the home to the visited PLMN for local service provisioning. The IN type service CAMEL, customized applications for mobile network enhanced logic, is an example of this. CAMEL is described in Understanding Telecommunications, Book 1. This approach poses some requirements on the home and visited PLMNs: both the visited PLMN and the protocol interface between the visited PLMN and the home PLMN must support the services the mobile station had subscribed to in the home PLMN. If these requirements were not fulfilled, service invocation would not be possible. Roaming subscribers are no longer the exception; they are becoming the norm, which implies that the provision of seamless services for roaming subscribers becomes increas- ingly important. The trend towards universal public network access continues with the globalization of mobile standards and Internet browsers. At the same time, services and content are becoming more personalized and local. Future applications require combined telecom and datacom services. This is combined with the market need to bundle services over different accesses, for example, 'one-stop-shop' and 'one-point-of-care', one bill and one brand. The VHE is a solution in the new situation. The VHE is defined as a concept for per- sonalized service portability across network boundaries and between terminals. The main idea with the VHE is that subscribers are consistently presented with the same personal- ized features, user interface and services, regardless of their access network or terminal (within the capabilities of the terminal). Bundling sets of services forms personalized service portfolios for subscribers belonging to a home environment. The VHE concept is often referred to as 'personalized services for the masses'. The VHE can be implemented with service network solutions. Interconnection Visited Services/Applications Services/Applications Services/Applications Control Control Control- Connectivity Connectivity Connectivity Figure 15.9 Portable services Originating Terminating VISITED V