ably more complex. Note that the effect of any separation of layer elements into actors and agents is that actor-actor communication becomes transparent to all communication prob- lems, since agents handle both the messages and the layer interfaces to used con- nectivity services. The only thing a generating actor must do is to deliver the specification of an actor-actor event and a detector address to its agent. Thus, such an event becomes mapped from one AAI to another, as depicted in Fig. 2.16. The actor-actor event "release connection X" is mapped from SCP's AAI to SSP's AAI Layer element A Layer element B actor agent agent actor "map <eventSpec.> on SSP's AAI" Fig. 2.16 The role of agents Some abstract protocols that rely on TCAP are INAP (the abstract protocol between IN actors), MAP (an abstract protocol in GSM), and OMAP (an abstract management protocol in PSTN/ ISDN). 2 Layer Structures Note that agents do not need to know anything of what the actor-actor event is about. Therefore, the actor-agent event (in an AAI) can be conceptually expressed as "map <eventSpecification> on the AAI of <detecting actor address>", as described in Fig. 2.16. This expression is obviously valid for any type of actor- actor event, as long as the actor and the agent have a common language for specify- ing such events and a common system for identifying actors. This fact gives the opportunity to separate the protocol specification between A and B into the three specification components discussed previously. We will discuss these components in detail in the following sections, but separated into connectivity and control lay- ers since there are essential differences as to how AAIs look like and what actors do in these layer types. 2.3.2 Agents and Actors in Control Layers 2.3.2.1 A Case Study We will base this discussion on an analysis of a small part of the DSS1 L3 protocol (part of the call-handling layer depicted in Fig. 2.6), to see how an actor-agent sep- aration affects an OSI RM protocol specification. A protocol defines