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Fundamental Challenges in Mobile Computing M. Satyanarayanan School of Computer Science Carnegie Mellon University Abstract This paper is an answer to the question: "What is unique and conceptually different about mobile computing?" The paper begins by describing a set of constraints intrinsic to mobile computing, and examining the impact of these constraints on the design of distributed systems. Next, it summarizes the key results of the Coda and Odyssey systems. Finally, it describes the research opportunities in five important topics relevant to mobile computing: caching metrics, semantic callbacks and validators, resource revocation, analysis of adaptation, and global estimation from local observations. 1. Introduction • Mobility is inherently hazardous. A Wall Street stockbroker is more likely to be What is really different about mobile computing? The mugged on the streets of Manhattan and have his computers are smaller and bits travel by wireless rather laptop stolen than to have his workstation in a than Ethernet. How can this possibly make any difference? locked office be physically subverted. In addition to Isn’t a mobile system merely a special case of a distributed security concerns, portable computers are more system? Are there any new and deep issues to be vulnerable to loss or damage. investigated, or is mobile computing just the latest fad? • Mobile connectivity is highly variable in This paper is my attempt to answer these questions. The performance and reliability. paper is in three parts: a characterization of the essence of Some buildings may offer reliable, high-bandwidth mobile computing; a brief summary of results obtained by wireless connectivity while others may only offer my research group in the context of the Coda and Odyssey low-bandwidth connectivity. Outdoors, a mobile systems; and a guided tour of fertile research topics client may have to rely on a low-bandwidth wireless awaiting investigation. Think of this paper as a report from...