matic summary of all the kinds of units we have used in resource systems modelling in this chapter. Section 3.5.3 summarizes the units we have used for modelling the process control system of CSPs. In Sect. 3.5.4 we discuss how the logical network structure of CSPs can be modelled in a systematic way. In Sect. 3.5.5 a compact notation for logical network modelling is suggested. 3.5.2 Units in Resource System Modelling, Summary These units have in common that they take part in providing connectivity serv- ices over SAPs. Some of them are controlled over CSIs. If we disregard the differ- ent variants of physical media, switches and types of CSPs, there are, in all, only five types of primitive units: physical media connection, multiplexer, switch, user- data termination and SAP-users. Of these units, only the user-data termination ter- minates protocols. To support the expressiveness of logical network modelling, AML defines some symbols for interfaces and annotations in resource system models. These are sum- marized in Fig. 3.83. Note that there are a number of specializations for SAP sym- bols and CSI symbols that were discussed in Sect. 3.2.4. Specializations for physical media are first discussed in Chap. 4. 3 Logical Network Modelling Symbol Acronym Physical media connection (example) User-data protocol (many alternatives) Connectivity domain (represents everything in a model that can be accessed over a single SAP) Service access point (example) Control service interface (example) Multiplexer annotation Digital cross-connect switch annotation CN or CS Circuit switch annotation Connection-oriented packet switch annotation Connection-less packet switch annotation Fig. 3.83 Symbols and annotations for primitive units in resource system modelling We have also seen that physical networks are built by using different kinds of CSPs and logical networks in a structure of logical networks, see Fig. 3.12. To sup- port the identification of which type of unit you see in a model, suitable generic prefixes have been sugges