Transport protocols in
Wireless Sensor Networks
Congduc PHAM
University of Pau
LIUPPA laboratory
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Transport layer for
WSN/WMSN
Reliability/loss recovery
Congestion control
Congestion detection
Fairness issues
Higher semantic than packet level
Multipoint communication
Data aggregation, data dissemination
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Congestion Control

feedback
Closed-loop control
Feedback should be frequent, but not too much otherwise there will be oscillations
Can not control the behavior with a time granularity less than the feedback period
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TCP congestion control
From Computer Networks, A. Tanenbaum
Sequence No
Congestion window
doubles every round-trip
time
packet
ack
Time
cwnd grows exponentially (slow start), then linearly (congestion
avoidance) with 1 more segment per RTT
If loss, divides threshold by 2 (multiplicative decrease) and restart
with cwnd=1 packet
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WSN vs Internet
Small fraction of time dealing with
impulses, but data of greatest importance!
As in wireless transmission, difficult to
distinguish congestions from node failures
or bad channel quality
Sensors have limited resources
Simplicity in congestion detection and control
algorithms
Great interest of in-network processing: hopby-hop CC more efficient than E2E?
WSN are collaborative in nature. Fairness
issues less important?
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Reference architecture
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CC scenario in WSN
Densely deployed sensors
Persistent hotspots
Congestion occur near the sources
Sparsely deployed sensors, low rate
Transient hotspots
Congestion anywhere but likely far from the
sources, towards the sink
Sparsely deployed sensors, high rate
Both persistent and transient hotspots
Hotspot distributed throughout the network
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Some ideas for CC in WSN
Congestion detection
Monitor buffer/queue size
Monitor channel busy time, estimate channel’s load
Monitor the inter-packet arrival time (data, ctrl)
Congestion notification
Explicit congestion notification in packet header,
then broadcast (but then energy-consuming!)
Congestion control
Dynamic reporting rate depending on congestion
level
In-network data reduction techniques (agressive
aggregation) on congestion
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TCP or UDP?
TCP
Connection-oriented, 3-way handshake
Assumes segment losses results from
congestion
E2E reliability, congestion mechanism
Fairness as a function of RTT
UDP
No flow control nor congestion control
No reliability
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TCP or specialized approach?
TCP with appropriate modifications is
better than UDP is standardized
protocols are to be used.
Specialized approaches
allow for a specific preference between
reliability and congestion control
Application awareness is also possible
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Proposals for WSNs
ESRT
CODA
PSFQ
RMST
HDA
GARUDA
SenTCP
STCP
See the reference section for
complete references of the
papers
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Which CC for WMSN? (1)
WSN: scalar data
Wireless Multimedia Sensor
Networks add video, audio for
Enlarging the view
• Field of View of single camera is limited
• Multiples camera overcome occlusion effects
Enhancing the view
• Can help disambiguate cluttered situations
Enabling multi-resolution views
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Which CC for WMSN? (2)
Reliability should be enforced at the
packet level
Some packets are more important than
others in most of video coding schemes
Collaborative in-network processing
Reduce amap the amount of (redundant)
raw streams to the sink
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Related projects
SensEye, UMass
 http://sensors.cs.umass.edu/projects/senseye/
Cyclops, UCLA
Panoptes, Portland State University
VSAM team at Carnegie Mellon Univ.
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Test-case in TCAP
Grid-based localization?
Lower priority,
backup sensor?
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Design issues & directions
Cross-layering
Use low-level information
Collaborative in-network processing
Distributed algorithms
Router-assisted, node-assisted, ad-hoc
Simple congestion detection
mechanism
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