access point Point-to-point identifier Broadcast Point-to-point. Protocol "Protocol" refers e.g. IP and other networks Point-to-point, several channel rates Cross-connect Point-to-point, several channel rates BRA/PRA Point-to-multipoint of D and B channels *) Networks that use NA are switching networks **) Discrimination is by position ) Domain names (a kind of GT) are supported by DNS Fig. 3.9 Addressing parameters defined by different network systems These are all good reasons to modify nw1 to a logical-network structure instead. In Fig. 3.10 we have re-defined nw1 as a common hosting logical network. Two hosted networks are shown, nw2 and nw3. The nw1 model tells us that it is hosted in three logical networks, nw01, nw02, and nw03, which are not shown here, how- ever. 3 Node Structures 11133 Fig. 3.10 nw1 is a hosting network for nw2 and nw3 The information given by these models tells, through different route symbols (read more about this in Sect. 3.3), which type of connectivity service a particular logical node must rely on. The annotations on these symbols identify the hosting logical networks (e.g., the route between n13 and n14 is created through the logical network nw03). This information is the part of the logical network dimension (NW) that is not dependent on the exact configuration of hosted nodes in hosting nodes. It is therefore a relatively stable form of information of the model. We can refine these models to define the configuration of logical nodes in a particular net- work by adding hosts relations between nodes of different logical networks, which is the more volatile part of the NW dimension. Figure 3.11 shows several ways in which this information can be specified. hosts Logical-network structure table: Hosting node Hosted nodes Fig. 3.11 Different methods to define hosts relations, i.e., logical network structures 3.2 Logical Networks At the top we have refined network nw1 with graphical hosts relations. Note that a logical node (e.g. n11) can be hosted by nodes of several other networks. 