Zerox ParcTab(The ParcTab Ubiqitous computing Experiment, Roy Want, Bill N. Schilit, Norman I. Adams, Rich Gold, Karin Petersen, David Goldberg, John R. Ellis, Mark WeiserXerox Palo Alto Research Center, Palo Alto, California, USA, 1995) Hoon OhUniversity of Ulsan
Table of Contents • Introduction - Ubiquitous Computing • PARCTAB System Design • User-Interface Design for Palm-Sized Computers • PARCTAB System Architecture • Developing System and Application Components • A Classification of PARCTAB Application • Experiences with the PARCTAB System • Conclusion
Introduction - Ubiquitous Computing • ParcTab system? • Palm-sized mobile computer into office network • Testbed for Ubiquitous Computing that enriches computing environment by emphasizing context sensitivity, casual interaction, and the spatial arrangement of computers
Context Information • Mobile computing + Context Communication => Powerful Computing Environment • Contexts • The name of the user’s location; • The identities of the user and of other people nearby; • The identities and status of the nearby printers, workstations, Liveboards, coffee machines, etc.; • Physical parameters such as time, temporature, light level, and weather condition.
Used Devices • Inch scale devices easily attached to clothing or carried in a pocket or hand. • Foot-sized devices carried, though probably not all the time. • Personal Notebooks • Other notepads scattered throughout the work environment and can be used by anyone • Computers with yard-sized screens like whiteboards inch-size always attached PARCTAB foot-size particularly carried PARCPAD yard-size stationary Liveboard
One Possible Senario • Consider an employee who wants to show a set of figures to his manager. • As he approaches her office, a quick glance at his tab confirms that the boss is in and alone. In the midst of their conversation, the employee uses the tab to locate the data file on the network server and to request a printout. The system sends his request by default to the closest printer and notifies him when the job is finished.
Goals for the PARCTAB project • To design a mobile hardware device, the PARCTAB, that enables personal communication; • To design an architecture that supports mobile computing; • To construct context-sensitive applications that exploit this architecture; • To test the entire system in an office community of about 41 people acting as both users and developers of mobile applications.
PARCTAB System Design (1) • Hardware Design Goals • everyday accessory • reliable wireless connectivity • detection of current location to the resolution of a room • at least one day battery life • Even with only one free hand, It should be used. • Electronic Ink
PARCTAB System Design (2) • Design limitation • Cost • Weight, processor performance, Communication bandwidth, display resolution, and bandwidth vs. battery life • Ergonomic package • production-quality custom plastic case with a removable belt clip • For rither one-handed use or two-handed use • Two-handed: Touch screen with Stylus • 3 buttons • Symmetric and rotation of display
IR Detectors IR Emitters PARCTAB transceiver PARCTAB System Design (3) • Communication - Infrared • Easier to design a cellular system • Room-sized cell (nanocell) => low power consumption • more secured • More pin down a user’s location precisely • Transceiver Design • Coding and decoding infrared packets; • Buffering data; • Attached to a ceiling; • 20 feet radius cell; • Connect to LAN through RS-232 port of nearby workstation; and • 9600 or 19200 baud
PARCTAB System Design (4) • Transmission Control • IR detectors have difficulty tuning narrow frequency ranges => TDMA • IR medium like a bus • CSMA method • Link-layer packet acknowledgement
Packet • Packet type: define the speed of transmission • Length • Uplink: 14 bytes, downlink: 247 bytes • CS: checksum
Acknowledgement • No Ack => resends the same packet a number of times • If a ParcTab is exposed to two rooms, both cell tranceivers might ack…corrupting ack signal • Transceivers are assigned different addresses • Only acknowledges the packets addressed to them
Why need a special user interface? • ParcTAB’s 128 x 64 pixel monochrome display • How to select, display, and enter information in a very limited space?
User-Interface Design for Palm-Sized Computers(1) • Buttons vs. Touch Screen • Alternative way • Cooperating way • Text Entry • Onscreen keyboards • Unistrokes vs. Graffiti Possible solution: On clicking the middle push button, a menu of commands pops up. The top and bottom buttons then move the cusor up and down, while a second click of the middle button selects the command on which the cusor currently rests.
User-Interface Design for Palm-Sized Computers(2) • Elision Method • Divide and Conquer style search • Incremental Searches • With each letter entered, the application narrows the list.
PARCTAB System Architecture(1) • Use the tab like a graphical terminal • With a few exceptions • Taking notes by using Unistrokes • Downloaded file viewer Workstation-based
PARCTAB System Architecture(2) • Tab Agent • Actual ParcTAB processes on network machine • Get all messages from applications and also from the tab • IR Gateway • gateway process on the IR transceiver-attached workstation • T-RPC • A set of procedures that application developer can use. • Format of IR packet data payload
T-RPC call and Event Notification T-RPC Functions: display_text, display_bits, generate_tones, set_epoch and wake_up
Developing System and Application Components • Modula-3 • PARCTAB’s system software • relatively new language • good at threads and RPC • programming environment lacked for debugging. • Tcl/Tk • MacTabbit
A Classification of PARCTAB Application (1) • Various Contexts • location, time, presence of people... • Information Access • Organizer, Context-Sensitive file viewer.. • Communication • E-Mail, Locator & Pager.. • Computer Supported Collaboration • Group Pointing (with Liveboard), Voter, Multi-tab Virtual Paper...
A Classification of PARCTAB Application (2) • Remote Control • With Responsive Environment project • Local data/application
Experiences with the PARCTAB System • The Experimental Network at PARC • Mar ’93 with 20 users • April ’94 with 41 users • Infrared Interference • Usage Data • Popular Application (mail, weather, network file browser, local file loader...) • Application Using Time (mail, Unistroke tutor, writer, file browser…) • When, Where, How Long?
Conclusion • Combination of portability with information about context • but not very useful without network • Bandwidth limitation problem • Characteristics of User Generated Traffic • Factors Affecting Acceptance • Importance of User Interface • Popular Applications • Benefits • Future works