ation with private types Private encoding Private encoding algorithm ASPid Abstract syntax. references No private types Encodina algorithm Encodina alaorithm Encoding algorithm SEQUENCE Encoding algorithm BOOLEAN Encoding algorithm INTEGER Fig. 5.51 Handling private types in the message-handling model Summary A logical network represents a partition of a network's total functionality. A logical network is defined by identifying service access points (SAPs) in the C-dimension. Logical nodes are therefore static units in a network that are made visible in, and are removed from, the DC-plane of a network by configuration activities (i.e. not by interactions with network users). For any network concept, the number of logi- cal networks that can be identified by this criteria lies in the range of 5-12 logical networks. A logical network is therefore a rather complex functional entity. Logical networks can be further partitioned into protocol networks. A protocol network performs part of the functionality of a logical network, and therefore also defines part of the functionality of protocols between logical nodes. The protocol networks of a logical network have user-provider (client-sever) relations to each other. These relations are modelled as control service interfaces (CSI) inside logi- cal nodes. This implies that the protocols that are defined within a logical network are independent in the D-dimension. 5 Protocol Network Modelling Protocol elements can have a permanent or a temporary existence in logical nodes. Some protocol elements are common support functions for other protocol elements in the same logical nodes. Such elements are called integrators, and the supported elements are called service elements. Service elements can be further partitioned into integrators and service elements in a recursive fashion. Integrating functions should always be identified and specified separately from service elements, whether or not they are implemented as separate units. An inte- grator is modelled by combining functions