Esrt: Event-to-Sink Reliable Transport in Wireless Sensor Networks[Sankarasubramaniam et al, Acm mobiHoc 2003]

ESRT: Event-to-Sink Reliable Transport in Wireless Sensor Networks[Sankarasubramaniam et. al, ACM MobiHoc 2003]

• Prepared by A. ABOUZEID

Event Detection in a WSN

Motivation

• A sink is only interested in the collective information from a number of source nodes and not in individual sensor reports

• Event-to-sink communication

• Different from traditional notion of end-to-end communication

• Energy-efficient

• Congestion resolution

Problem Statement

• To configure the reporting rate f of source nodes so as to achieve the required event detection reliability R at the sink with minimum resource utilization

• Also resolve congestion

Typical Behavior at a Sink

Five characteristic regions

Congestion Detection

• Congestion status is required at the sink to determine the network state

• Based on expectation of buffer overflow at sensor nodes

• During a single interval, f and n do not change much

• If pending congestion is detected CN bit is set in event reports

ESRT Actions

ESRT State Diagram

Stability of ESRT

• ESRT converges to OOR from any of four initial states {(NC,LR), (NC,HR), (C,HR), (C,LR)}

• From (NC,HR), ESRT stays in the state until converges to OOR

• Convergence time depends on ε – smaller ε causes longer convergence time

Simulation Setup

• Ns-2 simulator

• 200 sensor nodes

• 100m x 100m area

• 40m transmission range

• 30 byte packets

• 65 packets IFQ

• 10 sec decision interval (τ)

From (NC,LR)

From (NC,HR)

(C,HR) to (NC,HR) then OOR

(C,LR) to (NC,LR) then OOR

Power savings from (NC,HR)

Conclusion

• ESRT provides a reliable event-to-sink communication

• Self-configuration
• Energy awareness
• Uses minimum energy while achieving required reliability
• Congestion control
• Collective identification
• Individual sensor ID is not necessary
• Biased implementation
• Almost entirely in sink

Questions

• Definition of reliability as number of received packets?

• Is ESRT congestion detection accurate and reliable?

• ESRT action heavily depends on the congestion state
• What if the congestion reports are inconsistent due to partial congestion or underlying path oscillation?
• What is the effect of inaccurate congestion state detection on ESRT?

• Is it reasonable assumption that a sink is capable of broadcasting to all the source nodes ?

• what if R is higher than the peak point?

Questions continued

• Out of band?
• If in-band, how to deal with congestion?

• What if the density of source nodes is too low to meet the required reliability with fast reporting?

• In other words,