represented (in the C-dimension). After applying this disintegration step on all net- work interfaces of a physical network, many different logical networks have been identified, each covering a special domain of the network. The set of all these logi- cal networks and nodes gives the complete picture of the physical network in the DC-plane. When all parts of the NNF have been allocated to platform service inter- faces as well, we have the complete picture of the physical network in functional space. Logical network modelling is discussed in Chap. 3, physical network modelling in Chap. 4. Disintegration step 2, logical networks -> protocol networks: The second disintegration step further disintegrates a protocol between logical nodes into separate message protocols that are handled by units called protocol ele- ments, see Fig. 2.49. 2 Foundations of Sysnet Modelling global SAP Protocol element, global SAP disintegration step 2 Protocol element Service Association Logical element endpoint Association global SAP integration step 3 Integrator permanent temporary discrimination D-dimension view protocol global SAP Fig. 2.49 Disintegration: logical node -> protocol element As in the case for NNFs and logical nodes, protocol elements also have an exist- ence in all three dimensions. Note that, when viewed in the C-dimension alone, protocol elements are called service elements. One of the protocols may be an association and discrimination protocol. The unit that handles this protocol is a permanent unit in the logical node, called the integrator. Other protocol elements have a possibly temporary existence in the logical node. A logical node can be the "host" for many protocol elements simultaneously. A protocol element only exists in the C-dimension if it is connected to the integrator in the C-dimension over association endpoints. Each endpoint represents a logical sub-flow of the data flow over the global SAP. The internal structure of the logical node in Fig. 2.49 shows discrimination of data flows on one level only.