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SangKeun Lee, Chong-Sun Hwang and HeonChang Yu
Korea University

In a mobile computing environment, caching of frequently accessed data has been shown to be a useful technique for reducing contention on the narrow bandwidth of the wireless channels. However, the traditional client/server strategies for supporting transactional cache consistency that require extensive communications between a client and a server are not appropriate in a mobile computing environment. In this paper, we propose a new protocol, called OCC-UTS ( Optimisitic Concurrency Control with Update TimeStamp), to support transactional cache consistency in a wireless mobile computing environment by utilizing the broadcast-based solutions for the problem of invalidating caches. The consistency check on accessed data and the commitment protocol are implemented in a truly distributed fashion as an integral part of cache invalidation process, with most burden of consistency check being downloaded to mobile clients. Also, our experiments based on an analytical model substantiate the basic idea and study the performance characteristics. Experimental results show that OCC-UTS protocol without local cache outperforms other competitor protocol, and the more frequent a mobile client accesses data items the more efficient OCC-UTS protocol with local cache is. With respect to disconnection, a mobile client aborts its transaction if it disconnects more than the invalidation broadcast window size. Thus, the tolerance to disconnection is improved if the invalidation broadcast window size is extended. (See also talk given by SangKeun Lee)


Margaret H. Dunham
Southern Methodist University


Vijay Kumar
University of Missouri-Kansas City

We examine the impact of mobility on three different options to managing mobile transactions. Using an analytic performance study we show that no one management approach is always the best and that the performance is impacted by the location management strategy used. The primary objective of this work is to illustrate that the underlying implementation strategies do indeed impact mobile transaction processing and should be considered when proposing mobile transaction processing techniques. (Download related talk given by Margaret H. Dunham [postscript])


Cris Pedregal Martina
University of Massachusetts


Krithi Ramamritham
University of Massachusetts
and I.I.T. Bombay

Mobile applications increasingly require transaction-like properties, particularly those of recovery. Because there is a lack of abstractions to decompose the machinery of recovery, realizing recovery is difficult and error-prone, especially in a novel context like mobile systems.

We introduce recovery guarantees to tackle this problem by characterizing the assurances relevant to recovery that a subsystem must give to another. They describe the what can be expected but not the how it is implemented for recovery. Guarantees are complemented by recovery protocols, which prescribe behaviors subsystems should follow in order to take advantage of the guarantees.

In this paper we use the notions of recovery guarantees and protocols to show the relationships, vis-a-vis recovery, between the components of a mobile system. Our analysis shows which components of recovery remain unchanged (from a conventional recovery design) and which respond to the particular needs of mobile systems. This sheds light not just on how to do recovery on mobile systems but also on the nature of recovery in general. (See also talk given by Cris Pedregal Martina)


James Beck, Alain Gefflaut and Nayeem Islam
IBM T. J. Watson Research Center

MOCA is an adaptable service framework targeting mobile computing devices with limited memory footprint. To ensure portability across a large spectrum of these devices, it is written in Java. MOCA is based on the notion of services, and assumes that applications can be decomposed into sets of cooperating services. A service is a loadable software component that performs a specific function such as data encryption or caching. The MOCA framework is composed of a service registry and a set of essential services. The registry provides life-cycle management of services including dynamic registration and look-up. Essential services, stored on the device, provide the minimum functionality required to establish a generic secure computing environment on top of a Java Virtual Machine (JVM). In particular, MOCA securely supports multiple applications as well as optional services running on a single JVM. Optional services and applications can reside locally on the device or be dynamically downloaded from remote locations. MOCA also allows a device to adapt to its environment by enabling dynamic discovery and registration of remote services published by surrounding devices. A single mechanism is used to support both local and remote services, which allows a device to access remote services on other devices as if these services were local to the device itself. Unique features of MOCA include a distributed service discovery model, use of a single registry for both local and remote services, and a lazy service loading policy that minimizes memory consumption. (See also talk given by James Beck).


Barron Housel and Ian Shields
IBM Corporation

This paper describes the design of a system that significantly improves the performance of telnet data delivery for 3270 and 5250 emulation so that access to legacy applications via mobile units over low bandwidth wide area wireless networks is feasible. One of the key innovations of this technology is data stream caching. More generally, data stream caching can be used to reduce the transport volume for a broad class of data streams such as Lotus Notes or file transfer. The technology described herein is implemented in a system called Emulator Express (EE) [1], middleware that optimizes the operation of telnet 3270 and 5250 emulation. EE can be used with any wireless or wireline technology that implements the TCP/IP protocol. The success of the EE technology is reflected by some customers that report that the performance of running host applications when connected to their wireless networks often exceeds that of running the same applications when connected to a LAN. (Download related talk given by Barron Housel [pdf])


Patty Kostkova and Julie A. McCann
City University, London, UK

Computer systems no longer operate in centralized isolated static environments. Technological advances, such as smaller and faster hardware, and higher reliability of networks have resulted in the growth of mobility of computing and the need for run-time adaptability and reconfigurability.

