Final Report1

INTRODUCTION Mobile computing means different things to different people. Ubiquitous, wireless and remote computing. Wireless and mobile computing are not synonymous. Wireless is a transmission or information transport method that enables mobile computing. MOBILE COMPUTING FRAMEWORK: Mobile computing is expanding in four dimensions (a)Wireless delivery technology and switching methods: • Radio- based systems • Cellular communications • Wireless packet data networks • Satellite networks Infrared or light based mobile computing (b)Mobile information access device: • Portable Computers • PDA • Palmtops (c) Mobile data internetworking standards and equipments: • CDMA • IrDA (d) Mobile computing based business application: Dreams behind mobile computing: 1

Location based services: •

Elements of location based services:  Geocoding: This is a task of processing textual address to add a positional co-ordinate to each address. These co-ordinate are then indexed to enable the address to be searched geographically in ways such as “find me my nearest”. •

Latitude: the first component of a spherical cell based system used to record positions on the earth‘s surface. Latitude which gives the location of a place north or south of the equator is expressed by angular measurement ranging from 0 at the equator to 90 at the pole.

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Longitude: latitude, the location of a place east or west of a north south line called the prime meridian, is measured in angles ranging from 0 at the prime meridian to 180 at the International Date Line. The international date line passes through London’s Greenwich observatory, UK.

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Map content :

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Proximity searching: this is very important element of LBS.

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Routing and driving directions: it is a interaction between the users location and a planned destination. Routes can be calculated and displayed on the map and driving directions can be provided according to shortest distance or the fastest route. 2

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Rendering: this is a production of maps for display onto the screen of the device. Rendering images are typically personalized according to the specific LBS request.

GPS in LBS world The global positioning system is a network is a network of 24 Navstar satellites orbiting earth at 11000 miles. Dod has established it at the cost of about US $ 13 billion, access to GPS to all users including those in other countries. GPS provides specially coded satellite signals that can be processed by GPS receiver. Basically GPS works by using four GPS satellite signals to compute positions in three dimensions In the receiver clock. Operation control system has the responsibility for maintaining the satellite and its proper positions. How GPS finds where you are: Complex error correction used by satellite to determine the accurate speeds. Here are some techniques to make improvements in LBS system. •

Time of arrival: here the differences in the time of arrival of the signal from the mobile to more than one base station are used to calculate the location of the device.

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Angle of arrival: AOA is a system that calculates the angle at which a signal arrives at two base stations from the handset, using triangulation to find location.

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UBIQUITOUS COMPUTING Firstly introduction of pervasive computing is necessary Pervasive computing this implies that computer has the capability to obtain information from the environment in what it is embedded and utilized to dynamically build model of computing. Input interface of pervasive computing utilizes “Multimodal “interface and that means developing systems that can recognize voice and gestures. WHAT IS UBIQUITOUS TECHNOLOGY? Ubiquitous computing is intangible-physically, figuratively, literally, living and working environments embedded with computing devices in a seamless, invisible way. True ubiquitous computing involves devices embedded transparently in our physical and social movements, integrating both mobile and pervasive computing. Ubiquitous computing represents a situation in which computers will be embedded in our natural movements and interactions with our environments both physical and social. UC will help to organize and mediate social interactions wherever and whenever these situations might occur. UC TECHNOLOGIES UC represents amalgamation of quite a number of existing and future technologies like “mobile computing, pervasive computing, wearable computing,

embedded

computing

location,

context-aware

computing

technologies” fulfill the dreams of bringing UC into reality. Software Infrastructure and Design Challenges for UC Applications

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Ubiquitous computing applications will be embedded in the user’s physical environments and integrate seamlessly with their everyday tasks. •

Task dynamism- UC applications, by virtue by virtue of being available everywhere at all times, will have to adapt to the dynamism of user’s

environment

and

the

resulting

uncertainties

.in

these

environments; user may serendipitously change their goals or adapt their actions to a changing environment. •

Device Heterogeneity and Resource Constraints – the omnipresence of UC applications is typically achieved by either making the technological artifacts (devices) move with the user or having the applications move between devices tracking the user. In both cases, applications have to adapt to changing technological capabilities in their environment.

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Computing in a Social environment – another major characteristic of UC technology is that it has a significant impact on the social environments in which it is used. An introduction of a UC environment implies the introduction of sensors, which irrevocably have an impact on social structure.

Research Challenges: •

Semantic modeling – A fundamental necessity for an adaptable and compos able computing environment is the ability to describe the preferences of users and the relevant characteristics of computing components using a high level semantic model.

Ontology can be used to describe user’s task environment, as well as their goals, toanable reasoning about a user’s needs and therefore dynamically adapt to changes .the research challenges in semantic modeling include 5

developing a modeling language to express the rich and complex nature of ontology’s, developing and validating for various domains of user activity. •

Building the Software Infrastructure – An effective software infrastructure for running UC applications must be capable of finding, adapting and delivering the appropriate applications to the user’s context.

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Developing and Configuring Applications – Currently services are being described using a standard description language and in the future, using standard ontologies such semantic descriptions could enable automatic composition of services, which in turn enables an infrastructure that dynamically adapts to tasks.

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Validating the user experience – the development of effective methods for testing and evaluating the usage scenarios enabled by pervasive applications is an important area that needs more attention from researchers.

Design of user interfaces for UC The mobile access is the gateway technology required to make information available at any place and at any time. In addition the computing system should be aware of user’s context not only to be able to respond in an appropriate manner with respect to the user’s cognitive and social state but also to anticipate needs of the users. Speech recognition, position sensing and eye tracking should be common inputs and in the future, stereographic audio and visual output will be coupled with 3D virtual reality information. In addition heads-up projection displays should allow superposition of information onto the user’s environment. 6

UC technologies benefits The most profound technologies are those that disappear and weave themselves into the fabric of everyday life until they are indistinguishable from it. It will have profound effect on the way people access and use services that only make sense by virtue of being embedded in the environment. Trends of Computing:

Graph: Mobility & Embeddebness

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Scenario of virtual reality &Ubiquitous Computing

