-ROs Packet common handling (PH) SAG agent layer stratum Media Media Other agent actor resources MTP L3 stratum MTP L2 agent layer X. and V. SDH path Alternative ways Switching control actor to provide actor layer agent layer connectivity for MTP L2 mux layer SDH cross- connect or mux actor (agent layer Fig. 1.38 The L dimension consists of several subdimensions, one for control structures (Lac) and several for connectivity structures (Lco) By applying a structure in the N dimension on the ISDN call-handling layer, for example, we can model its LPM and LSM separately in the L-N plane. Figure 1.39 shows a possible LPM. TCAP common agent layer DSSI L3 DSS1 L3 agent layer ISUP agent layer SCCP MTP L3 TE TE LE/SSP TE TE Fig. 1.39 The LPM for an ISDN call-handling layer. LE=local exchange; SCP=service control point; SSP=service switching point; TE=terminal; TR=transit exchange; TU=terminal user 1 Introduction to Network System Modeling The assumed structure consists of terminals (TE), local exchanges (LE), etc. The corresponding LSM looks as in Fig. 1.40. Note that since it consists of element state machines (ESM) that reside in actors only, this model exists in the LAC-N plane only. SCP resources T-ROs TE resources TE resources all /DSS1 L3/ all/DSS1 L3/ T-ROs all /ISUP/ T-ROs TE resources LE/SSP resources: LE resources TE resources - Subscriber data manager - Switching machine TR resources - B-channel manager - Etc. LE/SSP SCP TE TE Fig. 1.40 the LSM that corresponds to Fig. 1.39. T-ROs=routing table The node dimension (N) resolves into a logical node dimension (NO) and a log- ical network dimension (NW) when a network system is horizontally partitioned into a logical-network structure. For example, if we choose not to do SO in the IP- network case discussed in Sect 1.4.3, we would describe the system as a single log- ical network, as depicted in Fig. 1.41. d Local DNS server D Remote DNS server H Host R Router Fig. 1.41 A network described as a single logical network exist in the N dimension The nodes in this model