etwork RP1 definition: Route type is: IP operator Route type is: LAPD Protocol is: SNMP Protocol is: Q.931 Route id.: IP addresses Route id.: SAPIO controller RP4 definition: Route type is: SCCP user-user RP2 definition: Protocol is: INAP/TCAP messages Route type is: SCCP Route id.: Global titles Protocol is: ISUP Route id.: DPC+SSN Fig. 3.97 Using reference points to simplify logical network models 3 Logical Network Modelling In the complete generic model, we include only one logical node of each type, see Fig. 3.98. If there are constraints, such as how many TPCs a SAF can connect or how many SSFs an SCP can handle, the model is annotated by these numbers. Network operator controller ISDN Network Process user-user messages Controller N Number of LAPD links a SAF can handle M Number of SSFs a SCF can handle Fig. 3.98 The generic logical network model This model can now be used for creating instances of logical networks with a specific number of logical nodes of each type and with instantiated reference points. To instantiate a reference point implies allocating values of the address attribute of each route endpoint for each reference point instance. The logical net- work is thereby configured in relation to the CSPs that are used for transporting messages (the SCCP, the LAPD and the X.25/IP). Figure 3.99 is an example of such an instantiation (interfaces to resource controllers are omitted). Lower-case letters denote node and reference point instances. External networks Fig. 3.99 An instantiation of the generic model 3.6 Summary This logical network contains four SAFs, two SSFs, two STFs, one SCF, one SMF and no SDF. There are three routes that interconnect this network to other net- works. The network is, in its present form, designed for handling 190 000 accesses. Summary The key concepts discussed in this chapter are the logical network, the logical net- work structure and the communication service provider (CSP). In relation to func- tional space, these concepts and all modelling examples shown, were strictl