cal networks are con- figured in relation to each other. To be able to operate logical networks independ- ently, the following requirements must be fulfilled: Hosted nodes must be defined as packages that do not reveal their layer element contents. Layer interfaces to be used by hosted nodes must have a standardized realiza- tion. A hosting logical node must support multiple layer interfaces for hosted nodes. It must be possible to bind a hosted node to a layer interface, offered by a host- ing node, through a configuration activity from the management system. Let's therefore look at how a hosting logical node must be designed. The generic model in Fig. 1.29 defines all concepts that are associated to logical network struc- tures. Hosting node Hosted node Layer Route element endpoint Switched route Config. tables Manag. system Config. Layer(-s) that define the tables Link route hosting logical network Fig. 1.29 Concepts that define logical network structures A hosting node contains a functional element that must be able to support changeable contents of multiple hosted nodes. It may also be a hosted node in one or several hosting nodes. The functional element may be a single layer ele- ment (as in Fig. 1.29) or a layer structure. Since the contents of hosted nodes is changeable, it must be defined by data in configuration tables that are maintained from a management system. This con- figuration function relies on the hosts relations, defined in the logical-network structure model. A logical node communicates with peer nodes over routes. The node knows the route endpoint to each peer. A route endpoint can be the name of a remote node 1 Introduction to Network System Modeling and such names are only locally known within the very logical network (some- times called "global titles"). Some hosting networks support global titles (GT). Most hosting networks do not, however. A hosted node must therefore also include configuration tables that relate route endpoints to address parameters to be used in the layer interface t