 of a switched logical network is to route, originate, and terminate. In AMLn, every layer terminates data in terminating nodes. A switching logical network definition therefore always includes the logical nodes where data are ter- minated, even when such nodes do not perform any routing function. In imple- menters' descriptions, however, terminating nodes are often regarded as existing externally to the "network," i.e., they are not regarded as parts of the switching layer or network. This is because implementers tend to use a closed, vertical parti- tioning view on networks. From an operational point of view this makes sense: ter- minating logical nodes exist in terminal equipments that are normally not operated by operators. Operator network parts on the one hand and terminal equipment on the other may also be supplied by different suppliers. These aspects are irrelevant, however, when modeling switching layers and logical nodes of network systems, where an open view on switching networks should be applied. Let's now look at the network address (NA) that is used for switched routes: the model in Fig. 3.24 indicates that every node in the switching network that hosts nodes must also have and know its own network address (na1 for node n11 and na2 for node n13). However, the depicted scenario also indicates that it would work equally well if the hosting node name n13 had been used instead of the network address na2. So, why do we use two different parameters for the same thing? There are at least three good reasons: 1. Similar to the network in Fig. 3.24, most public switching networks contain many switching, multiplexing, and relaying nodes that do not host any nodes, but need to be identified by their node names in the T-ROs and a T-RE tables of the switching network. Thus, network addresses only refer the subset of hosting nodes that must be known by hosted nodes. This subset and how to identify it is defined by the numbering system of the switching network. 3 Node Structures 2. If a hosted node is moved to an