Fig. 2.30 Logical networks exist in the distribution dimension By applying interface refinement on all interfaces between physical nodes, a number of logical networks, related over network service interfaces, will be identi- fied. This structure, the logical node structure, exists in the DC-plane of functional space, as shown in Fig. 2.31. 2.3 Architectural Principles network service interfaces (global SAPs) network interfaces Fig. 2.31 The logical node structures are defined in the DC-plane A logical node structure in the DC-plane is a configuration structure. The model describes the exact configuration of logical nodes in a physical network, since each logical node is identified by a SAP that can be addressed with a SAPI. If we omit the configuration aspect of the model, individual SAPs will disappear, and the whole model can be collapsed to a model in only the C-dimension, where each log- ical network is a single entity. The relations between logical networks now denote types of SAPs, as depicted in Fig. 2.32. logical network logical network network logical network service interfaces logical network (global SAP-types) logical network Fig. 2.32 Logical network structures are defined in the C-dimension only This type of model is called a logical network structure. Note that if the logical node structure is known, the logical network structure can be extracted from all the logical network model fragments that exist in the sysnet model. A logical network structure is therefore a derived model, that is, it is not explicitly part of the set of model fragments that make a sysnet model. It is expected that a tool exists that can browse a sysnet model and extract the logical network structure, either for analysis purposes or for verifying that the sysnet model adheres to an externally created log- ical network structure. The value of the logical network structure is that it describes the complete func- tionality of a network in a distribution-transparent way. In such a model, the func- tion of a logical network is desc