However, mobile and roaming users need to dynamically adapt to local system configurations to order to fully utilize resources currently available, such as a fast network connection, an available colour printer etc. In order to provide support for this type of application, a dynamic resource manager supporting indirect resource requests and runtime reconfigurability is essential.

This paper proposes a new dynamic resource management architecture, MAGNET, to provide run-time adaptability for mobile applications. MAGNET enables the dynamic trading of resources which can be requested indirectly by the type of service they offer, rather than directly by their name. In addition, MAGNET enables runtime user-customized adaptation to services.


Andrew C. Huang, Benjamin C. Ling, Shankar Ponnekanti and Armando Fox
Stanford University

The first mass-produced pervasive computing devices are starting to appear -- the AutoPC, the Internet-connected ScreenFridge, and the combination Microwave Oven/Home Banking terminal. Although taken separately they appear bizarre, we believe they will play an important role in a world of pervasive computing. Specifically, these devices will accept or deliver information in the context in which it will be most useful, decoupling the information from the context in which it was originally created. We describe an extensible and modular architecture called Rome (to which all roads lead) that addresses this information-routing problem while leveraging significant existing work on composable Internet services and adaptation for heterogeneous devices. Rome's central abstraction is the concept of a trigger, a self-describing chunk of information bundled with the spatial and/or temporal constraints that define the context in which the information should be delivered. The Rome architecture manages triggers at a centralized infrastructure server and arranges for the triggers to be distributed to pervasive computing devices that can detect when the trigger conditions have been satisfied and alert the user accordingly. The main contribution of the architecture is an infrastructure-centric approach to the trigger management problem. We argue that pervasive computing devices benefit from extensive support in the form of infrastructure computing services in at least two ways. First, infrastructure adaptation services can help manage communication among heterogeneous devices. Second, access to public infrastructure services such as MapQuest and Yahoo can augment the functionality of trigger management because they naturally support the time- and location-dependent tasks typical of pervasive-computing users. We describe our experience with a functional prototype implementation that exploits GPS to simulate an AutoPC, and propose a research agenda to further the creation and deployment of pervasive-computing infrastructure based on the architecture we describe. (See also talk given by Andrew C. Huang)


Gaetano Borriello
University of Washington

As computing and communication technology advances and matures, we will transition into a consumer-driven mass-market. This market will consist of a wide range of interconnected task-specific devices and, unlike most of the past history of computing, the motivation will come from function and convenience rather than technological prowess. Our challenge is to build applications:

  • where the user interface is not on a computer, but is the computer;
  • where users do not connect to a network, but have their data travel on the network; and
  • where users are not explicitly issuing commands to be performed, but agents are operating autonomously on their intentions.

Although not as limited by computational speed or communication bandwidth as their predecessors, future devices will instead be constrained by limits on size, form-factor, and power consumption.

The problems in this new landscape are not simply the problems of mobile networking and palm-sized PDAs. For computing to reach the broadest spectrum of our population, the entire infrastructure and the devices themselves must be as invisible as possible, requiring little or no configuration and performing reliably and predictably. To accomplish this requires a review of our basic assumptions regarding user interfaces and network transactions. It challenges us to develop entirely new models for distributed services. User interfaces will have to be based on multiple types of input ranging from the user's physical movement, location, data available from the network, and a variety of sensor data we can only begin to imagine today. Network topologies will be intermittent and services will have to be discovered independently of user guidance. The network fabric will have to provide computing and storage cycles to the data bundles. Data will need to find its own way from the user to the services and back, possibly replicating itself along the way to prevent data loss. We will require an open services architecture that not only permits users to have their data directed to the appropriate services but also allows the services to interconnect with each other.

To make this vision a reality, crucial research must be carried out in at least three fundamental areas: user interfaces, network infrastructure, and distributed services. This presentation will outline the plans of the Portolano Project at UW, a DARPA Expedition, and the steps we will be taking to create a prototype of the future consumer computing landscape. (See also talk given by Gaetano Borriello).


