4.22 for this discussion (compare with Fig. 4.20). Terminal System internal interface Global user generateEventORDER detectedEventC_REPORT A-EVH A-MEH Logical platform global SAP global send & receive global SDUs Logical B -MEH B-EVH local SAP Global provider - local send & receive - local SDUs Fig. 4.22 Mapping a global SAP on local SAPs 4 Physical Network Modelling The model in Fig. 4.22 shows a terminal system in both a global and a local view. There are two logical nodes that communicate with an operator network (not shown), using global message protocols PR1 and PR2. These logical nodes are allocated in two different physical nodes (global user and provider) inside the terminal system. The network interface between these physical nodes includes the global network service interface, i.e. a network service interface in the func- tional space that defines the terminal system and the operator network. It is assumed that the global network service interface is a CNL-SAP (However, the following discussion is not restricted to this type of network service interface.) The operations that are defined over the global SAP are global send and receive operations. Each logical node is implemented in an application on the node platform. Each application consists of an EVH (that implements the global logical node) and a message handler (MEH) that interfaces the node platform and the local message protocol for communication between the two physical nodes. The interesting part of the node platform is the connectivity service it provides (which is modelled as a CSP) for communication inside the terminal system. This CSP could be an internal IP network (i.e. a LAN) for communication between different physical nodes inside a terminal system, which is a rather common method to implement a physical node as a distributed system. The local SAP type is assumed to be a CNL-SAP. Local SAPs can be used for anything, but in this discussion we are in this discussion only interested in their use for supporting communication over the global