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Network Structure

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]Infrared Data Association LAN Access Extensions for Link Management Protocol (IrLAN) Introduction The creation of the IrDA protocols and their broad industry support has led to IrDA-compliant infrared ports becoming common on laptop computers. With the IrDA approval of the higher media speeds of 1.15 and 4 megabits per second (Mbps), the infrared link is becoming fast enough to support a network interface. This document describes a protocol, conforming to the IrDA specifications, that has these features:  E nables a computer with an IrDA adapter to attach to a local area network (LAN) through an access point device that acts as the network adapter for the computer. Enables two computers with IrDA adapters to communicate as though they were attached through a LAN. Enables a computer with an IrDA-compliant adapter to be attached to a LAN through a second computer that is already attached to the LAN (the second computer must also have an IrDA-compliant adapter). The proposed protocol, the infrared LAN (IrLAN) protocol, should allow for interoperability of all devices supporting the protocol. Design Goals The IrLAN protocol has these design goals: The IrLAN protocol deals with the issues associated with running legacy networking protocols over an infrared link. It supports three different operating modes that represent the possible configurations between infrared devices and between infrared devices and an attached network. 10

From a client operating-system perspective, the IrLAN protocol must be implemented completely as a set of network media-level drivers. No modification of the existing network protocols should be necessary. The IrLAN protocol must not impose excessive processing constraints on access point devices, which may be implemented with slower processors than typically found in modern computers. Definition of Terms The following technical terms are used in this document. Control channel An IrLMP communication channel used by the client and offered by the provider to allow for the setup and configuration of a data channel. Data channel An IrLMP communication channel used by the client and provider to exchange LAN-formatted packets. Frame (or media frame) A block of data on the media. A packet may consist of multiple media frames.

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IAS (information access service) Part of the IrDA protocol suite, the IAS is a standard IrLMP client that implements a local store of configuration information. Information is stored under a primary key called the class and under sub keys in each class called attributes. The class may only contain sub keys, each of which is unique in the class, and each sub key may contain a corresponding value, which may be a string or an integer. Multiple objects of the same class are allowed, and each object in the IAS may be read by a remote station supporting the IAS protocol. IrLAN client (or client) The station in an IrLAN link that is using the IrLAN services of a provider to set up an IrLAN link. The client is the active component in the IrLAN protocol; it issues requests to the IrLAN provider to establish a data link and to configure the link. IrLAP (Infrared Link Access Protocol) A protocol, based on the HDLC protocol, designed to control an infrared link. IrLAP provides for discovery of devices, their connection over an infrared link, and reliable data delivery between devices. IrLMP (Infrared Link Management Protocol) A multiplexing protocol designed to run on top of IrLAP. IrLMP is multipoint-capable even though IrLAP is not. When IrLAP becomes multipoint-capable, multiple machines will be able to communicate concurrently over an infrared link. Infrared LAN access point device A network adapter with an infrared link to the LAN client. Conceptually, the infrared link is the bus that the LAN card resides on. 12

LAN A local area network. LSAP (logical service access point) A unique 1-byte identifier used by IrLMP to multiplex and demultiplex packets sent using IrLAP. Clients of IrLMP logically open an LSAP and then attach it to a remote node, or receive attachment from a remote node. Clients typically advertise their LSAP to other clients by writing entries in the local IAS. NIC (network interface controller) A piece of hardware designed to transmit and receive packets on a LAN network. Packet A block of data that is transmitted or received over the media. The media may break a packet down into several media frames to deliver it. Primary station A term used in IrLAP to specify the station that is controlling the infrared link. The other side of the link is where the secondary station resides (or secondary stations reside). No secondary station can transmit without receiving permission from the primary station. IrLAN Provider (provider) The station in an IrLAN link that is providing the IrLAN protocol interface.

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Secondary station A term used in IrLAP to specify a station that is controlled by the primary station. The secondary station can send when it receives permission from the primary station. TinyTP A lightweight protocol, supporting flow control and segmentation and reassembly, that is designed for use over an IrLMP connection. Window size One of the parameters negotiated between the two infrared nodes as part of establishing an IrLAP connection. The window size specifies the number of consecutive IrLAP frames that a node can transmit before it must allow the other node an opportunity to transmit. The maximum IrLAP window size is seven frames. Overview The IrLAN protocol is a “sided” protocol that defines a two-channel interface between a protocol client and a protocol server. An IrLAN provider is passive. It is up to the IrLAN client to discover and then attach to the provider and open up a data channel over which LAN packets can be transmitted and received. In IrLAN peer-to-peer mode (which is also described in “Access Methods”), each station has both an IrLan client and provider. There is a race to determine which node will open the Data channel. This race condition is resolved by the protocol in State Machines described later in this document. The client begins setting up the connection by reading an object’s information in the provider’s IAS. The object specifies an IrLMP LSAP for the “control channel.” The client connects to the control channel and uses the control channel to negotiate the characteristics of a data channel. Once the data 14

channel has been negotiated, it is opened and then configured. All configurations are handled through the control channel. The data channel is used solely for the transmission and reception of packets formatted for the LAN. The IrLAN protocol defines a graceful close, but it is seldom used because it would require user intervention to initiate a disconnect. Typically, the connection will close down “ungracefully” through an IrLAP connection timeout. Both the control and data channels use the TinyTP protocol for segmentation and reassembly of packetsand for flow control. Access Methods The IrLAN protocol is intended to support these modes of operation:  Access point  Peer-to-peer  Hosted Access Point Mode An access point device is hardware supporting both a LAN network interface controller (NIC) and an infrared transceiver. For communication over the infrared link, the access point device runs a protocol stack that conforms to the IrDA standards and runs the IrLAN protocol over the IrDA stack. The access point device implements a network adapter for the client using infrared as the bus for accessing the adapter. The following illustration shows the access point mode of operation.

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Filtering information is passed from the client to the access point device to minimize the transmission of unwanted traffic over the infrared link. In this case, the access point device assigns a unique UNICAST address to each client connecting to the device. It is quite reasonable to expect future implementation of access point devices to support multiple concurrent clients connecting to the LAN. In this case, each client would be assigned a unique LAN address, and the access point device would likely use a NIC supporting multiple concurrent UNICAST addresses. Peer-to-Peer Mode The IrLAN protocol peer-to-peer mode allows nodes running network operating systems that are peer-to-peer capable to create ad-hoc networks. The following illustration shows the peer-to-peer mode. 16

In peer-to-peer mode, there is no physical connection to a wired LAN. Filtering information can still be sent to the provider during the connection setup process. The filters allow the provider to lower traffic when both peers are not running the exact same protocol suites. Also, the filters can lower traffic in the case of Point-to-multipoint traffic. In peer-to-peer mode, each peer must provide a Server Control LSAP in addition to its Client Control LSAP and Data LSAP. Each Client Control LSAP connects to its peer’s Server Control LSAP. This allows each node to establish and control its peer’s Data LSAP using the command set described herein.

