ROAMING OF MOBILE DEVICES BETWEEN CELLULAR IP NETWORKS Wellington Albano, Francisco R. Cavalcanti, Rossana Andrade and Emanuel B. Rodrigues Universidade Federal do Ceará, Pós-Graduação em Engenharia Elétrica, Campus do Pici, Bloco 716, 60455-760, Fortaleza, Ceará, Brasil {wellington, rod, rossana}@ufc.br, emanuel@gtel.ufc.br ABSTRACT Nowadays, Internet uses the Internet Protocol version 4 (IPv4) in the network layer. IPv4 assumes that computers are always attached to their networks without the possibility to communicate if they move to a remote location. Mobile IP is an extension to IPv4 that permits the once fixed terminal to “visit” a foreign network and to maintain seamless communication without changing its IP number. However, Mobile IP presents difficulties such as the routing scheme and the need for registration of the mobile terminal with its Home Agent every time it migrates to a new network. Some proposals have been developed that aim to minimize the number of registrations when the mobile terminal is within a limited area. For example, Cellular IP applies mobility management functions of cellular systems within a network domain, but when the mobile device is migrating between two domains, the registration follows Mobile IP. This paper proposes a functional entity to locate mobile terminals when roaming between Cellular IP networks. The cellular infrastructure is used in this proposal to benefit from paging and passive connectivity features that are absent in Mobile IP. KEYWORDS Cellular systems, Cellular IP, mobile systems, Mobile IP, mobility management functions, wireless local area networks. 1 Introduction Mobile devices have the ability to handle Internet services, in environments such as cellular systems and wireless local area networks (WLAN). Cellular systems provide a large coverage area to the mobile users who profit from voice and data communications. On the other hand, in WLANs, mobile devices are connected to a local area network that can offer a direct access to the Internet. In this article, mobility principles from cellular systems are applied to reduce the amount of registrations that are necessary to keep track of a mobile terminal position while the mobile user is roaming between Cellular IP networks. The proposal challenge is to use the benefits of a well-structured cellular infrastructure with well-established roaming agreements among WLANs [1]. The terminal location needs to be determined only when there is data to be received. Likewise, the terminal may be always ready to connect to the network if it needs to transmit without having to establish previous registrations with its home network. Next section shows the main concepts of Mobile IP and Cellular IP that are used in this research. Section 3 introduces a proposal for location registration of mobile devices roaming between Cellular IP networks. Finally, Section 4 presents the main conclusions about our work. 2 Internet Mobility 2.1 Mobile IP RFC 2002 (updated by RFC 3220) presents an extension to IPv4 to support mobility [12][10]. In short, the addition of the following entities gives support to mobility in IPv4 [11]: • Home Agent (HA) is a router in the home network with the following functions: registration of the mobile device when it is away; interception of received data and data delivery through a tunnel to the foreign network. This tunnel may be created, for instance, using IP encapsulation within IP; • Foreign Agent (FA) is a router in the visited network that gives an address to the mobile device and has the function to desencapsulate data sent by the Home Agent. It is also a passive component in the registration procedure, relaying the Mobile Host´s requests to the Home Agent; • Mobile Host (MH) is the terminal visiting a foreign network. In order to communicate properly, it must have an address on the new network. This address is called Care-of Address (CoA) and may be an address of the Foreign Agent or an address externally obtained (e.g., by Dynamic Host Configuration Protocol). In this case, it is called Co-located Care-of Address;