Context transfer for seamless micro-mobility Juan M. Oyoqui and J. Antonio Garcia-Macias {joyoqui,jagm}@cicese.mx Computer Science Dept., CICESE Research Center Ensenada, Baja California, Mexico Abstract Wireless networks and mobile computing technologies are having a profound impact on IP-based networks, as their basic protocols were designed without assuming mo- bility of the network nodes. More recently, protocols like Mobile IP have been designed to handle global mobility, and micro-mobility protocols have been proposed for the management of intra-domain mobility. However, these pro- tocols do not address important issues required for seam- less mobility, such as candidate access router discovery, target access router determination, and context transfer. In this paper, we identify the problems related to seamless mo- bility, underline design considerations to be observed when designing seamless mobility solutions, and propose an ar- chitecture that can be used as a framework for the imple- mentation of these solutions. 1. Introduction Currently, computer networks face important challenges due to the fact that in the early stages of networking all de- vices in the network were considered to be fixed and com- munication protocols were designed accordingly; nowa- days mobile devices are increasingly common and design considerations have to be re-evaluated. The suite of inter- net protocols (IP) is not exempt to this re-evaluation and several problems need to be resolved. One of such prob- lems is related to the fact that the IP address of a node is used to determine its location, so if the node moves within the network it must then change its IP address to be prop- erly located. Mobile IP [13] has dealt with this problem by allowing nodes to change their IP point of attachment (IP- POA) and their IP address within the network. However, Mobile IP has several drawbacks when several handoffs 1 (described below) take place within a domain; this has led to the study of micro-mobility. Thus, usually two types of protocols are used to handle mobility: Mobile IP is used to handle mobility between domains, and a micro-mobility protocol takes care of intra-domain mobility. Among the 1 The terms handoff and handover are used interchangeably in the lit- erature. most important micro-mobility protocols we can cite Hier- archical Mobile IP, Cellular IP, and HAWAII, which will be briefly described later. An interesting problem posed by mobility is context transfer, which arises with the need to minimize the time needed to associate a mobile node (MN) with its new access router. This process is achieved by transferring information about the current state of a MN, known as context, from its previous to its new access router. Thus, an important goal in context transfer is to quickly re- establish in the new access router the context it had in its previous access router; of course, this should be faster, or at least equal, to the case of establishing a new context from the beginning. Context transfer involves deciding which of the potential access routers should be chosen to service the MN; such decision can be based not only on received sig- nal strength but also on the capabilities of the routers and how appropriately they can satisfy needs of the MN. This paper is organized as follows: section 2 intro- duces the problem of mobility in IP-based networks; em- phasis is made on the differences between global mobil- ity, as handled by Mobile IP, an intra-domain mobility, which requires specialized micro-mobility protocols (some of which are presented). Section 3 discusses why seamless mobility requires more than just a mobility protocol, as it involves discovering all access routers that can be candi- dates for becoming the target access router for completing a handoff, some criteria and evaluation methods for select- ing the appropriate target access router, and mechanisms for performing (or attempting to perform) context transfer in order to minimize the impact of handoffs while moving. In section 4 we identify the problems related to seamless mobility, highlighting design considerations that are crucial for the conception of seamless mobility solutions including protocols for candidate access router discovery and context transfer; observing these considerations, we illustrate how our proposed architecture can be used as a framework for the implementation of these solutions. We conclude in sec- tion 5 by summarizing our presentation and then indicate open issues, the scope of our work, and trace the direction for future developments. 1 Proceedings of the Fourth Mexican International Conference on Computer Science (ENC’03) 0-7695-1915-6/03 $17.00 © 2003 IEEE