inal side network side End-users Network Terminations Terminal Teleservice Access Protocol Process Local Controller service control Resource Resource control control Telecom User-data Controller Resource Network control Termination (TRC) Process Operator Controll. TE-UDT \Teleservice protocol TE-SAP TE-UDT TE-TPC Processing Process Control System Processing system system users Resource System operators Control information NPC Network Process Controller TPC Terminal Process Controller remote local SAP Service Access Point TR Telecom Resource TE Teleservice TRC TR Controller User-data flows TEC TE Controller UDT User-Data Termination TEU TE User remote local Fig. 2.1 A logical model of a telecom system In addition to the logical structure, Fig. 2.1 also shows the mapping of functional entities, so-called logical nodes, on the processing system terminology (at the bot- tom) and the telecom terminology (at the top). We will discuss this model in terms of the structural aspects it shows: implied physical separation, functional separa- 2 Foundations of Sysnet Modelling tion, interface types and teleservice users services access points (TE-SAP): Implied physical separation: Some entities belong to the network side, others to the terminal side. This almost always implies a physical separation between entities on respectively side. One type of physical interface is removed in comparison to Fig. 1.8: the M/E interfaces between resources and sensors/effectors. These interfaces are col- lapsed in the model, since in sysnet modelling we cannot deal with matter and energy interfaces. We will instead regard as a telecom resource (TR) an entity that provides two things: it provides input and/or output user-data flows, and it can exchange control information with its telecom resource controller (TRC). The network side of the resource system is built by many telecom resources, some of which are physically separated. Since teleservice users (TEU) do not communicate with entities on the net- work side, entities on the network side c