Why Reliability

1
Sink-to-Sensors Reliability in Sensor
Networks Seung-Jong Park and Raghupathy Sivakumar
sjpark,siva_at_ece.gatech.edu GNAN Research
Group, Georgia Institute of Technology

• Why Reliability?
• Problem Environment
• Elements sink and sensors
• Sink sends queries and collects data from
  sensors.
• Sensor senses phenomenon and reports to sink.
• Communication Direction
• From sink to sensors in wireless sensor networks
• Target Problem
• Sink should perform reliable broadcast or
  multicast of data to sensors
• Size of information to transfer
• Single packet e.g. query for sensors or
  command for actuators.
• Multiple packets e.g. updated device driver and
  image data.

• Design Challenges and Choices
• Error Detection
• ACK scheme
• Although simple, it suffers from the ACK
  implosion problem.
• Negative ACK scheme
• NACK schemes are better for point-to-multipoint
  communication.
• Challenge
• How can NACK be used for single packet delivery,
  or more generically for cases where a sensor does
  not receive any packet?
• Error Recovery
• Local vs. non-Local Error Recovery Server scheme
• Local error recovery servers can recover losses
  faster
• than non-local recovery servers.
• Non-Local recovery scheme is not a scalable
  solution in
• large sensor networks
• Designated vs. Undesignated Error Recovery Server
• Because undesignated server schemes suffer from
• contention problems, designated server schemes
  are preferrable.
• Challenge
• How should local designated recovery servers be
  chosen

• Framework for Single Packet Delivery
• Single Packet Delivery with two frequencies
• Two frequencies R1 frequency for DATA
• R2 frequency for NACK
• Functionality of R2 Busy Tone Signal (BTS)
• BTS acts as a Negative ACK.
• Dynamic Core Construction
• The 1st packet constructs
• the core and non-core structure.
• Core nodes
• Located at 3 bands.
• Sparsely distributed
• Act as error recovery servers during multiple
  packet delivery.
• Non-core nodes
• Located at 1 and 2 bands.

Base Station
Sensor
Sensor
Sensor
Sink
Sensor
Sensor

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