guided by the generic logical network structure in Fig. 3.91. The charging-network protocol network (CHN) has protocol elements in MS, MSC, GMSC, SMS-GMCS and OSS. CHN is a support network to SH. The service-handling protocol network, SH, uses the service of BRO, COH, HO, PAG and CHN. SH controls the establishment of teleservice connectivity over the GSM network, such as connectivity for voice calls, data calls, short messages and voice messages. SH can also ask CHN for the costs of an ongoing call and deliver that information to the MS. SH has protocol elements in MS, MSC and GMCS. The protocol networks discussed here are all parts of the GSM process control system (GSM-PCS). They are all related through network service interfaces of 5 Protocol Network Modelling type CSI, since they use and provide services to each other. Consequently, we can describe these relations in a protocol network structure for the GSM-PCS, similar to the logical network structure that was discussed in Sect. 3.5.4. Figure 5.8 shows this structure. GSM-PCS logical network, protocol network structure Charging Call handling Equipment control (CHN) (EIC) Mobility Authentication & Paging Service handling control (PAG) ciphering Handover Registration (REG) Service access Roaming Locating handling (SAC) (ROA) (LOC) Connection Handling Broadcasting (COH) Other (BRO) integration functions Fig. 5.8 The protocol network structure for the GSM-PCS The structure contains the 11 protocol networks that have been discussed. Some of the protocol networks are also aggregated into call-handling and mobility con- trol networks. The rationale for this is that mobility control functions represent the primary difference between networks that support mobile (cellular) accesses and networks that support fixed accesses. The remaining parts of the structure are iden- tified as independent of the type of network access. The GSM-PCS logical network must also include integration mechanisms. For call-handling support, there exists a special integration mechanism, here 