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Hosted Mode In hosted mode, the provider has a wired network connection, but has multiple nodes attempting to communicate through the wired connection. The following illustration shows hosted mode.

Unlike access point mode, both the host machine and the client(s) share the same NIC address in host mode. To make host mode work, the host must run special bridging and routing software that will handle the proper routing of packets. The algorithms used in this mode are highly protocol-dependent. Some Computer Science Issues in Ubiquitous computing Ubiquitous computing is the method of enhancing computer use by making many computers available throughout the physical environment, but making them effectively invisible to the user. Since we started this work at 18

Xerox PARC in 1988, a number of researchers around the world have begun to work in the ubiquitous computing framework. This paper explains what is new and different about the computer science in ubiquitous computing. It starts with a brief overview of ubiquitous computing, and then elaborates through a series of examples drawn from various sub disciplines of computer science: hardware components (e.g. chips), network protocols, interaction substrates (e.g. software for screens and pens), applications, privacy, and computational methods. Ubiquitous computing offers a framework for new and exciting research across the spectrum of computer science. A few places in the world have begun work on a possible next generation computing environment in which each person is continually interacting with hundreds of nearby wirelessly interconnected computers. The point is to achieve the most effective kind of technology, that which is essentially invisible to the user. To bring computers to this point while retaining their power will require radically new kinds of computers of all sizes and shapes to be available to each person. I call this future world "Ubiquitous Computing" (short form: "Ubicomp") [Weiser 1991]. The research method for ubiquitous computing is standard experimental computer science: the construction of working prototypes of the necessary infrastructure in sufficient quantity to debug the viability of the systems in everyday use, using ourselves and a few colleagues as guinea pigs. This is an important step towards insuring that our infrastructure research is robust and scalable in the face of the details of the real world. The idea of ubiquitous computing first arose from contemplating the place of today's computer in actual activities of everyday life. In particular, anthropological studies of work life [Suchman 1985, Lave 1991] teach us that people primarily work in a world of shared situations and unexamined technological skills. However the computer today is isolated and isolating from the overall situation, and fails to get out of the way of the work. In other words, 19

rather than being a tool through which we work, and so which disappears from our awareness, the computer too often remains the focus of attention. And this is true throughout the domain of personal computing as currently implemented and discussed for the future, whether one thinks of PC's, palmtops, or dynabooks. The characterization of the future computer as the "intimate computer" [Kay 1991], or "rather like a human assistant" [Tesler 1991] makes this attention to the machine itself particularly apparent. Getting the computer out of the way is not easy. This is not a graphical user interface (GUI) problem, but is a property of the whole context of usage of the machine and the affordances of its physical properties: the keyboard, the weight and desktop position of screens, and so on. The problem is not one of "interface". For the same reason of context, this was not a multimedia problem, resulting from any particular deficiency in the ability to display certains kinds of realtime data or integrate them into applications. (Indeed, multimedia tries to grab attention, the opposite of the ubiquitous computing ideal of invisibility). The challenge is to create a new kind of relationship of people to computers, one in which the computer would have to take the lead in becoming vastly better at getting out of the way so people could just go about their lives. In 1988, when I started PARC's work on ubiquitous computing, virtual reality (VR) came the closest to enacting the principles we believed important. In its ultimate environment, VR causes the computer to become effectively invisible by taking over the human sensory and effects systems [Rheingold 91]. VR is extremely useful in scientific visualization and entertainment, and will be very significant for those niches. But as a tool for productively changing everyone's relationship to computation, it has two crucial flaws: first, at the present time (1992), and probably for decades, it cannot produce a simulation of significant verisimilitude at reasonable cost (today, at any cost). This means that users will not be fooled and the computer will not be out of the way. Second, and most importantly, it has the goal of fooling the user -- of leaving 20

the everyday physical world behind. This is at odds with the goal of better integrating the computer into human activities, since humans are of and in the everyday world. Ubiquitous computing is exploring quite different ground from Personal Digital Assistants, or the idea that computers should be autonomous agents that take on our goals. The difference can be characterized as follows. Suppose you want to lift a heavy object. You can call in your strong assistant to lift it for you, or you can be yourself made effortlessly, unconsciously, stronger and just lift it. There are times when both are good. Much of the past and current effort for better computers has been aimed at the former; ubiquitous computing aims at the latter. The approach I took was to attempt the definition and construction of new computing artifacts for use in everyday life. I took my inspiration from the everyday objects found in offices and homes, in particular those objects whose purpose is to capture or convey information. The most ubiquitous current informational technology embodied in artifacts is the use of written symbols, primarily words, but including also pictographs, clocks, and other sorts of symbolic communication. Rather than attempting to reproduce these objects inside the virtual computer world, leading to another "desktop model" [Buxton 90], instead I wanted to put the new kind of computer also out in this world of concrete information conveyers. And because these written artifacts occur in many different sizes and shapes, with many different affordances, so I wanted the computer embodiments to be of many sizes and shapes, including tiny inexpensive ones that could bring computing to everyone. The physical affordances in the world come in all sizes and shapes; for practical reasons our ubiquitous computing work begins with just three different sizes of devices: enough to give some scope, not enough to deter progress. The first size is the wall-sized interactive surface, analogous to the 21

office whiteboard or the home magnet-covered refrigerator or bulletin board. The second size is the notepad, envisioned not as a personal computer but as analogous to scrap paper to be grabbed and used easily, with many in use by a person at once. The cluttered office desk or messy front hall table are real-life examples. Finally, the third size is the tiny computer, analogous to tiny individual notes or PostIts, and also like the tiny little displays of words found on book spines, light switches, and hallways. Again, I saw this not as a personal computer, but as a pervasive part of everyday life, with many active at all times. I called these three sizes of computers, respectively, boards, pads, and tabs, and adopted the slogan that, for each person in an office, there should be hundreds of tabs, tens of pads, and one or two boards. Specifications for some prototypes of these three sizes in use at PARC .This then is phase I of ubiquitous computing: to construct, deploy, and learn from a computing environment consisting of tabs, pads, and boards. This is only phase I, because it is unlikely to achieve optimal invisibility. (Later phases are yet to be determined). But it is a start down the radical direction, for computer science, away from attention on the machine and back on the person and his or her life in the world of work, play, and home. Hardware Prototypes New hardware systems design for ubiquitous computing has been oriented towards experimental platforms for systems aJnd applications of invisibility. New chips have been less important than combinations of existing components that create experimental opportunities. The first ubiquitous computing technology to be deployed was the Liveboard [Elrod 92], which is now a Xerox product. Two other important pieces of prototype hardware supporting our research at PARC are the Tab and the Pad.

