Two user location strategies for personal communications services

The vision of nomadic personal communications is the ubiquitous availability of services to facilitate the exchange of information between nomadic end users independent of time, location, on access arrangements. To realize this, it is necessary to locate users who move from place to place. The strategies commonly proposed are two-level hierarchical strategies, which maintain a system of home and visited databases/spl mdash/home location register (HLR) and visitor location register (VLR)/spl mdash/to keep track of user locations. Two standards exist for carrying out two-level hierarchical strategies using HLRs and VLRs. The standard commonly used in North America is the Electronics Industry Association/Telecommunications Industry Association (EIA/TIA) Interim Standard 41 (IS-41), and in Europe the Global System for Mobile Communications (GSM). The authors introduce these two strategies for locating users and provide a tutorial on their usage. Different forms of mobility in the context of PCS and a reference model for a PCS architecture are discussed. The user location strategies specified in the IS-41 and GSM standards are described, and then, using a simple example, a simplified analysis of the database loads generated by each strategy is presented. Also briefly discussed are possible modifications to these protocols that are likely to result in significant benefits by reducing query and update rate to databases and/or reducing the signaling traffic.<>