Congestion Control and Reliable Transport By salah shahin

1. Congestion Control and Reliable TransportBy salah shahin In Sensor Networks

2. Congestion Control • Why we need special congestion control? Sensor networks operate under an idle or light load and then suddenly become active in response to a detected or monitored event. Depending on the application (tracking, habitat monitoring, earthquakes) this can result in the generation of large, sudden, and correlated impulses of data (50 event/s or more) that must be delivered to a small number of sinks without significantly disrupting the performance of the sensing application. Less congestion →more reliability • The Suggested Solution : Energy efficient congestion control scheme for sensor networks called CODA (Congestion Detection and Avoidance) that comprises three mechanisms.

3. CODA Mechanisms (1) Receiver-based Congestion Detection. (2) Open-loop hop-by-hop Backpressure. (3) Closed-loop Multi-source regulation.

4. CODA Mechanisms • 1) Receiver-based Congestion Detection Instead of Listening to the channel to measure local loading which incurs high energy costs if performed all the time, CODA activate local channel monitoring at the appropriate time to minimize cost while forming an accurate estimate. • Appropriate time: only when the node receives a backpressure message. Once congestion is detected, nodes signal their upstream neighbors via a backpressure mechanism.

5. Congestion detection techniques • A nearly overflowing queue. • A measured channel load higher than a fraction of the optimum utilization. This provides a probabilistic indication of congestion by observing how closely the channel load approaches the upper bound. • Report Rate: When a sink consistently receives a less than desired reporting rate, it can be inferred that packets are being dropped along the path most probably due to congestion. This technique is used to measure fidelity too. • Fidelity= received events sent events

6. Continue: CODA Mechanisms 2)Open-loop hop-by-hop Backpressure. • If the sink detect congestion, it will broadcasts backpressure signals. Backpressure signals are propagated upstream toward the source but it will not reach it( open loop ). • Node that receive backpressure signal may throttle sending rates or drop packets only if congestion detected at this node. if not, this node will forward the backpressure signal upstream. • When an upstream node (toward the source) receives a backpressure message it decides whether or not to further propagate the backpressure upstream, based on its own local network conditions. • Open loop: backpressure message will not reach the source, it will stop at the node where the congestion is.

7. Continue: CODA Mechanisms 3) Closed-loop Multi-source Regulation • CODA only regulates the sources associated with a data event that have contributed to congestion or are impeded by hotspots between the sources and sink . • When the source event rate is less than some fraction(70%) of the maximum theoretical throughput of the channel, the source regulates itself by setting a regulate bit in the event packets which forwards toward the sink. • Hotspots: nodes that congested before. • Regulate: slow sending rate. • Closed loop: source →sink , sink →source .

8. Computing Source Event Rate • Constant, slow time-scale feedback (e.g., ACK) from the sink to maintain source rate. The reception of ACKs at sources serve as a self-clocking mechanism allowing sources to maintain their current event rates. • In contrast, failure to receive 70% of ACKs forces a source to reduce its own rate.

9. Simulation results • The source rates are: Src-1: 8pps(packets per second) Src-2: 4pps, Src-3: 7pps • Priority: Src-2, Src-3, Src-1

10. Simulation results

11. Simulation results Ratio: between the total number of packets dropped in the sensor network and total number of packets received

12. Simulation results • Simulation results indicated that CODA can improve the performance of directed diffusion by significantly reducing the average energy tax with minimal fidelity penalty to the sensing application. • Coda disadvantage: continue slow the rate of events for a long time→ less reliability.

13. ESRT: Event to Sink Reliable Transport Reliability: number of received packets

14. ESRT: Definition • ESRT is a novel transport solution that seeks to achieve reliable event detection with minimum energy cost and congestion resolution. It has been tailored to match the unique requirements of WSN. • ESRT is the First time consideration(2003). • ESRT has been designed for use in typical WSN applications involving event detection and signal estimation/tracking, and not for guaranteed end-to-end data delivery services.

15. ESRT: Mechanisms

17. ESRT: Results • Hence, a good choice of ε is one that balances the tolerance and convergence requirements. • ESRT has been designed for use in typical WSN applications involving event detection and signal estimation/tracking, and not for guaranteed end-to-end data delivery services