rotocol network may represent a network transaction (i.e., have a limited lifetime in the DC-plane of functional space). However, it may also represent a permanent function in the DC-plane, in case no association and discrimination protocol is defined for the corresponding logical network. Protocol network modelling is discussed in Chap. 5. Disintegration step 3, protocol networks -> abstract networks: The third disintegration step separates a message protocol in a protocol network into two permanent parts, representing the form and the meaning of the communi- cation. The form is defined in a message handling protocol and the meaning in an abstract protocol. The message handling protocol consists of the rules for message formatting, encoding of message data, message error control and a number of other message handling functions. The abstract protocol describes communication between the protocol elements in a highly abstract language, where protocol ele- ments interact by communication events that request "operations" and provide "responses" and spontaneous "reports". As a result, the function of a service element is separated into two units, one called message handler (MEH) and one called event handler (EVH), as depicted by Fig. 2.50. The MEH is the integration mechanism in this case. In Fig. 2.50, a serv- ice element is taken as an example, but the same principle can be applied to integra- tors. Abstract machine Protocol element disintegration step 3 abstract Event protocol Handler Service event element message interface Association handling Message endpoints Handler integration step 2 protocol Fig. 2.50 Disintegration: protocol element -> message and event handlers Communication events in an abstract protocol are instances of abstract service primitives (ASP), as e.g. connectPortRequest(SAPI,SAPI) or the connectPortCon- firm(-). Communication events express the core functionality in a protocol network, since message handling is just an integration mechanism that should handle all events in the same way. 2 Found