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Tab The ParcTab is a tiny information doorway. For user interaction it has a pressure sensitive screen on top of the display, three buttons underneath the natural finger positions, and the ability to sense its position within a building. The display and touchpad it uses are standard commercial units. The key hardware design problems in the pad are size and power consumption. With several dozens of these devices sitting around the office, in briefcases, in pockets, one cannot change their batteries every week. The PARC design uses the 8051 to control detailed interactions, and includes software that keeps power usage down. The major outboard components are a small analog/digital converter for the pressure sensitive screen, and analog sense circuitry for the IR receiver. Interestingly, although we have been approached by several chip manufacturers about our possible need for custom chips for the Tab, the Tab is not short of places to put chips. The display size leaves plenty of room, and the display thickness dominates total size. Off-theshelf components are more than adequate for exploring this design space, even with our severe size, weight, and power constraints. A key part of our design philosophy is to put devices in everyday use, not just demonstrate them. We can only use techniques suitable for quantity 100 replication, which excludes certain things that could make a huge difference, such as the integration of components onto the display surface itself. This technology, being explored at PARC, ISI, and TI, while very promising, is not yet ready for replication. The Tab architecture is carefully balanced among display size, bandwidth, processing, and memory. For instance, the small display means that even the tiny processor is capable of four frame/sec video to it, and the IR bandwidth is capable of delivering this. The bandwidth is also such that the processor can actually time the pulse widths in software timing loops. Our 23

current design has insufficient storage, and we are increasing the amount of non-volatile RAM in future tabs from 8k to 128k. The tab's goal of postit-notelike casual use puts it into a design space generally unexplored in the commercial or research sector. Pad The pad is really a family of notebook-sized devices. Our initial pad, the ScratchPad, plugged into a Sun SBus card and provided an X-window-systemcompatible writing and display surface. This same design was used inside our first wall-sized displays, the liveboards, as well. Our later untethered pad devices, the XPad and MPad, continued the system design principles of Xcompatibility, ease of construction, and flexibility in software and hardware expansion. As I write, at the end of 1992, commercial portable pen devices have been on the market for two years, although most of the early companies have now gone out of business. Why should a pioneering research lab be building its own such device? Each year we ask ourselves the same question, and so far three things always drive us to continue to design our own pad hardware. First, we need the right balance of features; this is the essence of systems design. The commercial devices all aim at particular niches, and so balance their design to that niche. For research we need a rather different balance, all the more so for ubiquitous computing. For instance, can the device communicate simultaneously along multiple channels? Does the O.S support multiprocessing? What about the potential for high-speed tethering? Is there a high-quality pen? Is there a high-speed expansion port sufficient for video in and out? Is sound in/out and ISDN available? Optional keyboard? Any one commercial device tends to satisfy some of these, ignore others, and choose a balance of the ones it does satisfy that optimize its niche, rather than ubiquitous 24

computing-style

scrap

computing.

The

balance

for

us

emphasizes

communication, ram, multi-media, and expansion ports. Second, apart from balance are the requirements for particular features. Key among these are a pen emphasis, connection to research environments like Unix, and communication emphasis. A high-speed (>64kbps) wireless capability is built into no commercial devices, nor do they generally have a sufficiently high speed port to which such a radio can be added. Commercial devices generally come with DOS or Penpoint, and while we have developed in both, they are not our favorite research vehicles because of lack of full access and customizability. The third thing driving our own pad designs is ease of expansion and modification. We need full hardware specs, complete O.S. source code, and the ability to rip-out and replace both hardware and software components. Naturally these goals are opposed to best price in a niche market, which orients the documentation to the end user, and which keeps price down by integrated rather than modular design. We have now gone through three generations of Pad designs. Six scratchpads were built, three XPads, and thirteen MPads, the latest. The MPad uses an FPGA for almost all random logic, giving extreme flexibility. For instance, changing the power control functions, and adding high-quality sound, was relatively simple FPGA changes. The Mpad has built-in both IR (tab compatible) and radio communication, and includes sufficient uncommitted space for adding new circuit boards later. It can be used with a tether that provides it with recharging and operating power and an ethernet connection. The operating system is a standalone version of the public-domain Portable Common Runtime developed at PARC [Weiser 89].

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The CS of Ubicomp In order to construct and deploy tabs, pads, and boards at PARC, we found ourselves needing to readdress some of the well-worked areas of existing computer science. The fruitfulness of ubiquitous computing for new Computer Science problems clinched our belief in the ubiquitous computing framework. In what follows I walk up the levels of organization of a computer system, from hardware to application. For each level I describe one or two examples of computer science work required by ubiquitous computing. Ubicomp is not yet a coherent body of work, but consists of a few scattered communities. The point of this paper is to help others understand some of the new research challenges in ubiquitous computing, and inspire them to work on them. This is more akin to a tutorial than a survey, and necessarily selective. The areas I discuss below are: hardware components (e.g. chips), network protocols, interaction substrates (e.g. software for screens and pens), applications, privacy, and computational methods. Issues of hardware components In addition to the new systems of tabs, pads, and boards, ubiquitous computing needs some new kinds of devices. Examples of three new kinds of hardware devices are: very low power computing, low-power high-bits/cubicmeter communication, and pen devices. Low Power In general the need for high performance has dominated the need for low power consumption in processor design. However, recognizing the new requirements of ubiquitous computing, a number of people have begun work in using additional chip area to reduce power rather than to increase performance [Lyon 93]. One key approach is to reduce the clocking frequency of their chips 26

by increasing pipelining or parallelism. Then, by running the chips at reduced voltage, the effect is a net reduction in power, because power falls off as the square of the voltage while only about twice the area is needed to run at half the clock speed. Power = CL * Vdd2 * f •

Where CL is the gate capacitance, Vdd the supply voltage, and f the clocking frequency. This method of reducing power leads to two new areas of chip design:

circuits that will run at low power, and architectures that sacrifice area for power over performance. The second requires some additional comment, because one might suppose that one would simply design the fastest possible chip, and then run it at reduced clock and voltage. However, as Lyon illustrates, circuits in chips designed for high speed generally fail to work at low voltages. Furthermore, attention to special circuits may permit operation over a much wider range of voltage operation, or achieve power savings via other special techniques, such as adiabatic switching [Lyon 93]. Wireless A wireless network capable of accommodating hundreds of high speed devices for every person is well beyond the commercial wireless systems planned even ten years out [Rush 92], which are aimed at one low speed (64kbps or voice) device per person. Most wireless work uses a figure of merit of bits/sec x range, and seeks to increase this product. We believe that a better figure of merit is bits/sec/meter3. This figure of merit causes the optimization of total bandwidth throughout a three-dimensional space, leading to design points of very tiny cellular systems.

