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1、Wireless Sensor Networks1PROTOCOL STACKApplication LayerApplication LayerTransport LayerTransport LayerNetwork LayerNetwork LayerLink LayerLink LayerPhysical LayerPhysical LayerPower Management PlaneMobility Management PlaneMobility Management PlaneTask Management PlaneWireless Sensor Networks2第五讲 T
2、ransport layerWireless Sensor Networks3TRANSPORT LAYER (PRIOR KNOWLEDGE) END TO END RELIABILITY CONGESTION CONTROL Congestion detection Fairness issues TCP (Transmission Control Protocol) for Data Traffic UDP (User Datagram Protocol) for Real Time TrafficWireless Sensor Networks4Transport LayerTrans
3、port LayerInternet, Internet, Satellite, etcSatellite, etcSinkSinkSinkSinkUserUserEnd-to-end communication End-to-end communication between a sensor node and between a sensor node and useruserEnd to end reliable event End to end reliable event transfer transfer Wireless Sensor Networks5ChallengesEnd
4、-to-End Measures Application-Dependent Operation Energy Consumption Biased Implementation Constrained Routing/Addressing Wireless Sensor Networks6End-to-End Measures TCP: End-to-end retransmission-based error control Window-based additive-increase multiplicative-decrease (AIMD) congestion control me
5、chanisms. End-to-end and point-to-point reliability and congestion control solutions Resource wastage in WSNsWireless Sensor Networks7The packet losses and congestion mitigation are performed through communication between a source and a destination without any involvement from the intermediate parti
6、es The transport control mechanisms reside only on the source and destination. Each flow is considered independently to provide a point-to -point communication solution. Wireless Sensor Networks8Collective information from a group of sensors is much more important than the individual information fro
7、m each sensor node. Conventional end-to- end, point-to-point transport layer techniques may lead to waste of scarce wireless sensor resources. Local measures for reliability and congestion control are usually exploited to improve the energy efficiency of the transport layer protocols Reliability of
8、the collective information from a group of sensors is controlled instead of the reliability of information from each individual sensor node. Wireless Sensor Networks9Related WorkWireless TCP variants are NOT suitable for sensor networks Different notion of end-to-end reliability Huge buffering requi
9、rements ACKing is energy draining BOTTOMLINE: Traditional end-to-end guaranteed reliability (TCP solutions) cannot be applied here. New Reliability Notion is required!New Reliability Notion is required!Wireless Sensor Networks10Congestion ControlACKfeedbackClosed-loop controlFeedback should be frequ
10、ent, but not too much otherwise there will be oscillations Can not control the behavior with a time granularity less than the feedback periodWireless Sensor Networks11TCP congestion controlcwnd grows exponentially (slow start), then linearly (congestion avoidance) with 1 more segment per RTT If loss
11、, divides threshold by 2 (multiplicative decrease) and restart with cwnd=1 packetTimeSequence NoCongestion window doubles every round-trip timepacket ackWireless Sensor Networks12ChallengesEnd-to-End Measures Application-Dependent Operation Energy Consumption Biased Implementation Constrained Routin
12、g/Addressing Wireless Sensor Networks13Application-Dependent Operation Deployed with a specific sensing application objective Monitoring application: Reliability Event detection applications: Timeliness Transport layer solutions - tailored to the application. The importance of these metrics can also
13、 vary according to the application area. The specific objective of WSNs influences the design requirements of the transport layer protocols. Wireless Sensor Networks14ChallengesEnd-to-End Measures Application-Dependent Operation Energy Consumption Biased Implementation Constrained Routing/Addressing
14、 Wireless Sensor Networks15Energy Consumption Scarce energy resources affect the design of transport layer solutions. Energy aware transport layer functionalities: reliability and energy power-end-to-end measures not be scalable for WSNs. Traded off between reliability and energy consumption- local
15、reliability measuresWireless Sensor Networks16ChallengesEnd-to-End Measures Application-Dependent Operation Energy Consumption Biased Implementation Constrained Routing/Addressing Wireless Sensor Networks17Biased Implementation Resource-constrained sensor nodes and resource-rich sink: Most of the fu
16、nctionalities are performed at the sink Minimum functionalities are required at the sensor nodes. Flow direction depending traffic: sensors-to-sink direction traffic require timely delivery with loss-tolerant operation Sink-to-sensors direction requires a high delivery ratio. Wireless Sensor Networks18ChallengesEnd-to-End Measures Application-Dependent Operation Energy Consumption Biased Implementation Constrained
