1. Challenges of Mobile Computing [Forman & Zahorjan, 1994] Wireless Communication –Disconnection –Low Bandwidth –High bandwidth variability –Heterogenous network –Security

2. Mobility –Address migration –Location-dependent information –Migrating locality Portability –Power consumption (see Table 1) –Form factor –Small user interface and storage capacity –Risks to data and physical damage

3. Xerox PARCTAB A first attempt at a thin handheld client for ubiquitous computing – office environment

4. Ubiquitous Computing Philosophy Demand less of our attention than current computers Advantages of an intelligently orchestrated and highly connected system. Context-aware features –User’s current location –Identities of user and nearby people –Identities and status of nearby resources –Physical parameters (time, temperature, …)

5. PARCTAB Design Goals Small, light and aesthetically pleasing Reliable wireless connectivity Tracking mechanism to know its location (resolution of a room) Run on batteries for atleast one day without recharging Allow casual interaction (even with one hand) Display graphics & text, touch-screen Reasonable cost of hardware and network

6. Hardware (1995!) 12 MHz, 8-bit Intel 87C524 Microcontroller (with low power modes) 128 KB memory 2.4in*1.8in LCD (128*64 monochrome pixels) Buttons + Touch-screen 215g in weight (battery is 70g) Consumes 27mA at 5V (normal) and 30uA (low power mode) – needs only around 1 charge per week (around 400 minutes)

7. Communication Space and power constraints – Infrared (IR) 9600/19200 baud IR signals are contained by walls One transceiver per room (cell) Transceiver is connected to RS-232 port of a workstation in the room (which is on a LAN)

8. Transceiver Coverage around 20ft radius Performs transmission, receiving, coding, decoding, buffering, protocol checks. Transmission: 2 dozen IR emitters placed at 15 degree intervals Reception: 2 detectors provide 360 degree coverage

9. Transmission Control Time division multiplexing of medium CSMA protocol to provide access to IR channel with exponential backoff when busy. Ack needed bit in Type forcing explicit acknowledgements 1144 3-247 2 Type Len. Dest. Src. Payload CS

10. User Interface Buttons + Touch-screen Keyboard entry + Unistrokes Display can only show 8 lines of 21 characters Elision and incremental searches

11. Software Architecture Tab1 Tab4 Tab3 Tab2 Transceiver Gateway Tab1 Agent Tab2 Agent Tab3 Agent Tab4 Agent Video Shell Locate Calendar Shell Mail Vote Shell IR Ethernet RS232

12. Tabs resemble dumb terminals Execute simple local functions in response to remote procedure calls (RPCs) There is one tab agent for each tab that maintains current info. (eg location) Request from application comes to agent, which forwards to appropriate gateway, which then sends it to transceiver on RS- 232 to be broadcast using IR Events from tab are sent to the appropriate agent in the reverse direction

13. Simple tab functions (displaytext, displaybitmap, generatetones, wakeup, etc) Generates beacon events every 30 secs for location Gateway uses a name service to locate tab agent Appends a return address and location id to the agent A centralized location service keeps track of each tab’s location that is updated by tab agent

14. Example Applications Information access –Weather forecast, dictionary, thesaurus, file browser, WWW, Diary (of day’s activities) Communication –Mail, locator, pager Media applications Computer supported collaboration –Group pointing, voting, … Remote Control

15. The InfoPad Mutimedia Terminal For wireless information access and display of multimedia data Again a very thin client – does only wireless communication and I/O processing It is like a switch between the backend and the I/O devices

16. InfoPad Hardware Wireless Network Interface (FPGA) Speech Codec Display Video Decomp Keyboard, Pointer Other I/O Processor ARM60 10MHz 512K RAM, 128K ROM

17. Power breakdown (9.6Watts)