nw1.2)}. T-RE(n1.4.1): n1.4.2->(NA(nw1.2), APi(nw1.2)}. T-AP(n1.2.1): ap1->nw1.3; ap2->nw1.4. Fig. 4.11 Logical networks and nodes on network level 1 For the sake of this discussion, we name logical networks after the network level on which they are defined (e.g., nw1.1 is defined on network level 1 and has the network number 1). Consequently, the node n1.2.1 is a node on network level 1 of network 2 and has the node name 1 within that network. We assume here that layer element A is part of a switching layer. The hosting node n1.2.1 is a terminating node of the switching logical network nw1.2 that real- izes socket routes for nodes of nw1 1.3 and nw1.4. As usual, the hosted nodes n1.3.1 and n1.4.1 handle T-RE tables that provide relevant address parameters of nw 1.2. Layer element A in n1.2.1 handles a T-AP table that relates APi values to network identifiers of hosted networks (assuming that n1.2.1 hosts only one node per hosted network). So far there has been nothing new. Let's now realize the layer interfaces of this model as network interfaces, i.e., comprising routes and interlayer protocols. This 4 Modeling Vertical and Horizontal Partitions implies that we introduce a completely new view of logical networks and nodes on network level 2 (see Fig. 4.12). n2.1.3 n2.2.3 nw2.1 nw1.2 n1.2.1 n2.1.2 n2.2.2 n2.1.4 nw2.1 nw2.1 nw1.2 {data, nw1.2originator) n1.2.2 n2.2.1 E (nw1.1) n2.1.5 ..,ap1,...} nw2.1 nw2.1 nw2.1/nw1.2 nw1.2 n2.1.1 E (nw1.1) Fig. 4.12 The network level 2 view of a horizontally-partitioned network level 1 node This view is only defined inside node n1.2.1, i.e., it is not visible from any other network level 1 node. We therefore say that this node structure is orthogonal to the node structure on network level 1. We have assumed that the network level 2 view inside n1.2.1 comprises a switching network nw2.1 (e.g., a LAN) that is a hosting network for, e.g., an internal network nw2.2. This network realizes the network level 1 node n1.2.1 by including each of the layer elements A', B' and C' in an nw2