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Because we felt the commercial world was ignoring the proper figure of merit, we initiated our own small radio program. In 1989 we built spreadspectrum transceivers at 900 MHz, but found them difficult to build and adjust, and prone to noise and multipath interference. In 1990 we built direct frequency-shift-keyed transceivers also at 900 MHz, using very low power to be license-free. While much simpler, these transceivers had unexpectedly and unpredictably long range, causing mutual interference and multipath problems. In 1991 we designed and built our current radios, which use the near-field of the electromagnetic spectrum. The near-field has an effective fall-off of r6 in power, instead of the more usual r2, where r is the distance from the transmitter. At the proper levels this band does not require an FCC license, permits reuse of the same frequency over and over again in a building, has virtually no multipath or blocking effects, and permits transceivers that use extremely low power and low parts count. We have deployed a number of nearfield radios within PARC. Pens A third new hardware component is the pen for very large displays. We needed pens that would work over a large area (at least 60"x40"), not require a tether, and work with back projection. These requirements are generated from the particular needs of large displays in ubiquitous computing -- casual use, no training, naturalness, multiple people at once. No existing pens or touchpad’s could come close to these requirements. Therefore members of the Electronics and Imaging lab at PARC devised a new infrared pen. A camera-like device behind the screen senses the pen position, and information about the pen state (e.g. buttons) is modulated along the IR beam. The pens need not touch the screen, but can operate from several feet away. Considerable DSP and analog design work underlies making these pens effective components of the ubiquitous computing system [Elrod 92].

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Network Protocols Ubicomp changes the emphasis in networking in at least four areas: wireless media access, wide-bandwidth range, real-time capabilities for multimedia over standard networks, and packet routing. A "media access" protocol provides access to a physical medium. Common media access methods in wired domains are collision detection and token-passing. These do not work unchanged in a wireless domain because not every device is assured of being able to hear every other device (this is called the "hidden terminal" problem). Furthermore, earlier wireless work used assumptions of complete autonomy, or a statically configured network, while ubiquitous computing requires a cellular topology, with mobile devices frequently coming on and off line. We have adapted a media access protocol called MACA, first described by Phil Karn, with some of our own modifications for fairness and efficiency. The key idea of MACA is for the two stations desiring to communicate to first do a short handshake of Request-To-Send-N-bytes followed by ClearTo-Send-N-bytes. This exchange allows all other stations to hear that there is going to be traffic, and for how long they should remain quiet. Collisions, which are detected by timeouts, occur only during the short RTS packet. Adapting MACA for ubiquitous computing use required considerable attention to fairness and real-time requirements. MACA (like the original Ethernet) requires stations whose packets collide to back off a random time and try again. If all stations but one back off, that one can dominate the bandwidth. By requiring all stations to adapt the back off parameter of their neighbors we create a much fairer allocation of bandwidth. Some applications need guaranteed bandwidth for voice or video. We added a new packet type, NCTS (n) (Not Clear to Send), to suppress all other 29

transmissions for (n) bytes. This packet is sufficient for a base station to do effective bandwidth allocation among its mobile units. The solution is robust, in the sense that if the base station stops allocating bandwidth then the system reverts to normal contention. When a number of mobile units share a single base station, that base station may be a bottleneck for communication. For fairness, a base station with N > 1 nonempty output queues needs to contend for bandwidth as though it were N stations. We therefore make the base station contend just enough more aggressively that it is N times more likely to win a contention for media access. Two other areas of networking research at PARC with ubiquitous computing implications are gigabit networks and real-time protocols. Gigabitper-second speeds are important because of the increasing number of medium speed devices anticipated by ubiquitous computing, and the growing importance of real-time (multimedia) data. One hundred 256kbps portables per office imply a gigabit per group of forty offices, with all of PARC needing an aggregate of some five gigabits/sec. This has led us to do research into localarea ATM switches, in association with other gigabit networking projects [Lyles 92]. Real-time protocols are a new area of focus in packet-switched networks. Although real-time delivery has always been important in telephony, a few hundred milliseconds never mattered in typical packet-switched applications like telnet and file transfer. With the ubiquitous use of packetswitching, even for telephony using ATM, the need for real-time capable protocols has become urgent if the packet networks are going to support multimedia applications. Again in association with other members of the research community, PARC is exploring new protocols for enabling multimedia on the packet-switched internet [Clark 92]. 30

The internet routing protocol, IP, has been in use for over ten years. However, neither it nor its OSI equivalent, CLNP, provides sufficient infrastructure for highly mobile devices. Both interpret fields in the network names of devices in order to route packets to the device. For instance, the "13" in IP name 13.2.0.45 is interpreted to mean net 13 and network routers anywhere in the world are expected to know how to get a packet to net 13, and all devices whose name starts with 13 are expected to be on that network. This assumption fails as soon as a user of a net 13 mobile device takes her device on a visit to net 36 (Stanford). Changing the device name dynamically depending on location is no solution: higher level protocols like TCP assume that underlying names won't change during the life of a connection, and a name change must be accompanied by informing the entire network of the change so that existing services can find the device. A number of solutions have been proposed to this problem, among them Virtual IP from Sony [Teraoka 91] and Mobile IP from Columbia University [Ioannidis 93]. These solutions permit existing IP networks to interoperate transparently with roaming hosts. The key idea of all approaches is to add a second layer of IP address, the "real" address indicating location, to the existing fixed device address. Special routing nodes that forward packets to the right real address, and keep track of where this address is, are required for all approaches. The internet community has a working group looking at standards for this area (contact [email protected] for more information). Interaction Substrates Ubicomp has led us into looking at new substrates for interaction. I mention four here that span the space from virtual keyboards to protocols for window systems. Pads have a tiny interaction area -- too small for a keyboard, too small even for standard hand printing recognition. Hand printing has the further 31

