lements are related to the functional content. An optimal solution offers an acceptable service at lowest cost. In Chapter 5 the expression 'Economy of service' is introduced. This service production view is further developed in Chapter 8 for a packet production assembly line. Finally there is a need for an interconnection plan. Such plan is very similar to a set of fundamental technical plans. Critical interconnection issues, at least for fixed opera- tors, are: Point of interconnect (POI) Services Subscriber access Number portability Charges and payments Billing Numbering Signalling and interface standards Routing principles (e.g. emergency) Synchronization Installation, operation and maintenance QoS and security Service level agreements The interconnect area is treated in more detail in Chapter 15. Another kind of interconnect is represented by cooperating technologies, such as UMTS and WLAN. Three possible relations are shown in Figure 3.29. Tight interworking means Other functionality provided by solutions Mobility management based on IETF protocols Subscriber management Tight interworking Billing/Charging Loose interworking Security management UMTS core NetworkSe Mobile IP for Internet roaming "No interworking" Figure 3.28 Technical interworking Networks and Technologies Marketing expenses, Competitors Business Pricing Total market (all users) User needs Revenue User segments Market share, churn (regulations) Service offerings Operating expenses Other operators and service providers Financial calculations Interconnect ROCE, NPV ROI, Risk Investments Network Accounting Figure 3.29 The multi-operator environment also requires an interconnect plan which embraces many of the other plans, such as routing, QoS and numbering that UMTS provides the functions for both systems. Loose interworking means that the technologies work more autonomously. For the new generation network the following list gives examples of further plans under review: Technical framework/Network modelling Traffic handling Call processing Servi