ider cannot be used to model common service providers in public networks like teleservice, transmission and transport networks. Most SAPs in these net- works have no SAPIs and in transport networks, the CSIs are not available to users. OSI RM did not define symbols for network service interfaces. In AML, there is a rich set of symbols for different types of interfaces. The model in Fig. 3.7 The CSI symbol is a general interface symbol. It can be used to denote an interface where a user requests connectivity services from a CSP. It can also be used by a distributed process control system to request something from a resource controller, or by a network process controller to request some information from another logical node in the process control system. 3 Logical Network Modelling shows three different symbols: the SAP symbol for teleservices, the SAP sym- bol for connection-oriented packet-switched services and the CSI symbol. The effort that led to the OSI RM in 1984 produced an admirable result. It also drew the attention of many systems architects. It led to many valuable insights in the architecture of communication systems and presented some good architectural concepts. The OSI RM is, however, constrained to packet switching networks and deals basically only with the architecture of terminal systems. The difference between SM&AML and OSI RM are mainly due to the fact that the OSI RM context was a packet-switched data communication services. Several concepts that OSI RM defined are reused in SM&AML within that context, such as the service access point identifier (SAPI), the abstract service primitive (ASP7) and the connection endpoint identifier (CEI). In order to understand the relative com- plexity of the CSP in SM&AML, a brief overview of how the OSI service provider concept was developed may help. Figure 3.8 shows the OSI RM understanding of a service provider in 1984. 1984 OSI Service provider: ASPs in the interface: CONNECT request User protocol CONNECT indication CONNECT response CONNECT confirm RESET 