nctionality provided by solutions based on IETF Mobility management protocols Subscriber management Billing/Charging radio access Security management network UMTS core network Signalling traffic User traffic Figure 15.21 WLAN as an access to UMTS - related fundamental plans Tight and loose interworking with UMTS Reuse of functionality Other functionality provided by solutions Mobility management based on IETF protocols Subscriber management tight interworking Billing/Charging loose interworking Security management UMTS core network Mobile IP for Internet roaming 'no interworking' Figure 15.22 Different degrees of interworking are possible Many mobile operators consider the SIM card as a way to own the customer, and would like to include the SIM function in the common functions. Another interesting combination is xDSL and WLAN. The end user needs to have two radio interfaces, one for the cellular radio access network and one for WLAN, to benefit from the advantages of complementing cellular access with WLAN. Different deployment alternatives for these two radio interfaces may appear on the marketplace: separated terminals for different radio interfaces and multi- mode terminals, whereby multi-mode terminals integrate both cellular radio interface and Understanding Changing Telecommunications - Building a Successful Telecom Business WLAN into one physical device. In addition to the requirement of having two radio interfaces available, the user subscriber information, which is stored on the USIM, needs to be accessible from both radio interfaces. If there are different deployment alternatives for the two radio interfaces in the marketplace, then naturally there will be different alternatives for providing access to the USIM, based on a single USIM or based on two USIMs. Telecom Management - Operations 'We have to learn to manage the disorder'. . ('Debemos aprender a manejar el desorden'.) Juan Perón 16.1 INTRODUCTION Besides covering telecom management operations at an overview level, this chapter sum- marizes the s