An Integrated approach to developing sensor network solutions

1
An Integrated approach to developing sensor
network solutions

• Presented by
• Richie John Thomas
• 08/27/04

2
Introduction

• Paper on the development work on sensor networks
  at Computer and Network Architecture Lab. Of the
  Swedish Institute of Computer Science
• System core
• ESB Sensor Hardware running the Contiki OS
• Contiki emulation/simulation enviornment for
  development

3

• Communication Stack
• Adaptive energy efficient MAC
• TCP/IP layer optimized for resource constrained
  devices allows system to be connected to
  internet system

4
Hardware Platform

• ESB (Embedded sensor board)
• Texas Instruments MSP 430 low power micro
  controller
• RF monolithics TR 1001 single chip RF transceiver
• Collection of sensors
• Light- visible light
• Passive infra red-movement
• Temperature
• Vibration-movement of sensor board
• Microphone-ambient noise level
• Infra red sender and receiver

5

• MSP 430 has 60 kb flash ROM and 2kb RAM
• 32 kb EEPROM provides addl. Persistent sec.
  storage
• RF transceiver operates at 868 MHz and supports
  rates upto 115.2 kbps
• Board has two external Connectors
• RS 232 port for communication with PC
• JTAG interface code downloading and debugging

6

• MSP 430 for low power appln.
• Provides sleep modes awakened by interrupts from
  internal timers or sensors
• Supports selective rewriting of internal flash
  ROM
• TR 1001 RF transceiver
• Baseband transmission with either amplitude shift
  keying or on-off keying
• Provides half duplex bit level access to physical
  radio medium

7

• Higher level mechanisms (MAC protocol processing,
  data encoding, time multiplexing) should be done
  in s/w
• Transceiver connected to one of MSP 430 UART-Bit
  shifting in h/w rather than s/w
• UART causes interrupt only after full 8 bit
  received as against MICA motes where interrupt
  for each incoming bit

8
The embedded sensor board
9
The Contiki OS

• Flexible- allows individual programs and services
  to be dynamically loaded and unloaded in a
  running system.
• Based on event based concurrency model
• But also provides preemptive multithreading
• Event based systems have lower resource
  requirements and well suited for sensor networks

10

• Allows cryptographic computations as it can be
  run on a separate thread
• Allows dynamic reprogramming of n/w behavior
  due to service layer
• Conceptual layer providing service discovery and
  run-time dynamic service replacement

11

• Portability makes it trivial to run Contiki as a
  user level process under different PC OS
• Appln. pgms developed in simulator can be
  directly run and compiled on the sensor h/w

12
MAC Layer

• Plays key role in energy efficiency and quality
  of service
• MAC layer under development
• Energy efficient TDMA-like structure overlaid on
  CSMA based collision avoidance protocol
• Asynchronous Meet requirements on size,
  complexity and cost and deployment in extreme
  environment with variable h/w stability

13

• Lightweight
• No traffic overhead- foregoing synchronization
• Scalable for multihop sensor n/w-no centralized
  coordination used
• Provide good best effort QoS
• Energy efficiency
• Asynchronous power save protocol
• Based on the observation if node awake for just
  over half of the time is awake interval will
  overlap with that of each of its neighbors
• Nodes can determine available transmission window
  of neighbors
• Node sleeps when no transmission

14

• Flow adaptation
• Phase adjustment used to increase effective
  capacity of a region and reduce latency
• Node adjust its phase to avoid sending data when
  there are high levels of contention or
  interference
• Sequence of nodes forming a path can adjust their
  phase to minimize intra path interference

15
TCP/IP for Sensor Networks

• This requirement for network management,
  calibration, diagnostics, debugging
• Possible to connect network directly to Internet
• Sensor data is transmitted using UDP/IP but for
  administrative tasks reliable unicast connections
  required

16

• TCP/ IP used
• Individual nodes can be addressed and necessary
  reprogramming of sensors performed
• Also for debugging and diagnostic tasks requiring
  reliable connectivity to a specific sensor
• uIP has been developed with size of few kb and
  few hundred bytes of RAM not only on ESB but
  variety of 8 and 16 bit processors

17

• Spatial IP addressing
• Each node uses its spatial location to construct
  its IP address
• The spatial IP address only denotes the location
  and not single identifiable node
• If node replaced new node given same IP address
  as replaced node
• Nodes aware of their spatial location neither
  require central server or communication between
  nodes for address assignment

18
(No Transcript)
19

• Distributed TCP Caching
• Packet loss result in heavy overhead due to TCP
  end to end ack. and retransmission scheme
• Poor performance in energy consumption and
  throughput
• DTC cache TCP segments in network and perform
  local retransmissions
• Nodes are allowed to cache only one segment
• Nodes attempt to identify and cache segments not
  received by next hop

20

• The segment lost i.e. for which no ack. has been
  received is locked in cache
• DTC has to respond to lost packets more quickly
  to avoid end-to-end transmissions
• DTC uses ordinary TCP mechanisms to detect packet
  loss
• Analytical and simulation results indicate that
  DTC increases TCP performance
• DTC currently being implemented in ESB nodes
  using Contiki simulator

21
Applications

• Building security
• Unwarranted motion in the secured building
  notified via GSM and security personnel logs into
  the building network to obtain status
• Two functions for sensor nodes- motion detectors
  and backbone nodes
• Motion detectors in rooms and backbone nodes
  along corridor
• Motion detectors has direct comm. path with at
  least one backbone node and each backbone node
  had contact with one other backbone node

22

• One backbone node equipped with external
  interface device
• Alarm from motion detector to its backbone node
  and from there to its back bone node
• Eventually all backbone nodes have info. abt.
  entire state of network
• Security team with mobile backbone node to scan
  the information
• Uses spatial IP addressing but mobile backbone
  node has fixed IP address from another n/w to
  differentiate it from other backbone nodes

23

• Marine monitoring
• Used to study water temp. and salinity
• Sensors attached to a buoy takes measurements at
  known depths
• These connected as fixed network as communication
  expensive
• Above waterline on the buoy is a full function
  ESB
• These collect data from fixed n/w below and
  transfer over wireless interface to gateway node
• From here by GPRS to marine sciences center

24

• This gateway can also be used to transport data
  to sensors for reprogramming, debugging and
  monitoring
• This exemplifies usefulness of being able to
  manage nodes directly via TCP/IP protocols

25

• HVAC Monitoring
• Explore feasibility of instrumenting a
  residential complex to improve the efficiency of
  its HVAC
• Temperature and vibration sensors of ESB are used
• IP based sensor accommodated into the Ethernet of
  the energy control room