CMPE 259

1
CMPE 259

• Sensor Networks
• Katia Obraczka
• Winter 2005
• MAC II

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Announcements

• Nacho will b talking about data aggregation on
  Mon., Feb. 28th.
• Exam Wed., March 2nd.
• Project status updates.
• E-mail 1 paragraph (plain text) describing
  progress so far and what remains to be done,
  plan, etc.
• Project submission also includes project report!

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Today

• Finish MAC.
• Start Storage, querying, and aggregation.

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FLAMA (contd from last class)
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TRAMA Limitations

• Complex election algorithm and data structure.
• Overhead due to explicit schedule propagation.
• Higher queuing delay.

Flow-aware, energy-efficient framework.
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Flow-aware Medium Access

• Avoid explicit schedule propagation.
• Take advantage of application.
• Simple election algorithm to suit systems with
  low memory and processing power (e.g., 4KB ROM in
  Motes).
• Incorporate time-synchronization, flow discovery,
  and neighbor discovery during random-access
  period.

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Flow Information

• Flow information characterizes application-specifi
  c traffic patterns.
• Flows can be unicast, multicast or broadcast.
• Characterized by source, destination, duration
  and rate.

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Example Data Gathering Application
C
Fc
D
Fd
B
Fb
A
Sink
Fe
E
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Flow Discovery Mechanism

• Combined with neighbor discovery during
  random-access period.
• Adapted based on the application.
• For data gathering application, flow discovery is
  essentially establishing the data forwarding tree.

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Example
Sink initiates neighbor discovery, flow
discovery, and time synchronization. Broadcasts
periodic SYNC packets. Potential children reply
with SYNC_REQ. Source reinforces with another
SYNC packet. Once associated with a parent,
nodes start sending periodic SYNC broadcasts.
B
SYNC
A
C
S
SYNC_REQ
Sink
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Election Process

• Weighted election to incorporate traffic
  adaptivity.
• Nodes are assigned weights based on their
  incoming and outgoing flows.
• Highest priority 2-hop node is elected as the
  transmitter.
• A node listens if any of its children has the
  highest 1-hop priority.
• Can switch to sleep mode if no transmission is
  started.

B
wc1
A
C
S
wc1
wa3
Sink ws0
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Simulation Results (16 nodes, 500x500 area,
CC1000 radio, grid topology, edge sink)
Queueing Delay
Delivery Ratio
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FLAMA Summary

• Simple algorithm that can be implemented on a
  sensor platform.
• Significant performance improvement by
  application awareness.

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Geographic Random Forwarding Zorzi e al.
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Approach busy tones

• Nodes assumed to have 2 radios.
• One used for data and another for signaling.
• Receiver uses busy tone to prevent collisions.
• Transmissions are broadcast.
• RTS/CTS.
• Any node can receive to RTS.
• CTSs subject to contention.

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Protocol operation transmitter

• Node has packet to send
• Listens to both frequencies for T.
• If either frequency busy, backoff.
• Otherwise, broadcast RTS with location of source
  and destination.
• Listens for CTS.
• If CTS received, sends data.
• If no CTS received after N trials, abort.
• If undistinguished signal, COLLISION.

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Transmitter (contd)

• After packet transmitted, wait for ACK.
• If ACK received, done and sleep.
• Otherwise, retransmit.

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Receiver

• Nodes wake up and listen.
• If no activity, go back to sleep.
• Otherwise, go to receive state and activate busy
  tone.
• When receiving RTS, node determines its priority
  as relay.
• Based on location info.
• First CTS slot, neighbors nearest to destination
  send CTS.
• Nodes listen for data.
• If data, only designated node receives all
  others go to sleep.
• Designated node is node that sent CTS
  (specified in data packet header).

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Receiver (contd)

• If CONTINUE, i.e., no node in closest region
  replied with CTS, nodes in 2nd. closest region
  will contend,
• If ABORT, transmitter reached maximum number of
  CTS slots.
• If COLLISION, more than one CTS was received.
• Colliding nodes execute collision resolution.

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Evaluation

• Analytical.
• Numerical results.
• Compared with STEM.
• Idle nodes sleep.
• Dual radio.
• Metrics
• Energy.
• Latency.
• Overhead?

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Results

• From paper