P/VC levels). By definition, when an NA is the only part of the address parameters of an REdef, a switched route is referred. A destination network address refers a remote node in the hosting network that hosts a node of the hosted network. The hosting network is a switching logical network that contains a switching layer or stratum. Figure 3.24 shows the principle for realizing and using switched routes in a simple datagram-switching network (more or less similar to datagram switching in X.25). Switched route T-ROs T-ROs Switching T-ROs layer This scenario: In T-RE(n21): n22->na2 In T-ROs(n12) na2->n13 In T-ROs(n11): na2->n12 In T-RE(n12): n13->nw01addrPar In T-RE(n11): n12->nw01addrPar Fig. 3.24 Switched routes in a datagram network 3.4 Route Type Examples The difference to link routes is that the node (here n11) that hosts a calling node (n21 here) does not necessarily have a route to the called hosting node (n13 here). The hosting node may have to select a hosting network route that connects to another hosting node that can relay/switch data. In general, both the hosting node at the calling site and intermediate relaying hosting nodes may have several routes that may eventually lead to the called hosting node. This is what requires the host- ing nodes to handle a table that can translate a network address to a route-endpoint identifier (i.e., NA-REi) of the switching network. We denote such tables T-ROs. In Fig. 3.24, the switching network nw1={n11,n12,n13,n14,... hosts the network (nw2={n21,n22,n23,...} nw1 relies on link routes that are realized by two hosting networks, denoted nw01, nw02. The switching network consists of different types of nodes: some nodes both route and terminate (e.g., n11), some terminate only (e.g., n13), and some route only (e.g., n12 and n14). Every node that routes data must include a T-ROs and a T-RE. Nodes that terminate only must know their own network addresses (e.g., na2 for n13) but need no tables. Such nodes are, however, still nodes of the switching network, since the role