the modelling of the resource system part of telecommunication networks in spe- cific. Modelling a process control system is based on creating a model of the resource system, called the resource system model, and partitioning that model according to an abstraction hierarchy for the process control system. SM&AML is interface-oriented. Contrary to most other modelling methods, collaboration structures that are created through sysnet modelling are based on interfaces and relations between interfaces. Collaboration structures based on units are derived from the interface-oriented structures. Sysnet modelling defines the relation between these two views on structures as the dualism between interface and unit. 2.7 Summary The basic separation of concerns in sysnet modelling is that the functionality of a physical node is separated into a node platform and into functions that are visible on the level of a physical network, the so-called node network function (NNF). The separation between node platform and NNF identifies the processing dimension A NNF can handle several network interfaces. Each network interface can be disintegrated into a hierarchical discrimination structure of logical nodes in physi- cal nodes by introducing service access points (SAP) and suitable platforms. Dis- crimination structures of logical nodes represent the communication dimension (C). Logical nodes in different physical nodes that can communicate according to a mutually agreed protocol are part of the same logical network. Such logical nodes are said to exist in the distribution dimension (D). The three dimensions, D, P and C, are referred to as functional space. Each physical network level defines its own functional space. Between physical network levels, global SAPs of the higher level are mapped on network interfaces on the lower level, and local SAPs of the higher level become global SAPs on the lower level. The disintegration principle can be recursively applied: a protocol can be recur- sively disintegrated. On each level, a protocol