ioning of teleserv- ices between users to a very small and simplified circuit-switched network. This 6 Process Control System Modelling case study gives you an introduction to all the issues one must deal with in service network modelling of PCSs: resource system modelling, service network model- ling, operation specification and behaviour specification. Note that, although we take a teleservice network as an example, the same modelling principles can be used for any kind of processing system We will introduce the complete formal notations for resource system modelling and for behaviour descriptions in Chap. 7. This example is discussed using intui- tive notations to some extent. Most of the concepts that are used in service network modelling are also introduced in this case study. A more thorough analysis of con- cepts is, however, also left to Chap. 7. 6.2.2 Service Resource Modelling The resource system for providing teleservices and connections between users is depicted in Fig. 6.5. Connection users are CNUs, teleservice users are TEUs. The model is drawn in a domain-specific notation. unused unused 66..1920 35. 1920 x 35 6 switch route 5 36 65 access routes internal route Fig. 6.5 The resource system drawn in a domain-specific notation The model shows a circuit-switched network that connects ISDN-type accesses as well as single-channel digital and analogue accesses. The network includes two circuit switches (SW1 and SW2), seven connection users (CNU1 trough CNU7) and eight routes (AR1 through AR6, SR1 and IR1). The connection users are teleservice resources (TE-UDTs and TRs) that are instantiated in CNUs in terminal systems (CNU1 through CNU6) and inside the operator network (CNU7). TEUs are connected to TE-UDTs over TE-SAPs. The switches are interconnected over a switch route that comprises thirty 64- kbps channels. A CNU in a terminal system has one access route to a switch. Access routes are either ISDN-type accesses (only 2x64 kbps is assumed) or single-channel routes. The latter might be either analogue