1 MCK: Wireless Communication with Mobile Agents. Authors: Leon Hurst, Trinity College Dublin, Dublin 2. Fergal Somers, Broadcom Éireann Research Ltd., Dublin 2. Pádraig Cunningham, Trinity College Dublin, Dublin 2. In mobile computing, a computer which in 1970 filled several large rooms, has been reduced in size so that it is now slips neatly into your pocket or is bound to your wrist. It has taken the last decade for this feat of engineering to come to fruition. Meanwhile, we have also experienced many evolutions and revolutions in the software systems and communication fields. The most dramatic of these is the unprecedented rise of the Internet and large Intranets. Key to this revolution is the great need which people have for ubiquitous and instant communication. Hence, a fundamental question which Computer Science is asking itself is: “How do we support complex communication-based applications on our now sophisticated, yet limited, mobile computing devices?” Initial answers to this question range from the infrastructure-level (e.g. GSM which offers ~1Kbps maximum bandwidth [3]), to the system level (e.g. PPP and TCP/IP), up to the application level (e.g. Lotus cc:Mail and Lotus Notes). In order to tackle part of this question we concentrated on the mismatch between conventional communication protocols (e.g. TCP/IP) and the hostile characteristics of cellular wireless communication networks (e.g. GSM). To this end we have developed the Mobile Communication Kernel (MCK). The cellular wireless environment is deemed hostile as it suffers from device mobility, frequent and prolonged disconnections, very low variable bandwidth and high latencies. A Mismatch of two Technologies Communication-based applications (e.g. email, WWW, Lotus Notes) were developed when communication systems were based on fixed networks and powerful desktop computers. Little thought was given to their performance in a mobile computing context. Thus, we find ourselves today with distributed applications running over fixed network-based protocols in a mobile environment. These protocols are based on a set of assumptions related to wired networks which are false in the wireless case (see sidebar: Limitations of Conventional Protocols). The assumptions are presented in the second column of Table 1. Table 1. Comparison of attributes of a fixed network with a celluler mobile network. Network Attribute fixed network-Internet cellular network-GSM Location (logical/geographical) Both fixed variable/mobile Connection life-time long-lived (years) short-lived (minutes) Bandwidth ~64Kbps-Gbps maximum of ~10Kbps Latency mostly <300 msec >1 second Reliability very high very low Rate of change of topology very slow (over months) very fast (over seconds) Power of end-point devices Powerful desktop PCs and workstations Limited PDAs or laptops, physically vulnerable However, a mobile computing and communication system is characterised by very different characteristics [5, 6] as presented in the third column of Table 1. The important characteristics of the mobile communication environment (third column) are essentially the opposite of the characteristics assumed in the development of conventional communication protocols (second column). The characteristics of a cellular wireless network fluctuates wildly while those of a fixed network changes slowly over time. Therefore, protocols such as TCP, RPC and CORBA method invocation (essentially RPC) suffer a variety of