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Next Century Challenges: Scalable Coordination in

sensor NetworksMOBICOMM (1999)

Deborah Estrin, Ramesh Govindan, John Heidemann, Satish Kumar

Presented by

Mohammed Alam (shahed)

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OUTLINE

Introduction Challenges to Sensor Networks Localized Algorithms for Coordination Directed Diffusion Related Work Summary Discussion

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NETWORKED SENSORS

Sensor devices coordinating to achieve larger sensing task. EXAMPLE:

Tracking inventory Tracking motion of vehicles Temperature Noise level

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EXAMPLES of Sensors

29 Palms Fixed/Mobile ExperimentTracking vehicles with a UAV-delivered sensor network

TINY OS

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Design Challenges

Sheer number of devices Rule out traditional network device management Ratio of communicating nodes to users much

larger (1000 :1). Impossible to concentrate on specific sensors.

Power constraint Device failure common

Battery supply limited

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Design Challenges

Frequent change in position Sensors added Sensors moved Sensors removed

Out of power Damaged Unreachable

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Proposed Design Features

Data Centric Sensors do not need identity (no IP address) Application focus on data having attributes Communication primitive : “request” for data

Application Specific Intermediate nodes cache and aggregate

application specific data Forwarding requests (like routers)

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Proposed Solution

Localized Algorithm

Distributed algorithm

Sensors interact in restricted area

Collectively achieve global objective

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Localized algorithm

Achieved using clustering of sensors (Localized Clustering algorithm).

Advantages: Scalability Improved robustness Efficient resource utilization (battery power)

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Clustering in Sensor Networks

Child Sensor

Parent Sensor

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Goal of Localized Clustering algorithm

Elect cluster-head sensor such that each sensor has a cluster-head as parent.

no asymmetric connections

Cluster adapts to network dynamics and changing energy level of nodes

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Localized Clustering algorithm

Assume link level procedure on sensor

Adjusts Communication range by tweaking transmission power to minimum value for full network connectivity.

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Localized Clustering algorithm

Assume a multi-level cluster formation

Associate sensors at a level with radius

Radius: Number of physical hops sensor advertisement will travel

Sensors at higher level = larger radii.

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Localized Clustering algorithm

1 2 3 4

Level1

Level 0

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Localized Clustering algorithm

1 2 3 4

Level1

Level 0

Send advertisements

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Localized Clustering algorithm

1 2 3 4

Level1

Level 0

Send advertisements

Start promotion timers

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Localized Clustering algorithm

1

2

3

4

Level1

Level 0

promote

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Localized Clustering algorithm

1

2

3

4

Level1

Level 0

Notify potential children

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Localized Clustering algorithm

1

2

3

4

Level1

Level 0

Select parent

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Localized Clustering algorithm

1 2

3

4

Level1

Level 0

Demote (no child)

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Localized Clustering algorithm

1 2

3

4

Level1

Level 0

Select parent

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Localized Clustering algorithm

All sensors start at level 0. Sensors send periodic advertisement to

sensors within radius hops. Advertisements carry:

Hierarchy level Parent ID (if any) Remaining energy in sensor

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Localized Clustering algorithm

After sending advertisements: Sensors wait for wait time (proportional to radius). At end of wait time, if sensor does not have

parent Level 0 sensor starts promotion timer. Promotion timer inversely proportional to remaining

energy and number of level 0 advertisements received.

Smaller time out value for sensors in dense regions with more power.

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Localized Clustering algorithm

After promotion timer expires: Sensor promotes itself to level 1. Sends periodic advertisements at level 1 radius. Advertisement lists potential child sensors:

Sensors whose advertisement received in level 0.

The child sensors in lower level chooses the closest parent.

All sensors keep checking (parent, child) after wait time period.

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Localized Clustering algorithm

If battery power of parent sensor less than certain threshold compared to children Parent sensor drops a level down. Election takes place so that a new parent

selected with more power.

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Difficulty of Localized Algorithms

Should provide desired global behavior with indirect global knowledge Converting centralized algorithm to distributed. Difficulty in designing adaptability to different

environments and converge to global behavior over range

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Solutions to overcome disadvantage

Adaptive Fidelity Algorithm Quality of answer traded against battery life,

network bandwidth or number of active sensors

Develop Techniques for characterizing performance of Localized Algorithms sacrifice resource utilization, responsiveness

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Directed Diffusion

Set of abstractions that describe communication pattern in localized algorithms.

Sensors name data that it generates. Data contains attributes.

Other nodes express interests based on attributes.

Network nodes propagate interests.

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Directed Diffusion

Interest on data creates gradients that direct diffusion of data.

Gradients are data dissemination path from source to sink (requesting information) nodes.

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Example of Directed Diffusion

SINK

SOURCE

Gradient

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Related Work

Ad-hoc Networks Proactive vs. reactive routing protocols

Energy-efficiency issues

Distributed Robotics Robots cooperate to discover entire map

Internet Multicast and web caching Lightweight session

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Current Developments

Smartdust project: cubic millimeter sensors Sensors float in air like dust

WINS (wireless integrated wireless Sensors) WSN (Wireless Sensing Network) Odyssey Habitat monitoring

Great Duck Island

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Summary

Manage sensor networks using localized algorithm

Advantages of localized algorithm Robustness, Energy efficient, manage sheer

numbers Cluster approach for localization Directed Diffusion for communication among

sensors

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QUESTIONS

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DISCUSSION

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References

http://robotics.eecs.berkeley.edu/~pister/29Palms0103/ http://www.eecs.berkeley.edu/IPRO/Summary/

01abstracts/szewczyk.1.html http://nms.lcs.mit.edu/projects/leach/ http://citeseer.nj.nec.com/context/1822734/0 http://www.cens.ucla.edu/Estrin/index.shtml http://www.greatduckisland.net/images.php www.mdpi.net/sensors/papers/s20700286.pdf