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Distributed Hop-by-Hop Rate Adjustment for Congestion Control in Sensor Networks Presented by: Manmohan Voniyadka Sapna Dixit Vipul Bhasin Vishal Kumar Singh
Agenda • Problem description • Solution requirements • Algorithm description • Congestion pricing scheme • Rate adjustment using price of congestion • Protocol details • Open Issues • Schedules and Work Distribution
Problem Description • Rate Adjustment to avoid congestion • Calculation of congestion pricing via a distributed mechanism
Solution Requirements • Develop a congestion pricing scheme • Develop a relationship between rate and the congestion pricing. • Modify CODA Protocol to incorporate these changes
Congestion Pricing Scheme • Factors for pricing • MAC utilization. • Congestion Price at Downstream Nodes. • Calculate a cumulative congestion pricing factor. • Calculate pricing factor in a distributed manner. • Weigh the pricing on congestion nodes appropriately.
Congestion Pricing Calculation • Cumulative Congestion Pricing: • wi– relative weight of downstream node, i • wi= • N is the Nth node from the congested node • cpicongestion pricing at the ith node • pj is a marking function (As given in )
Rate Adjustment Using Congestion Pricing • Use an AIMD Strategy:
Protocol Details • Conditions for Backpressure Origination • Send backpressure when threshold is exceeded as done in CODA • Threshold based on channel sampling • Header Format Changes • Extra field for price of congestion value in backpressure messages • End-to-End Loop Control
Open Issues • Relative weight in Congestion pricing is only based on congestion price at downstream nodes, Need to add Transmission rate at ith node as factor in weight. • Whether to use price of congestion for end to end loop control for controlling the source rate during persistent congestion. • What happens with Asymmetric links ?
Changes to existing CODA • Changes in Suppression Message generation. • Threshold based on MAC Utilization / channel Sampling. • Calculate and Send Congestion Price. • Changes in ReceiveBackPressure Message -> AdjustSourceRate.
Glossary • CPj = P (j) * MAC Utilization (j). CPj is the congestion price for using node j per unit time. • P(j) is the marking function at node j and determines the fraction of flow to be marked. • MAC Util is the fraction of time node j spends in receiving and re-transmitting to next hop. • P (j) = P (j) = (y - tj) / y • y is sum of MAC utilization time by all flows at node j. • tj is a parameter for controlling MAC time utilization. • P (j) indicates fraction of flow exceeding the threshold parameter. If link quality is bad , We make tj << 1 for lower MAC time utilization.
References  Chieh-Yih Wan, Shane B. Eisenman and Andrew T. Campbell, “CODA: Congestion Detection and Avoidance in Sensor Networks”, ACM SenSys 2003, November 2003. Y. Yi and S. Shakkottai. Hop-by-hop Congestion Control over a Wireless Multi-hop Network,“ IEEE INFOCOM, 2004.