Qun Ren and Margaret H. Dunham
Southern Methodist University

Semantic caching is particularly attractive for use in a mobile computing environment due to its content-based reasoning ability and the fact that only the required data (as opposed to a file or pages of data) is transmitted over the wireless link. In this paper we propose a cluster based approach to manage a semantic cache, aiming at examining and further making use of the semantic locality among queries in a workload. Cache replacement performance using this technique is shown to outperform that of an LRU scheme where only temporal locality is considered. (Download related talk given by Qun Ren [postscript])


Shirish Phatak  and  B. R. Badrinath
Rutgers University

The use of mobile computers is gaining popularity. The number of users with laptops and notebooks is increasing and this trend is likely to continue in the future where the number of mobile clients will far exceed the number of traditional fixed clients or desktops. Applications running on mobile clients download information by periodically connecting to repositories of data. Mobile clients constitute a new and different kind of workload and exhibit different access patterns than those seen in traditional client server systems.

In this paper, we argue with particular emphasis on databases, that the workload presented by mobile clients allows partitioning of a dataset on a server. The partitions are defined by constraints on specific attributes of the data called the hoard attributes. The techniques are general enough to be applied to other non-database applications that access collections of data, including filesystems such as CODA and FICUS. Our primary contribution is a set of simulation results that illustrate the performance of a sample database system with both disconnected and traditional clients. Furthermore, we argue that such partitioning of the server data set simplifies management of other issues, such as consistency management. (See also talk given by Shirish Phatak)


I. Stanoi, D. Agrawal, A. El Abbadi
University of California,
Santa Barbara


S. Phatak, B. R. Badrinath
Rutgers University

With rapid advancement in technology, mobile devices are increasingly becoming the norm. These devices are characterized by their need to operate even when they are disconnected from the fixed non-mobile world.  Since existing software technology is tuned to applications that operate in a fully connected world, this requirement of disconnected operation creates a need to adapt existing software technology to a partially disconnected world.

Databases and filesystems have already been adapted to operate in a partially disconnected environment. However, little work has been done in the context of data warehousing in such an environment. We believe that there is a real need for adapting existing data warehousing technology for the mobile world.  In this position paper, we show how techniques for hierarchical data warehouse management can be applied to data warehouses in a mobile environment.  The techniques can be extended for other mobile applications. We present a variety of alternatives for systems in which some of the sources of data as well as the data warehouse itself is mobile.


Eddie C. Shek, Son K. Dao, Yongguang Zhang, and Darrel Van Buer
HRL Laboratories

We have developed Intelligent Information Dissemination Services (IIDS) to support the dissemination and maintenance of extended situation awareness over a hybrid satellite-wireless network information infrastructure. One of the goals of IIDS is to transparently handle the mismatches in characteristics of satellite and terrestrial wireless networks, allow effective utilization of available bandwidth, and support timely delivery of highly relevant information. IIDS achieve the above by implementing user profile aggregation that incrementally aggregates users into communities sharing common interests to enable multicast-based information dissemination. Based on the user grouping, semantic profile matching customizes information streams based on matching user group interest profiles. By taking into account of expected changes in user profiles, profile-oriented data dissemination achieves predictive push and caching that anticipates future user needs and minimizes latency of data request by making data available before they are explicitly requested. The IIDS software has been deployed on the Digital Wireless Battlefield Network that integrates commercial off-the- shelf satellite and wireless products.


Tomasz Imielinski and Samir Goel
Rutgers University

In this paper, we present an architecture for the nextgeneration of systems --- systems based on fully distributedparadigm, and composed out of a collection of objects with twocommon characteristics: objects carrying data and having connectivity. We call such systems, DataSpace Systems. In ourarchitecture, we focus on supporting global directory service andglobal resource discovery efficiently in such an environment. Ourground principle is to treat network as a database machine.


Shu Jiang and Nitin H. Vaidya
Texas A&M University

Broadcasting is an effective way of delivering data to a large population. In the broadcast environment under consideration, a server broadcasts data items to all clients simultaneously, according to a certain transmission schedule. Users with pending data requests need to listen to the broadcast channel until their requests are satisfied by the transmitted data. Past research on broadcast scheduling assumes that once a user starts to wait for some data item, the user waits until the desired data item is transmitted by the server. This is often not true in practice. For various reasons, users may lose patience after waiting "too long'' and leave with their requests unserved.

In this paper, we study the broadcast scheduling problem taking user impatience into account. Based on our analytical results, we propose a scheduling algorithm that can produce a broadcast schedule with high service ratio (i.e., percentage of requests served) as well as low mean waiting time for the requests. Performance evaluation results based on simulations are provided. (Download related talk given by Nitin H. Vaidya [postscript])



Please send corrections, updates or suggestions regarding these pages to George Kyrou
Last modified on October 11, 1999