col machine (LPM): State-machine handler (SH) Message protocol Fig. 1.18 Layer state machines and layer protocol machines are parts of the same control layer. An ESM also controls all resources on which the layer relies, in the node in which the ESM resides. The separation of a control layer into one or several LSMs and an LPM implies that we must define ESM_in relations in the model. We also get two views on actors: when we talk about actors in the LSM context, we refer an ESM, while in the LPM context it is a state-machine handler (SH). 1 Introduction to Network System Modeling An SH will communicate with its agent by events as well. These events carry the ESM events. AMLn defines them as meta-primitives (see Fig. 1.19). LSM event ESM_in ESM_in State-machine handler (SH) Message Meta primitive is: Meta primitive is: r-invokeOrder(ESMidentity, LSMevent) I-invokeOrder(ESMidentity, LSMevent) Message that encodes every element of the meta-primitive Fig. 1.19 Primitives in actor-agent interfaces of control layers are meta-primitives One meta-primitive is the r-invokeOrder(...), the other is the HinvokeOrder(...). Every actor-agent interface of a control layer can be specified by using these two primitives (or some user-defined specialization of them). Figure 1.19 shows the simplest form of meta-primitives (AMLn defines a few more parameters, see Appendix B). The introduction of meta-primitives explains the role of the LPM as a "carrier" of LSM events, i.e., to encode every information element of a meta-primitive into some message format. As a result, an LSM event that is defined by an r-invoke in one actor-agent interface will be reproduced by an I-invoke in another, which implies that an LPM maps an abstract protocol on a message protocol. The LSM-LPM separation principle has a very simplifying effect on the com- plexity of some protocol specifications. Since an OSI RM protocol for a control layer does not apply the actor-agent distinction, its state machine can become very complex, if its states are defined by mul