 from two supporting generic models: the discrimination model (Sect. 5.3) and the message-handling model (Sect. 5.4). The discrimination model defines discrimination levels, discrimination qualifiers and connection and association handling. The message-handling model defines operation handling (OPH), format handling (FOH), encoding (ENC) and transport service adaption handling (TAH). Message-handling functions that are not made part of the integrator must be handled by service elements themselves. Depending on which message-handling functions are included in an integrator, a protocol between service elements can be characterized as either an abstract protocol, an OSI application protocol or a mes- sage (application) protocol. An abstract protocol is either operation oriented only or service object oriented. An abstract protocol specification is a behaviour description, normally separated into a state machine model for each side of the protocol. An OSI application protocol is an abstract protocol where operation specifica- tions and a message specification are combined into a set of abstract syntaxes, one for each abstract service primitive (ASP) that is defined in the set of operation specifications. A message (application) protocol includes all the previously mentioned infor- mation elements, and, in addition, a set of encoding algorithms. A protocol specifi- cation methodology should include three possible ways of encoding: using ASN. data types, using AML data types and allowing users to define their own private data types. AML supports these approaches by the following techniques: A universal message format for transporting ASPs that are defined according to AML and that use ASN.1 data types. The intelligent message format generator, based on using AML data types. A notation for private data types. Service elements should operate as if the communication service provider (CSP) that services the logical node has almost ideal transport properties. That means that it never corrupts SDUs, it never loses SDUs, it d