problem that it requires looking at what is written. Improvements in voice recognition are no panacea, because when other people are present voice will often be inappropriate. As one possible solution, we developed a method of touch-printing that uses only a tiny area and does not require looking. As drawbacks, our method requires a new printing alphabet to be memorized, and reaches only half the speed of a fast typist [Goldberg 93]. Liveboards have a huge interaction area 400 times that of the tab. Using conventional pull down or popup menus might require walking across the room to the appropriate button, a serious problem. We have developed methods of location-independent interaction by which even complex interactions can be popped up at any location. The X window system, although designed for network use, makes it difficult for windows to move once instantiated at a given X server. This is because the server retains considerable state about individual windows, and does not provide convenient ways to move that state. For instance, context and window IDs are determined solely by the server, and cannot be transferred to a new server, so that applications that depend upon knowing their value (almost all) will break if a window changes servers. However, in the ubiquitous computing world a user may be moving frequently from device to device, and wanting to bring windows along. Christian Jacobi at PARC has implemented a new X toolkit that facilitates window migration. Applications need not be aware that they have moved from one screen to another; or if they like, they can be so informed with an up call. We have written a number of applications on top of this toolkit, all of which can be "whistled up" over the network to follow the user from screen to screen. The author, for instance, frequently keeps a single program development and editing environment open for days at a time, migrating its windows back and forth from home to work and back each day. 32

A final window system problem is bandwidth. The bandwidth available to devices in ubiquitous computing can vary from kilobits/sec to gigabits/sec, and with window migration a single application may have to dynamically adjust to bandwidth over time. The X window system protocol was primarily developed for Ethernet speeds, and most of the applications written in it were similarly tested at 10Mbps. To solve the problem of efficient X window use at lower bandwidth, the X consortium is sponsoring a "Low Bandwidth X" (LBX) working group to investigate new methods of lowering bandwidth. [Fulton 93]. Applications Applications are of course the whole point of ubiquitous computing. Two examples of applications are locating people and shared drawing. Ubicomp permits the location of people and objects in an environment. This was first pioneered by work at Olivetti Research Labs in Cambridge, England, in their Active Badge system [Want 92]. In ubiquitous computing we continue to extend this work, using it for video annotation, and updating dynamic maps. For instance, the picture below (figure 3) shows a portion of CSL early one morning, and the individual faces are the locations of people. This map is updated every few seconds, permitting quick locating of people, as well as quickly noticing a meeting one might want to go to (or where one can find a fresh pot of coffee). PARC, EuroPARC, and the Olivetti Research Center have built several different kinds of location servers. Generally these have two parts: a central database of information about location that can be quickly queried and dumped, and a group of servers that collect information about location and update the database. Information about location can be deduced from logins, or collected directly from an active badge system. The location database may be organized to dynamically notify clients, or simply to facilitate frequent polling. 33

Some example uses of location information are: automatic phone forwarding, locating an individual for a meeting, and watching general activity in a building to feel in touch with its cycles of activity (important for telecommuting). PARC has investigated a number of shared meeting tools over the past decade, starting with the CoLab work [Stefik 87], and continuing with video draw and commune [Tang 91]. Two new tools were developed for investigating problems in ubiquitous computing. The first is Tivoli [Pedersen 93], the second Slate, each based upon different implementation paradigms. First their similarities: they both emphasize pen-based drawing on a surface, they both accept scanned input and can print the results, they both can have several users at once operating independently on different or the same pages, they both support multiple pages. Tivoli has a sophisticated notion of a stroke as spline, and has a number of features making use of processing the contents and relationships among strokes. Tivoli also uses gestures as input control to select, move, and change the properties of objects on the screen. When multiple people use Tivoli each must be running a separate copy, and connect to the others. On the other hand, Slate is completely pixel based, simply drawing ink on the screen. Slate manages all the shared windows for all participants, as long as they are running an X window server, so its aggregate resource use can be much lower than Tivoli, and it is easier to setup with large numbers of participants. In practice we have used slate from a Sun to support shared drawing with users on Macs and PCs. Both Slate and Tivoli have received regular use at PARC. Shared drawing tools are a topic at many places. For instance, Bellcore has a toolkit for building shared tools [Hill 93], and Jacobsen at LBL uses multicast packets to reduce bandwidth during shared tool use. There are some commercial products [Chatterjee 92], but these are usually not multi-page and so not really suitable for creating documents or interacting over the course of a 34

whole meeting. The optimal shared drawing tool has not been built. For its user interface, there remain issues such as multiple cursors or one, gestures or not, and using an ink or a character recognition model of pen input. For its substrate, is it better to have a single application with multiple windows, or many applications independently connected? Is packet-multicast a good substrate to use? What would it take to support shared drawing among 50 people, 5,000 people? The answers are likely both technological and social. Three new kinds of applications of ubiquitous computing are beginning to be explored at PARC. One is to take advantage of true invisibility, literally hiding machines in the walls. An example is the Responsive Environment project led by Scott Elrod. This aims to make a building's heat, light, and power more responsive to individually customized needs, saving energy and making a more comfortable environment. A second new approach is to use so-called "virtual communities" via the technology of MUDs. A MUD, or "Multi-User Dungeon," is a program that accepts network connections from multiple simultaneous users and provides access to a shared database of "rooms", "exits", and other objects. MUDs have existed for about ten years, being used almost exclusively for recreational purposes. However, the simple technology of MUDs should also be useful in other, non-recreational applications, providing a casual environment integrating virtual and real worlds [Curtis 92]. A third new approach is the use of collaboration to specify information filtering. Described in the December 1992 issue of Communications of the ACM, this work by Doug Terry extends previous notions of information filters by permitting filters to reference other filters, or to depend upon the values of multiple messages. For instance, one can select all messages that have been replied to by Smith (these messages do not even mention Smith, of course), or all messages that three other people found interesting. Implementing this 35

required inventing the idea of a "continuous query", which can effectively sample a changing database at all points in time. Called "Tapestry", this system provides new ways for people to invisibly collaborate. Privacy of Location Cellular systems inherently need to know the location of devices and their use in order to properly route information. For instance, the traveling pattern of a frequent cellular phone user can be deduced from the roaming data of cellular service providers. This problem could be much worse in ubiquitous computing with its more extensive use of cellular wireless. So a key problem with ubiquitous computing is preserving privacy of location. One solution, a central database of location information, means that the privacy controls can be centralized and so perhaps done well -- on the other hand one break-in there reveals all, and centrality is unlikely to scale worldwide. A second source of insecurity is the transmission of the location information to a central site. This site is the obvious place to try to snoop packets, or even to use traffic analysis on source addresses. Our initial designs were all central, initially with unrestricted access, gradually moving towards controls by individual users on who can access information about them. Our preferred design avoids a central repository, but instead stores information about each person at that person's PC or workstation. Programs that need to know a person's location must query the PC, and run whatever gauntlet of security the user has chosen to install there. EuroPARC uses a system of this sort. Accumulating information about individuals over long periods is both one of the more useful things to do, and also most quickly raises hackles. A key problem for location is how to provide occasional location information for clients that need it while somehow preventing the reliable accumulation of long-term trends about an individual. So far at PARC we have experimented 36

