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Transport protocols in Wireless Sensor Networks

Transport protocols in Wireless Sensor Networks. Congduc PHAM University of Pau LIUPPA laboratory. Transport layer for WSN/WMSN. Reliability/loss recovery Congestion control Congestion detection Fairness issues Higher semantic than packet level Multipoint communication

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Transport protocols in Wireless Sensor Networks

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  1. Transport protocols in Wireless Sensor Networks Congduc PHAM University of Pau LIUPPA laboratory

  2. 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

  3. feedback Congestion 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 Closed-loop control

  4. Congestion window doubles every round-trip time packet ack Sequence No Time TCP congestion control 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 From Computer Networks, A. Tanenbaum

  5. 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: hop-by-hop CC more efficient than E2E? • WSN are collaborative in nature. Fairness issues less important?

  6. Reference architecture

  7. 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

  8. 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

  9. 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

  10. 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

  11. Proposals for WSNs • ESRT • CODA • PSFQ • RMST • HDA • GARUDA • SenTCP • STCP See the reference section for complete references of the papers

  12. 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

  13. 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

  14. Related projects • SensEye, UMass • http://sensors.cs.umass.edu/projects/senseye/ • Cyclops, UCLA • Panoptes, Portland State University • VSAM team at Carnegie Mellon Univ.

  15. Test-case in TCAP Grid-based localization? Lower priority, backup sensor?

  16. 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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