Elsevier

Computer Networks

Volume 35, Issue 4, March 2001, Pages 443-456
Computer Networks

A Web-based nomadic computing system

https://doi.org/10.1016/S1389-1286(00)00181-XGet rights and content

Abstract

CoolTown offers a Web model for supporting nomadic users, based on the convergence of Web technology, wireless networks and portable devices. This paper describes how CoolTown ties Web resources to physical objects and places, and how users interact with resources using the information appliances they carry, from laptops to smart watches. Enabling the automatic discovery of URLs from our physical surroundings, and using localized Web servers for directories, we create location-aware but ubiquitous systems. On top of this infrastructure we leverage device connectivity to support communication services.

Introduction

This paper describes work belonging to a research project at Hewlett-Packard Laboratories called CoolTown [7]. CoolTown combines Web technology, portable devices, and wireless communications to explore new kinds of systems, systems similar to nomadic [21] or ubiquitous [31] computing systems. Here we will show how a system created from elements of the CoolTown project form a basis for nomadic computing.

CoolTown operates from the premise that the Web and the technologies behind the Web provide a sound basis for pervasive nomadic computing. This premise is based on the Web's potential to realize ubiquitous access, its lightweight software requirements, and its ability to operate locally as well as on a global scale. We start with a discussion of these properties.

Ubiquitous access. The Web supports pervasive computing because it is accessible in a large and rapidly growing number of places. This growth is a consequence of its design. The Web relies on a simple standard, the HTTP protocol [17], which can be implemented on a vast variety of devices. This includes devices that the user carries: general-purpose devices such as personal digital assistants (PDAs) and laptops, and information “appliances” dedicated to a specific function, such as digital cameras and printers [11]. Furthermore, the Web supports mobile users through its flexible global addressing scheme, allowing them transparent access to resources outside their current environment. Finally, the Web addressing and communications model can be bridged into devices that do not support TCP/IP.

Just enough middleware. The diversity of the devices that mobile users may carry and encounter argues against specific software based on device type or even application type. It also argues against assuming that all devices will run a form of middleware, such as Java or CORBA, that is heavy on the commitments it imposes at the application, language, or resource level. Rather we believe that the Web standards of HTTP and URLs [4] have proven themselves to support adaptation to diversity. The form of interaction with particular devices and other entities should be encoded using XML [12] documents and MIME types, not binary formats and language-specific interface signatures. Our demonstrations include a variety of digital devices that we can integrate with minimal additional software.

Locality. We will demonstrate how to deliver Web resources to nomadic users as they encounter new environments, without requiring a global wireless connection like a cell-phone, and without necessarily requiring any networking access beyond the immediate surroundings. This has the advantage of minimizing how much of the infrastructure needs to be up and running in order for users to interact with local services. For example, a mobile user should be able to print a document at a nearby printer without necessarily having to contact any global services. A local Web server should be enough, and sometimes even a simple peer-to-peer interaction will suffice. Moreover, the user can discover and access these local resources without having to reconfigure their devices as they move from place to place.

While we believe these properties to be necessary for a pervasive computing solution, they are not sufficient to support nomadic users. Among the problems are:

  • •

    The Web grew out of the need for electronic document exchange, whereas nomadic users require information and interaction based around the physical entities in their environment.

  • •

    The Web relies on verbal or text-exchange of addresses for “resource discovery”. For example, one Web user will tell another “look at cooltown.hp.com”. Nomadic users will need new resource addresses continually and may not have easy access to keyboards: the Web model for resource discovery is not adequate.

  • •

    URLs are too bulky and volatile for routine use as identifiers.

  • •

    The Web is largely a read-only system supporting “browsers”; most content is placed on the Web through non-Web avenues that therefore do not have its pervasive properties.

The CoolTown project seeks to expand the Web model to support pervasive non-desktop computing and nomadic users in particular. We call the representation of physical entities on the Web “Web presence”; [20] describes our initial efforts to build and maintain Web presence. We discuss the other three issues in this paper.

