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/

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N E T W O R K E DS U R F A C E SFrank
Hoffmann and James Scott fh215,
jws22_at_cam.ac.ukhttp//www-lce.eng.cam.ac.uk/
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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 ATT Labs
  Cambridge, where Andy is MD
• Frank Hoffmann and James Scott
• 3rd year PhD students
• From Electronics and Computer Science backgrounds
  respectively
• Advisors at ATT Labs Mike Addlesee and Glenford
  Mapp

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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

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Wired vs Wireless vs Surface
Physical Medium Wired network Wireless network Networked Surface
Bandwidth High Limited High (though not quite as good as a shielded wire)
Multi-Access Dedicated Connections Possible Intrinsically Shared Medium Dedicated Connections Possible
Mobility Tethered 3D-Free Surface-based 2D-Free
Power Can easily be provided Hard to provide Can be provided, with safety concerns
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Example App Networked Desk

• Get rid of spaghetti behind desks
• and of need for trunking everywhere
• Eliminates possibility of mis-wiring
• Novices dont 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

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System Architecture
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System Architecture
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Prototype
Surface Pads
Power for Tile Controllers
Tile Controller
Function Busses
Object Pads
Tile Control Bus
Object Controller
PCI Interface to PC acting as Surface Manager
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Topology
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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...

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Tile Controller
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Tile Controller

• Each tile is controlled by a microprocessor (mP)
• An analogue mux connects each strip to either a
  function bus or the mP handshaking lines
• The muxes are controlled through a FPGA
• Handshaking is done by mP until a connection is
  established

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Handshaking
Handshaking
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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

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Handshaking Protocol in Action
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Surface Busses
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Surface Busses

• All busses must be true multi-drop
• i.e. not Ethernet, which nowadays is hubbed
• Low speed devices are catered for with I2C
• RS-232 data can be packaged easily over I2C,
  using the handshaking mP
• 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

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Surface Manager
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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 FIFOs inside FPGA buffer data in and data
  out for each bus

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Data Transport
Data Traffic
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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

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Conclusions

• Prototypes are currently at systems integration
  stage
• Object discovery and connection found to be
  300ms
• Doesnt 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

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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

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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

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Thanks for listening!To get in touchFrank
Hoffmann and James Scott fh215,
jws22_at_cam.ac.ukhttp//www-lce.eng.cam.ac.uk/