ng over a CNL-SAP Asynchronous Transfer Mode (ATM) is a standardized CON-CSP that provides packet- switched, transparent connection-oriented connectivity services, to be used for any type of teleservice. It can be regarded as a broadband variant of ISDN. The packets are called cells, and the capacity at user-SAPs is up to 622 Mbps. It is standardized by ITU-T. The recommenda- tions ITU-TI.113, I.121, I.150, I.211, I.321 and I.327 provide an overview of the concept. Pry- cker (1993) has witten a good introductory book, but there are many others as well. 3.2 The Communication Service Provider We now turn to the behavioural aspects of network service interfaces. Both SAPs and CSIs are abstractions of implemented interfaces in the sense that units that are interconnected by CSIs and SAPs communicate by communication events (often referred to just as "events"). Events in network service interfaces are instances of abstract service primitives (ASP). From an event-specification point of view, SAPs and CSIs are, however, very different: All SAPs offer some kind of send and receive operations. These are practically the only types of operations that exist in SAP interfaces. A CSI can comprise any set of operations. Figure 3.19 indicates the type of events that occur in a network service interface of a CON-CSP. connectConRequest(SAPI) sendConRequest(CEI,SDU) provider provider connectConConfirm(CEI) receiveConReportConfirm(CEI,SDU) Fig. 3.19 ASPs in CON-network service interfaces Figure 3.19 gives some understanding of how to use ASPs in logical network modelling. The ASPs in the CON-SAP refer the operations sendCon and receive- Con, the primitive types Request and ReportConfirm and the parameter types CEI and SDU. The ASPs in the CSI refers the operation connectCon, the primitive types Request and Confirm and the parameters SAPI and CEI. The corresponding ASPs for TE-CSP appear as shown in Fig. 3.20. The names of the operations are, in this case, sendInfo, receivelnfo and service. The parameters are SAPI, SIU (service infor