he SETUP, but in no way on parameter names in messages, the message format and the encod- ing of parameters, and how the message-handling process deals with its problem. In Fig. 2.18 we have used this insight to simplify the actor description, primarily by removing references to names of SETUP parameters from the description. Note that through the actor-agent separation, the actor part description holds for a variety of modifications of the message protocol (handled by the agent). For example, other parameter names or another set of encoding rules would do as well. If it was necessary to separate SETUP messages into several submessages, it would not bother the actor, as long as the agent reassembles submessages to a complete actor-actor event before contacting the actor. If we read the actor description carefully, it implies that the actor has access to resources that are of no concern to the agent. For example, the actor description implies that it uses some kind of register that defines which services subscribers are subscribed to. It also implies that the actor relies on a register of idle B channels. Other resources that are controlled by the actor in an LE are switching elements, for example. Note, however, that how we describe these resource in a model in no way affects the description in the DSS1 L3 protocol specification of what the actor does. In the OSI RM, resources are not explicitly modeled. In general, however, resources on which an actor relies may be distributed or exist remotely to the actor because they may be used by many other layer elements and layers as well. There must therefore exist special agents and protocols for resource access. For example, let's assume that we allocate subscriber data in a remote database, common for all DSS1 L3 actors in the network. The DSS1 L3 actor may get access to such data over a special resource access protocol, as depicted in Fig. 2.19. Resource access Call-handling-layer element in an LE Subscr. Resource protocol Resource Call-handling DSS1 L3 SETUP agent a