There is general belief that networks based on wireless technologies have much higher error rates than those based on more traditional technologies such as optical fiber, coaxial cable, or twisted pair wiring. This difference has motivated research on new protocol suites specifically for wireless networks. While the error characteristics of wired networks have been well documented, less experimental data is available for wireless LANs. In this

The ability to access information on demand when mobile will be a critical capability in the 21st century. In this paper, we examine the fundamental forces at work in mobile computing systems and explain how they constrain the problem of mobile information access. From these constraints, we derive the importance of adaptivity as a crucial requirement of mobile clients. We then develop a taxonomy of adaptation strategies, and summarize our research in application-transparent and application-aware adaptation in the Coda and Odyssey systems respectively.

Office delivery robots have to perform many tasks. They have to determine the order in which to visit ofces, plan paths to those offices, follow paths reliably, and avoid static and dynamic obstacles in the process. Reliability and efficiency are key issues in the design of such autonomous robot systems. They must deal reliably with noisy sensors and actuators and with incomplete knowledge of the environment. They must also act efficiently, in real time, to deal with dynamic situations. Our architecture is composed of four abstraction layers: obstacle avoidance, navigation, path planning, and task scheduling. The layers are independent, communicating processes that are always active, processing sensory data and status information to update their decisions and actions. A version of our robot architecture has been in nearly daily use in our building since December 1995. As of July 1996, the robot has traveled more than 75 kilometers in service of over 1800 navigation requests that were specified using our World Wide Web interface.

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Zhu, Senior Member, IEEE Roaming across heterogeneous wireless networks such as wireless wide area network (WWAN) and wireless local area network (WLAN) poses considerable challenges, as it is usually difficult to maintain the existing connections and guarantee the necessary quality of service (QoS). This paper proposes a novel seamless and proactive end-to-end mobility management system, which can maintain the connections based on the end-to-end principle by incorporating an intelligent network status detection mechanism. The proposed system consists of two components, Connection Manager (CM) and Virtual Connectivity (VC). The CM, by using novel Media Access Control (MAC)-layer and physical-layer sensing techniques, can obtain accurate network condition while at the same time reducing the unnecessary handoff and ping-pong effect. The VC, can make mobility transparent to applications without additional network-layer infrastructure support using a Local Connection Translation (LCT), and can handle mobility well in Network Address Translator (NAT) and simultaneous movement cases using a Subscription/Notification (S/N) service. The proposed system enjoys several unique advantages: 1) capable of reacting to roaming events proactively and accurately; 2) maintaining the connection’s continuity with small handoff delay; and 3) being a unified end-to-end approach for both IPv4 and IPv6 networks. We have built a prototype system and performed experiments to demonstrate the advantages of the proposed system. Index Terms-WWAN/WLAN handoff, network condition detection, mobility management.

Future computer environments will include mobile computers which will either be disconnected, weakly inter-connected by low speed wireless networks such as GSM, or fully inter-connected by high speed networks ranging from Ethernet to ATM. Such environments place unique demands on systems, requiring software to dynamically adapt to rapid and significant fluctuations in communications quality-of-service (QoS). This paper reviews existing adaptation techniques and describes an experiment in developing an adaptive mobile application and associated distributed systems platform. The experiences gained during this experiment are presented and analysed to provide a basis for the engineering of future adaptive systems. 1. Introduction Future computer environments will include mobile computers which will either be disconnected, weakly inter-connected by low speed wireless networks such as GSM, or fully inter-connected by high speed networks ranging from Ethernet to ATM [Davies,96]. While the t...

Office delivery robots have to perform many tasks such as picking up and delivering mail or faxes, returning library books, and getting coffee. They have to determine the order in which to visit locations, plan paths to those locations, follow paths reliably, and avoid static and dynamic obstacles in the process. Reliability and efficiency are key issues in the design of such autonomous robot systems. They must deal reliably with noisy sensors and actuators and with incomplete knowledge of the environment. They must also act efficiently, in real time, to deal with dynamic situations. To achieve these objectives, we have developed a robot architecture that is composed of four layers: obstacle avoidance, navigation, path planning, and task planning. The layers are independent, communicating processes that are always active, processing sensory data and status information to update their decisions and actions. A version of our robot architecture has been in nearly daily use in our building...

In this paper, we present a network architecture for vehicle communication based on Mobile IP. The special network environment of a car allows optimizations but also requires modifications of existing approaches. We identify these issues and discuss the integration of possible solutions into the framework. For example, location information provided by a car navigation system can be used to improve handoff decisions and connectivity. To evaluate the architecture, simulation studies were carried out with the ns Network Simulator. This paper also gives an overview of the necessary modifications and extensions to ns and additional tools to simplify future research in this area.

A mobile ad-hoc network (MANET) is formed by a cluster of mobile hosts, each installed with a wireless transceiver, without the assistance of base stations. Due to the transmission range constraint of transceivers, two mobile hosts can communicate with each other either directly, if they are close enough, or indirectly, by having other mobile hosts relay their packets. Several routing protocols, such as DSR, SSA, AODV, and ZRP, have been proposed for a MANET with a dynamically changing topology. In a MANET, a route may suddenly become broken because only one host roams away. Even if a route remains connected, it may become worse due to host mobility or a better route newly being formed in the system. Existing protocols, however, will stick with a fixed route between a source-destination pair once it is discovered, until it is expired or broken. In this paper, we show how to enhance several existing protocols with route optimization and local route recovery capability, such that the rout...

Incorporating mobile components into a distributed system has posed new challenges to the design of distributed computation. This paper studies a fundamental problem in distributed computing, the termination detection problem, in a mobile environment. Two types of termination detection protocols already exist: the diffusionbased schemes [3, 10] and the weight-throwing schemes [6, 13, 18], that are designed for traditional static distributed systems. We propose a hybrid scheme by combining these two protocols together. The scheme can better exploit the communication hierarchy (in terms of wired and wireless bandwidths) and can pave the gaps of computation and communication capability between static and mobile hosts, thus more scalable to larger distributed systems. Simulation results are presented, which show the advantage of the hybrid scheme over existing schemes. 1 Introduction One major breakthrough in computer communication technologies recently is the extension of transmission m...