only with short-term accumulation of information to produce automatic daily diaries of activity [Newman 90]. It is important to realize that there can never be a purely technological solution to privacy, that social issues must be considered in their own right. In the computer science lab we are trying to construct systems that are privacy enabled, that can give power to the individual. But only society can cause the right system to be used. To help prevent future oppressive employers or governments from taking this power away, we are also encouraging the wide dissemination of information about location systems and their potential for harm. We have cooperated with a number of articles in the San Jose Mercury News, the Washington Post, and the New York Times on this topic. The result, we hope, is technological enablement combined with an informed populace that cannot be tricked in the name of technology. Computational Methods An example of a new problem in theoretical computer science emerging from ubiquitous computing is optimal cache sharing. This problem originally arose in discussions of optimal disk cache design for portable computer architectures. Bandwidth to the portable machine may be quite low, while its processing power is relatively high, introducing as a possible design point the compression of pages in a ram cache, rather than writing them all the way back over a slow link. The question arises of the optimal strategy for partitioning memory between compressed and uncompressed pages. This problem can be generalized as follows : The Cache Sharing Problem. A problem instance is given by a sequence of page requests. Pages are of two types, U and C (for uncompressed and compressed), and each page is either IN or OUT. A request is served by changing the requested page to IN if it is currently OUT. Initially all pages are 37

OUT. The cost to change a type-U (type-C) page from OUT to IN is CU (respectively, CC). When a requested page is OUT, we say that the algorithm missed. Removing a page from memory is free. Lower Bound Theorem: No deterministic, on-line algorithm for cache sharing can be c-competitive for •

c < MAX (1+CU/(CU+CC), 1+CC/(CU+CC))

This lower bound for c ranges from 1.5 to 2, and no on-line algorithm can approach closer to the optimum than this factor. Bern et al also construct an algorithm that achieves this factor, therefore providing an upper bound as well. They further propose a set of more general symbolic programming tools for solving competitive algorithms of this sort. •

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SMART-ITS PLATFORM You can think of a Smart-Its as a small, self-contained, stick-on computer that users can attach to objects much like a 3M Post-It note. To ensure flexibility, we used a modular approach when designing the hardware. A Smart-Its consists of a core board with a wireless transceiver to let the device communicate with other Smart- Its, plus a sensor board that gives the Smart-Its data about its surroundings. For more information about the Smart-Its architecture, see “The Smart-Its Hardware” sidebar. The standard sensor board has five sensors: light, sound, pressure, acceleration, and temperature. For specific purposes, we could add other sensors—such as a gas sensor, a load sensor, or a camera for receiving images. We have also developed several APIs to aid application development. For instance, there is a communication API to facilitate communication between Smart-Its and other devices.

Another

example is the perception API, which allows the abstraction of low-level sensor data to higher-level concepts, so-called percepts. The major advantage of the Smart-Its platform is that it allows designers and researchers to construct responsive or intelligent environments with comparably little overhead. Typically, research projects that develop smart or context-aware objects require building a lot of custom hardware and software from scratch. The Smart-Its project addresses this issue by presenting a standardized hardware solution coupled with communication and sensing APIs. Future interactive systems examples:-

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The A-Life system uses an Oximeter and other sensors to provide rescue teams with updated information about avalanche victims.

The rescue team’s interface is PDA based and gives instant access to vital information to aid in their work.

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Together, the items in the smart restaurant installation created an interactive environment where visitors could interact with smart objects.

System Software for Ubiquitous Computing Ubiquitous computing, or ubicomp, systems designers embed devices in various physical objects and places. Frequently mobile, these devices— such as those we carry with us and embed in cars—are typically wirelessly networked. Some 30 years of research have gone into creating distributed computing systems, and we’ve invested nearly 20 years of experience in mobile computing. With this background, and with today’s developments in miniaturization and wireless operation, our community seems poised to realize the ubicomp vision. However, we aren’t there yet. Ubicomp software must deliver functionality in our everyday world. It must do so on failure-prone hardware with limited resources. Additionally, ubicomp software must operate in conditions of radical change. Varying physical circumstances cause 41

components routinely to make and break associations with peers of a new degree of functional heterogeneity. Mobile and distributed computing research has already addressed parts of these requirements, but a qualitative difference remains between the requirements and the achievements. In this article, we examine today’s ubiquitous systems, focusing on software infrastructure, and discuss the road that lies ahead. Characteristics of ubiquitous systems We base our analysis on physical integration and spontaneous interoperation, two main characteristics of ubicomp systems, because much of the ubicomp vision, as expounded by Mark Weiser and others, either deals directly with or is predicated on them. Physical integration An ubicomp system involves some integration between computing nodes and the physical world. For example, a smart coffee cup, such as a Media- Cup, serves as a coffee cup in the usual way but also contains sensing, processing, and networking elements that let it communicate its state (full or empty, held or put down). So, the cup can give colleagues a hint about the state of the cup’s owner. Or consider a smart meeting room that senses the presence of users in meetings, records their actions, and provides services as they sit at a table or talk at a whiteboard. The room contains digital furniture such as chairs with sensors, whiteboards that record what’s written on them, and projectors that you can activate from anywhere in the room using a PDA (personal digital assistant).Human administrative, territorial, and cultural considerations mean that ubicomp takes place in more or less discrete environments based, for example, on homes, rooms, or airport lounges. In other words, the world consists of ubiquitous systems rather than “the ubiquitous system.” So, from physical integration, we draw our Boundary Principle: Ubicomp system designers should divide the ubicomp world into environments with boundaries 42

that demarcate their content. A clear system boundary criterion—often, but not necessarily, related to a boundary in the physical world—should exist. A boundary should specify an environment’s scope but doesn’t necessarily constrain interoperation. Figure:

The ubiquitous computing world comprises environments with boundaries and components appearing in or moving between them.

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Spontaneous interoperation In an environment, or ambient, there are components—units of software that implement abstractions such as services, clients, resources, or applications (see Figure). An environment can contain infrastructure components, which are more or less fixed, and spontaneous components based on devices that arrive and leave routinely. Although this isn’t a hard and fast distinction, we’ve found it to be useful. In a ubiquitous system, components must spontaneously interoperate

in

changing

environments.

