R. Bagrodia, M. Gerla, L. Kleinrock, J. Short, T.-C. Tsai, A Hierarchical Simulation Environment for Mobile Wireless Networks
A hierarchical simulator has been designed for multimedia communication protocols in a wireless mobile environment. The hierarchical approach integrates performance evaluation of protocols with their implementation. This approach supports availability studies of the protocols in an efficient manner using coarse-grain models that abstract implementation details of the protocol and is execution environment by a few key parameters. Fine-grain, low-level models that capture implementaiton details are used for detailed evaluation of small networks and for automatic implementation on radio platforms. The design, evaluation, and implementation cycle is closed by feeding the measurements from the implementation back into the model to improve its accuracy. The paper describes the use of the environment in the evaluation and implementation of a cluster-based, multihop protocol for multimedia traffic.
R. Guy, T. Page, J. Heidemann, and G. Popek, Name Transparency in Very Large-Scale Distributed Systems
Previous distributed file systems have relied on either convention or obtaining dynamic global agreement to provide network transparent file naming. This paper argues that neither approach can succeed as systems scale to the kind of size that is anticipated in the current decade. We propose instead a novel name-mapping scheme which relies on a fragmented, selectively replicated name translation database. Updates to the naming database are coordinated by an optimistic concurrency control strategy with automatic propagation and reconciliation. A prototype of this name-mapping mechanism has been implemented and is in use in the Ficus replicated file system.
L. Kleinrock, Nomadic Computing - An Opportunity
We are in the midst of some truly revolutionary changes in the field of computer communications, and these offer opportunities and challenges to the research community. One of these changes has to do with nomadic computing and communications. Nomadicity refers to the system support needed to provide a rich set of capabilities and services to the nomad as he moves from place to place in a transparent and convenient form. This new paradigm is already manifesting itself as users travel to many different locations with laptops, PDAs, cellular telephones, pagers, etc. In this paper we discuss some of the open issues that must be addressed as we bring about the system support necessary for nomadicity. In addition, we present some of the considerations with which one must be concerned in the area of wireless communications, which forms one (and only one) component of nomadicity.
G. Kuenning, The Design of the SEER Predictive Caching System
Supporting portable computers in a disconnected environment will require persistent caching of files without user intervention. SEER is a system that uses semantic information to predict on which files the user is likely to work, and arranges to transparently cache them on the portable platform prior to disconnection. We present the overall design of the SEER system and the algorithms used to determine semantic relationships.
G. Kuenning, G. Popek, P. Reiher, An Analysis of Trace Data for Predictive File Caching in Mobile Computing
One way to provide mobile computers with access to the resources of a network, even in the absence of communication, is to predict which information will be used during disconnection and cache the appropriate data while still connected. To determine the feasibility of this approach, traces of file-access activity for three diverse application domains were collected for periods of over two months. Analysis of these traces using traditional and new measures reveals that user working sets tend to be small compared to modern disk sizes, that users tend to reference the same file for several days or even weeks at a time, and that different users do not tend to write to the same file except in highly constrained circumstances. These factors encourage the conclusion that an automated caching system can be built for a wide variety of environments.
J. Short, R. Bagrodia, L. Kleinrock, Mobile Wireless Network System Simulation
In this paper a simulation environment is described which is used to examine, validate and predict the performance of mobile wireless network systems. This simulation environment overcomes many of the limitations found with analytical models, experimentation, and other commercial network simulators available on the market today. This paper describes the simulation language, Maisie, which is used to analyze the performance bottlenecks of a multimedia wireless network system being developed at UCLA. By modeling the various components and their integration, this simulation environment is able to accurately predict the performance bottlenecks of the UCLA wireless multimedia networking terminal, determine the trade-off point between the various bottlenecks, and provide performance measurements which are not possible through experimentation and too complex for analysis.
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