 needed: the r-invokeOrder and the -invokeReport (r- invOrd and I-invRep for short), see Fig. 2.27. Since these primitives are associated with control layers only, we refer to them as the primitives of a specified agent interface (SAG). Using-layer element Layer element I-invRep(...) Agent Message protocol Actor r-invOrd(...) Used layer element Fig. 2.27 Meta-primitives in a specified agent interfaces (SAG) carry LSM primitive information 2 Layer Structures The r-invokeOrder(...) is used by an actor to invoke its agent in order to invoke a remote actor with an LSM-event. The I-invokeOrder(...) is used by an agent to invoke a local actor in order to make it act on an LSM event that was generated by a remote actor. The parameter field of these meta-primitives are identical and are (more or less) given by the general message format in Fig. 2.26, which means it consists of all or some of the following parameters: detector reference (optional), invocation identifier (optional), object identifier (optional), operation name, primitive type and ASP parameters. A more detailed and formal specification of these meta-primitives is given in Appendix B. To model a SAG when specifying control layer protocols is always an excellent conceptual tool for making such specifications reasonably small and intelligible. It does not, however, mean that SAGs must be standardized. It all depends on what purpose we intend to use it for: 1. An obvious and very important purpose (considering how standards are written today) is to use it for simplifying the specification of an OSI layer, as described previously. If that is the only objective there is no need to standardize SAG primitives, which implies that they will be realized by each implementor in his or her own way. An implementor who separates actors and agents in different modules may choose to use some local message passing mechanism for communication over SAGs. In that case, different local messages will be defined to represent the two invoke types, or an operational approach may be 