1. Laboratory for Communications Engineering Engineering Department, University Of Cambridge N E T W O R K E D S U R F A C E S Frank Hoffmann and James Scott {fh215, jws22}@cam.ac.uk http://www-lce.eng.cam.ac.uk/

2. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Introduction The Laboratory for Communications Engineering In the Engineering Department at Cambridge University Founded 2 years ago by Professor Andy Hopper Strong links with industry, including AT&T Labs Cambridge, where Andy is MD Frank Hoffmann and James Scott 3rd year PhD students From Electronics and Computer Science backgrounds respectively Advisors at AT&T Labs: Mike Addlesee and Glenford Mapp JamesFrankGlenfordMikeAndy

3. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Networked Surfaces Provide network connectivity using physical surfaces Such as desks, floors, etc. All devices are surface-bound due to gravity: lets make use of this! No 'plug', no special position/alignment required Provides near-total mobility for non-wearable devices Uses precise “topology” of metal pads to achieve this Supports a range of services Ethernet-style inter-computer networks Slower serial busses for peripherals Power Other devices

4. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Wired vs Wireless vs Surface Physical MediumWired networkWireless network Networked Surface BandwidthHighLimited High (though not quite as good as a shielded wire) Multi-Access Dedicated Connections Possible Intrinsically Shared Medium Dedicated Connections Possible MobilityTethered3D-Free Surface-based “2D-Free” Power Can easily be provided Hard to provide Can be provided, with safety concerns

5. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Example App: Networked Desk Get rid of “spaghetti” behind desks and of need for trunking everywhere Eliminates possibility of mis-wiring Novices don’t want to know what a “serial port” is c.f. Ubiquitous Computing Power provided as low voltage DC With current limiting hardware No danger to humans Most devices do not use mains-level AC anyway

6. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Tile Controller Tile Controller F U N C T I O N B U S S E S T I L E C O N T R O L B U S Surface Manager (keeps track of objects, allocates resources, controls tiles) Object Controller To other networks Object e.g. Palm Pilot Computer Keyboard Mobile phone etc System Architecture Handshaking Data Traffic

7. Laboratory for Communications Engineering Engineering Department, University Of Cambridge F U N C T I O N B U S S E S T I L E C O N T R O L B U S Tile Controller Tile Controller Surface Manager (keeps track of objects, allocates resources, controls tiles) To other networks Object Controller Object e.g. Palm Pilot Computer Keyboard Mobile phone etc System Architecture Handshaking Data Traffic

8. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Prototype Surface Pads Tile Controller Object Pads Object Controller Function Busses Tile Control Bus PCI Interface to PC acting as Surface Manager Power for Tile Controllers

9. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Topology Tile Controller Tile Controller F U N C T I O N B U S S E S T I L E C O N T R O L B U S Surface Manager (keeps track of objects, allocates resources, controls tiles) Object Controller To other networks Object e.g. Palm Pilot Computer Keyboard Mobile phone etc

10. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Topology Arrangement of metal pads with: –Rectangular strips on Surface –Circular pads, themselves in a circle, on Object –Surface gaps bigger than object pads hence no shorts Connects regardless of object location proven mathematically and in computer simulations Minimises number of pads required and hence the amount of controlling circuitry Could be implemented invisibly conducting paints, novel materials...

11. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Tile Controller Tile Controller F U N C T I O N B U S S E S T I L E C O N T R O L B U S Surface Manager (keeps track of objects, allocates resources, controls tiles) Object Controller To other networks Object e.g. Palm Pilot Computer Keyboard Mobile phone etc Tile Controller

12. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Tile Controller Each tile is controlled by a microprocessor (  P) An analogue mux connects each strip to either a function bus or the  P handshaking lines The muxes are controlled through a FPGA Handshaking is done by  P until a connection is established PIC Micro- Processor FPGA Mux Strip Handshaking In/Out Mux Control Control Bus Function Busses

13. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Tile Controller Tile Controller F U N C T I O N B U S S E S T I L E C O N T R O L B U S Surface Manager (keeps track of objects, allocates resources, controls tiles) Object Controller To other networks Object e.g. Palm Pilot Computer Keyboard Mobile phone etc Handshaking

14. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Handshaking “Handshaking” = finding and connecting new objects Distributed on surface-side to tile controllers Object asks for functions from the surface E.g. high speed data bus, low speed data bus, power Different surfaces might have different functions available When connection is finalised,tile and object controllers play no further role And therefore do not have to “understand” the signals sent on the busses

15. Laboratory for Communications Engineering Engineering Department, University Of Cambridge TX RX GND Tile Controller Tile Control Bus TX RX GND Object Controller Handshaking Protocol in Action Beacons Beacon Request “TX” Beacon Ack “TX” Beacon Request “TX” Connection on StandbyMany Connections on Standby Standby Beacon Confirm Standby Beacon Confirmed ConnectionConfirmed Connections “New Object” message sent to Surface Manager

16. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Tile Controller Tile Controller F U N C T I O N B U S S E S T I L E C O N T R O L B U S Surface Manager (keeps track of objects, allocates resources, controls tiles) Object Controller To other networks Object e.g. Palm Pilot Computer Keyboard Mobile phone etc Surface Busses

17. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Surface Busses All busses must be true multi-drop i.e. not Ethernet, which nowadays is hubbed Low speed devices are catered for with I 2 C RS-232 data can be packaged easily over I 2 C, using the handshaking  P High speed bus uses B-LVDS differential modulation Differential scheme better for signal quality in noisy environment Multiple B-LVDS busses are provided this provides more bandwidth, and allows QoS to be supported

18. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Surface Manager Tile Controller Tile Controller F U N C T I O N B U S S E S T I L E C O N T R O L B U S Surface Manager (keeps track of objects, allocates resources, controls tiles) Object Controller To other networks Object e.g. Palm Pilot Computer Keyboard Mobile phone etc

19. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Surface Manager Hardware is a PCI card using a PCI bridge chip and a FPGA Software is a PCI device driver under Linux FPGA has control engines for each surface bus Small FIFO’s inside FPGA buffer data in and data out for each bus Soft- ware Driver PCI Bus PCI Bridge Ctrl I 2 C Data I 2 C B-LVDS A B-LVDS B B-LVDS C I2C Driver B-LVDS Driver I2C Driver B-LVDS Driver B-LVDS Driver Status & Control

20. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Tile Controller Tile Controller F U N C T I O N B U S S E S T I L E C O N T R O L B U S Surface Manager (keeps track of objects, allocates resources, controls tiles) Object Controller To other networks Object e.g. Palm Pilot Computer Keyboard Mobile phone etc Data Transport Data Traffic

21. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Data Transport Low bandwidth devices: Present as “virtual” serial ports e.g. Palm Pilot, keyboard, modem High bandwidth devices: Will have TCP/IP stacks But TCP performs badly in presence of disconnection It wrongly assumes losses are due to congestion, and backs off Could modify TCP to include “Disconnected” state Instead, make link layer “smart”, by re-sending packets on behalf of TCP when connections are re-established “Kicks” TCP into action, without waiting for exponential timeout Saves having to re-implement TCP for every object Mobile IP/IPv6 can handle movement between surfaces

22. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Conclusions Prototypes are currently at systems integration stage Object discovery and connection found to be ~300ms Doesn’t matter if we disconnect and reconnect once in a while Preliminary results show LVDS bus speeds ~ megabits Advantages Mobility – Currently “wired” devices can become 2D-mobile Convenience – No need to carry wiring around Ubiquity – Common interface for many network types

23. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Directions for the Future Sentient Computing –Can discover location and orientation of each object –Could implement networked sensors easily –The desk itself becomes an interface Physical Transmission Medium –Could use capacitive coupling to avoid direct wire interface –Could use inductive coupling for ultra-safe provision of power

24. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Question Time! (FAQ Below) Q: Your diagram/statement on slide X is wrong A: Well done for catching the deliberate error Q: Will it work? A: Yes Q: Back that up A: Next question please

25. Laboratory for Communications Engineering Engineering Department, University Of Cambridge Thanks for listening! To get in touch: Frank Hoffmann and James Scott {fh215, jws22}@cam.ac.uk http://www-lce.eng.cam.ac.uk/