ices that are available over that access. This was not a problem as long as ordinary voice calls were almost the only service used. However, with the advent of IN services in public 3.4 Route Type Examples networks, it became of interest to be able to use one's own service profile, even from other accesses. When I use an access other than my own, I cannot direct the charges to myself (except from pay-phones of course). All these problems arise when the network does not distinguish between the ter- minal user on the one hand, and the terminal and the access on the other (or, in other words, between GTs and NAs). To be able to do that requires technologies for address translation, authentication, and advanced charging methods that could not be implemented before digital accesses and the IN technology were introduced in networks some ten years ago. The ITU-T then quickly defined the network service for universal personal telecommunication (UPT), described in ITU-T F.851. In this standard, UPT is defined as "the ability of a user to access telecommunication services at any terminal on the basis of a personal identifier (i.e. the UPT number), and the capability of the network to provide those services delineated in the user's service profile. Personal mobility involves the network capability to locate the terminal associated with the user for the purpose of addressing, routing and charging of the UPT user's calls." Thus, the UPT number corresponds to a global route between service users, of which at least one is an UPT user. Similar to the case in GSM, however, UPT num- bers are taken from the same numbering system as all other telephony numbers (i.e., ITU-T £.164). Since the network needs to know if a called or calling number is an UPT number, special rules for selecting UPT numbers are defined (see ITU-T E.168). This standard suggests three methods in which .164 numbers may be used to support UPT numbers distinguishing between using the service: only within a single operator network; within a country; international.