A

component

interoperates

spontaneously if it interacts with a set of communicating components that can change both identity and functionality overtime as its circumstances change. A spontaneously interacting component changes partners during its normal operation, as it moves or as other components enter its environment; it changes partners without needing new software or parameters. Rather than a de facto characteristic, spontaneous interoperation is a desirable ubicomp feature. Mobile

computing

research

has

successfully

addressed

aspects

of

interoperability through work on adaptation to heterogeneous content and devices, but it has not discovered how to achieve the interoperability that the breadth of functional heterogeneity found in physically integrated systems requires. For a more concrete definition, suppose the owners of a smart meeting room propose a “magic mirror,” which shows those facing it their actions in the meeting. Ideally, the mirror would interact with the room’s other components from the moment you switch it on. It would make spontaneous associations with all relevant local sources of information about users. As another example, suppose a visitor from another organization brings his PDA into the room and, without manually configuring it in any way, uses it to send his presentation to the room’s projector. We choose spontaneous rather than the related term ad hoc because the latter tends to be associated with networking—

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adhoc networks are autonomous systems of mobile routers. But you cannot achieve spontaneous interoperation as we have defined it solely at the network level. Also, some use ad hoc to mean infrastructure free. However, ubicomp involves both infrastructure-free and infrastructure enhanced computing. This includes, for example, spontaneous interaction between small networked sensors such as particles of smart dust, separate from any other support, or our previous example of a PDA interacting with infrastructure components in its environment. From spontaneous interoperation, we draw our Volatility Principle: You should design ubicomp systems on the assumption that the set of participating users, hardware, and software is highly dynamic and unpredictable. Clear invariants that govern the entire system’s execution should exist. The mobile computing community will recognize the Volatility Principle in theory, if not by name. However, research has concentrated on how individual mobile components adapt to fluctuating conditions. Here, we emphasize that ubicomp adaptation should involve more than “every component for itself” and not restrict itself to the short term; designers should specify system-wide invariants and implement them despite volatility. Examples The following examples help clarify how physical integration and spontaneous interoperation characterize ubicomp systems. Our previous ubicomp example of the magic mirror demonstrates physical integration because it can act as a conventional mirror and is sensitive to a user’s identity. It spontaneously interoperates with components in any room. Non examples of ubicomp include: 1. Accessing email over a phone line from a laptop. This case involves neither physical integration nor spontaneous inter operation; the laptop maintains the same association to a fixed email server. 45

This exemplifies a physically mobile system: it can operate in various physical environments but only because those environments are equally transparent to it. A truly mobile (although not necessarily ubiquitous) system engages in spontaneous interactions. 2. A collection of wirelessly connected laptops at a conference. Laptops with an IEEE 802.11 capability can connect spontaneously to the same local IEEE 802.11 network, assuming no encryption exists. Laptops can run various applications that enable interaction, such as file sharing. You could argue this discovery of the local network is physical integration, but you’d miss the essence of ubicomp, which is integration with that part of the world that has a non electronic function for us. As for spontaneous interaction, realistically, even simple file sharing would require considerable manual intervention. 3. A smart coffee cup and saucer. Our smart coffee cup (inspired by but different from the Media Cup) clearly demonstrates physical integration, and it demonstrates a device that you could only find in a ubiquitous system. However, if you constructed it to interact only with its corresponding smart saucer according to a specialized protocol, it would not satisfy spontaneous interoperation. The owner couldn’t use the coffee cup in another environment if she forgot the saucer, so we would have localization instead of ubiquitous functionality. 4. Peer-to-peer games. Users play games such as Pirates! with portable devices connected by local area wireless network. Some cases involve physical integration because the client devices have sensors, such as proximity sensors in Pirates! Additionally, some games can discover other players over the local network, and this dynamic association between the players’ devices resembles 46

spontaneous interaction. However, such games require preconfigured components. A more convincing case would involve players with generic game-playing “pieces,” which let them spontaneously join local games even if they had never encountered them before. 5. The Web The Web is increasingly integrated with the physical world. Many devices have small, embedded Web servers, and you can turn objects into physical hyperlinks—the user is presented with a Web page when it senses an identifier on the object. Numerous Web sites with new functionality (for example, new types of e- sites) spring up on the Web without, in many cases, the need to reconfigure browsers. However, this lacks spontaneous interoperation— the Web requires human supervision to keep it going. The “human in the loop” changes the browser’s association to Web sites. Additionally, the user must sometimes install plug-ins to use a new type of downloaded content. Software challenges Physical integration and spontaneous interoperation have major implications for software infrastructure. These ubicomp challenges include a new level of component interoperability and extensibility, and new dependability guarantees, including adaptation to changing environments, tolerance of routine failures or failure like conditions, and security despite a shrunken basis of trust. Put crudely, physical integration for system designers can imply “the resources available to you are sometimes highly constrained,” and spontaneous interoperation means “the resources available to you are highly dynamic but you must work anywhere, with minimal or no intervention.” Additionally, an ubicomp system’s behavior while it deals with these issues must match users’ expectations of how the physical world behaves. This is extremely challenging because users don’t think of the physical world

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as a collection of computing environments, but as a collection of places with rich cultural and administrative semantics. The semantic Rubicon Systems software practitioners have long ignored the divide between system- and human-level semantics. Ubicomp removes this luxury. Little evidence exists to suggest that software alone can meet ubicomp challenges, given the techniques currently available. Therefore, in the short term, designers should make clear choices about what system software will not do, but humans will. System designers should pay careful, explicit attention to what we call the semantic Rubicon of ubiquitous systems (see Figure). (The historical Rubicon river marked the boundary of what was Italy in the time of Julius Caesar. Caesar brought his army across it into Italy, but only after great hesitation.) The semantic Rubicon is the division between system and user for high-level decision-making or physical world semantics processing. When responsibility shifts between system and user, the semantic Rubicon is crossed. This division should be exposed in system design, and the criteria and mechanisms for crossing it should be clearly indicated. Although the semantic Rubicon might seem like a human- computer interaction (HCI) notion, especially to systems practitioners, it is, or should be, a ubicomp systems notion. Figure:

The semantic Rubicon demarcates responsibility for decision making between the system and the user; allocation between the two sides can be static or dynamic.

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REFERENCES

1. Mark Weiser Article from Georgia tech future computing environment. 2. www.google.com 3. wikiepedia.com

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