Reliable, Robust Data Collection in Sensor Networks

Murali Rangan

Russell Sears

Fall 2005 – Sensornet

Motivation

Data collection apps like habitat monitoring All of the logged data is valuable Real time / in order delivery not important In-network aggregation not required

Current data collection mechanisms Lose data during temporary network partitions Or, store all data in each node

Our goal Reliable, robust scheme to collect ALL the data in

a steady stream, without in order guarantees

Our approach

Reliability Link level, hop-by-hop acknowledgements Introduce redundancy with k replicas of data Replicas ensure their data reaches the base

station, or pass responsibility to a parent. Take advantage of broadcast medium Take advantage of existing routing algorithms

(like MintRoute) for parent selection Keep basic mechanism simple, add

optimization on top

Algorithm overview

Node with new data Broadcasts request for k volunteers (for replicas) Parent(s) agree to volunteer Broadcasts data to volunteer(s) Volunteer(s) broadcast hop ACK (HACK) Once k volunteers are found, deletes data

Volunteer transfers responsibility upstream Repeats above process, seeking 1 volunteer Once responsibility is transferred, deletes data

Can volunteer for same data again!

Status and Future Work

Basic algorithm details are fleshed out Implement and simulate using TOSSIM

Work in progress! Address the following challenges

How many replicas? Depends upon network density, reliability

Base station broadcasts ACK to remove replicas of collected data Use bloom filters to summarize? Limit broadcast to ‘interested’ nodes?

How to bound k replicas? Eavesdropping?

How do we deal with fan-in near the base station? Few parents / replicas share paths

Prerequisites

Use any routing protocol that Assigns ‘parent(s)’ to each mote Adapts to changes in network topology

Reliable link level delivery Make use of broadcast medium Transfer data from a child node to its parents ACK’s transfer responsibility for a piece of data. (Dropped ACK’s

lead to more replicas) Broadcast ACK from base station

Guarantees replicas are eventually deleted Efficient, reliable broadcast?

Bloom filters? Reverse path routing + eavesdropping?

Sketch of algorithm

Inserting data into the network Broadcast request for k volunteers Broadcast data, volunteers (parents) ACK Once k volunteers are found, node deletes data.

Volunteers request enough volunteers to create k replicas in network.

(Usually, just create 1 volunteer) Pass ACK’s to children after creating > 1 replica.

Challenges How many replicas? What about fan-in?

Replicas share < k parents Shared paths?

How can we optimize propagation?