The model might describe the complete physical network in a sysnet, or just be a model fragment. As in all model fragments, a physical network model fragment consists of some physical nodes that belong to the model (closed boxes), and others that are out- side the model (open boxes). Properties of physical nodes that are inside the model can be accessed through the model. Properties of physical nodes that are outside the model are accessed through another physical network model frag- ment in the sysnet model, unless the node is also outside the sysnet model. A physical node must terminate at least one physical media endpoint, but can terminate thousands. The interconnection structure that is defined by physical media connections exists only in the D-dimension. In other words, it does not define which network service interfaces and logical nodes exist inside physical nodes. Neither does it define which protocols are used in communication between physical nodes, or which node platforms are used inside physical nodes. Figure 4.1 also shows that the D-dimension is not a linear dimension, but defines a graph where the vertices are physical nodes, and the arcs are physical media connections. When mapped on a spatial model, physical nodes and media connections become allocated in the linear dimensions of spatial space. There are numerous types of media. Physical media symbols are defined only for the basic classes of physical media. Physical media are classified as either wire- line media (twisted pair, coax, optical fibre, etc.) or wireless (radio). A radio physi- cal media connection is defined as a single radio channel, as e.g. the 30-kHz carrier that is used in TDMA/136, the 200-kHz carrier in GSM, the 5-MHz carrier in WCDMA or a 100-MHz carrier of a satellite transponder. Figure 4.2 shows the symbols to the left. To the right, I modified the physical network from Fig. 4.1 to include a more diversified set of connection types. Each media connection must be specified with resp