Section snippets

Nomadic computing model

CoolTown builds on HP Labs' experience in the development of embedded Web servers [11] and systems of communicating appliances [19]. Our approach to nomadic users extends work on mobile Web browsers (“wireless Web”) to support the augmentation of physical entities in the environment with Web resources. In this way we see our work as combining the physical information systems work of Xerox PARC [27], [29] with the Web.

Our work describes an approach to system development based on assumptions

Sensing

In this section, we describe the bottom layer of our infrastructure, which enables the user to acquire URLs from their surroundings or from the physical entities in their surroundings. An obvious mechanism, with equally obvious drawbacks, is to write the URL on a label and attach it to the object. The user reads the label and types the URL into their browser.

Rather than being forced to use that cumbersome method, users should be able to identify conveniently what it is that interests them in

Context and physical discovery

By attaching beacons or tags to easy-to-find points on physical entities or in physical places and by storing appropriate URL values in them (or in the resolver for them), we can create a connection between the entity or place and a Web page. When a user approaches a beacon or tag they can use their device to find the corresponding Web page. The user has “discovered” an electronic representation. This physical discovery involves the user in physically designating which places and things are of

Content exchange

Up to this point we have described how a nomadic user can enter a new place, obtain the address of the place context, and then browse the resources there. The level of function provided by (read-only) browsing is adequate for some nomadic tasks, but other tasks require more interactions with resources. In this section we discuss content exchange, a simple approach to interaction.

Content exchange supports the opposite of browsing: the nomadic user can push content into the pervasive

Place contexts

In general, place contexts can be defined not only in terms of the physical domain but also in terms of other factors, such as the time of day, the identity of the user, the user's device, and the user's current activity. Some of these factors have been explored in tourist guides [9] and other applications such as overviews of working groups and meetings [26].

Section 4, for the sake of simplicity, shows only how places are defined irrespective of factors such as time of day. In fact, the data

Conclusion

We have outlined many of the important issues any system supporting nomadic users of pervasive systems must face, and provided Web-based solutions to many of them. Critical to our approach is technology to connect physical objects and places with their corresponding Web presence. We have a good deal of progress in that area. The Web presence for places and its use as a context for nomadic users has been explored. Mechanisms for nomadic users to exchange content with each other and with devices

Acknowledgments

The work described here contains contributions from many people in the Cooltown project. The concept and demonstration of the URL beacons is due to Jeff Morgan, Marcos Frid, Bill Serra, and John Schettino. The content transfer ideas came from the HP JetSend team with special thanks to Peter Willams and from Jeff Morgan. We also thank Gene Becker and Gita Gopal for helpful discussions.

Tim Kindberg's research interests include distributed systems, pervasive computing and computer supported collaborative working (CSCW). He currently works for HP Laboratories, Palo Alto, as a member of the CoolTown project. There he is investigating modes of correlation between physical and virtual entities, and security in pervasive computing environments. He was previously a senior lecturer in the Computer Science department at Queen Mary College, University of London, where he led and

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    Tim Kindberg's research interests include distributed systems, pervasive computing and computer supported collaborative working (CSCW). He currently works for HP Laboratories, Palo Alto, as a member of the CoolTown project. There he is investigating modes of correlation between physical and virtual entities, and security in pervasive computing environments. He was previously a senior lecturer in the Computer Science department at Queen Mary College, University of London, where he led and participated in projects on CSCW and middleware for distributed multimedia. He holds a Ph.D. in Computer Science from the University of Westminster and a B.A. in Mathematics from the University of Cambridge. He is co-author of the textbook “Distributed Systems – Concepts and Design”. Email: [email protected].

    J. Barton works on software infrastructure to support coordinated data input from digital appliances like cameras and PDAs. This work is part of the HP Labs Cooltown project. Before joining HP in 1998, he worked IBM's T.J. Watson Research Center. There he wrote the Jalapeno Java Virtual Machine boot image writer and managed the Java Technology group. Before that he worked on the “Montana” research project that led to IBM's VisualAge C++ v 4.0 product and co-authored “Scientific and Engineering C++” with Lee R. Nackman. He has a Ph.D. degree in Chemistry from the University of California at Berkeley and a Master's degree in Applied Physics from the California Institute of Technology. Email: [email protected].

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