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Scalable Data Aggregation for

Dynamic Events in Sensor NetworksKai-Wei Fan, Sha Liu, Prasun Sinha

Dept. of Computer Science and EngineeringThe Ohio State University

Sensys 2006

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Outline Introduction Dynamic Forwarding over tree on Directed Acy

clic Graph (ToD) One Dimensional Network Two Dimensional Network

Simulation Results Conclusion

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Introduction - Data

Aggregation Motivations

Communication cost is higher than computation cost

In-network processing reduces number/size of packets

Challenges Dynamic events Protocol must use low energy for long network

lifetime

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Introduction - Related Works Static Structure Dynamic Structure Structure-Free

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Data Aggregation ApproachesStatic Structure Routing on a pre-computed structure

Doesn’t need maintain overhead Suitable for unchanging traffic pattern

Inappropriate for dynamic event Without or Later data aggregation

a b

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Data Aggregation ApproachesDynamic Structure Create a structure dynamically Has optimal aggregation High control overhead for dynamic events

a bc

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Data Aggregation ApproachesStructure-Free (DAA, Infocom ’06)

Improve aggregation without any structure Data aware anycast to achieve spatial convergence Randomized waiting to improve temporal convergence

No guarantee of aggregation for allpackets

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Data aware anycast Based on anycasting at the MAC layer for determining the nex

t-hop node for each transmission Randomized Waiting

Each node generating a new packet to transmit, delays it by an interval chosen from 0 toτ

Sender

X

Sink

T=1

RTS(AID=1)

1

1

Sender

X

Sink

CTSSender

X

Sink

Pkt

Data Aggregation ApproachesStructure-Free (DAA, Infocom ’06)

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Introduction – Motivations and Goals Motivations

Propose a scalable structure-less protocol Structure-free: Local data aggregation Structured: further aggregation and Guarantee

early aggregation

Goals Low overhead of structure construction and

maintenance Suitable for dynamic event scenarios

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Dynamic Forwarding over ToD- Basic Idea

……

……………………

……………………

……

network

sink

sink

DAA

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Dynamic Forwarding over ToD- Basic Idea First phase: DAA

Packets are forwarded and aggregated to the selected node (F-aggregator)

Second phase: Dynamic forwarding Further aggregation (S-aggregator) In one dimensional networks In two dimensional networks

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Dynamic Forwarding over ToD- in one dimensional networks Assume a cell

a square with a side length is greater than the maximum diameter of

events

……

……………………

……………………

……

network

one row instance of the network

Cell

F-cluster S-cluster

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Dynamic Forwarding over ToD- F-Tree All nodes in F-clusters send their packets to their

cluster-heads, called F-aggregators Nodes in the F-cluster can be multiple hops away

from the F-aggregator. Each F-aggregator then creates a shortest path to

the sink

sink

F-clusters

F-cluster-head

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Dynamic Forwarding over ToD- S-Tree Each S-cluster also has a cluster head, S-

aggregator, for aggregating packets. Each S-aggregator create a shortest path

to the sink

sink

S-cluster

S-cluster-head

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Dynamic Forwarding over ToD- Further aggregation

sink

F-clusters

F-cluster-head

sink

S-cluster

S-cluster-head

a b

a b

f4

s4s3

sink

a b

f4

s4s3

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F1

Dynamic Forwarding over ToD- Three cases

sink

The Event occurs in one cell and a F-cluster

b

sink

F1

The Event occurs in two cells and a F-cluster

a b

sink

F1

S1

F2

The Event occurs in two cells and a S-cluster

b c

Using DAA to determine the event span one or two cells

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C1

A4 B3

B1 C2

A3

A1 A2 B2

B4 C3 C4

D3

D1 D2

D4 E3

E1 E2

E4 F3

F1 F2

F4

G1 G2 H1 H2 I1 I2

Dynamic Forwarding over ToD- in two dimensional networks

A B C

D

G H I

E F

S1 S2

S3 S4

G3 G4 H3 H4 I3 I4

F-Clusters Cells S-Clusters

An event can span at most four cells

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Dynamic Forwarding Rules For packets generated only in one F-cluster, their

packets can be aggregated at the F-aggregator An event triggers nodes in different F-clusters

In the same S-cluster: aggregate at the S-aggregator In the different two S-clusters

F-cluster

F-cluster head

S-cluster

S-cluster head

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Dynamic Forwarding Rules To guarantee the aggregation, the F-aggregator of

F-cluster X forwards the packet through two S-aggregators

To firstly select the S-aggregator that is closer to the sink

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Clustering and Aggregator Selection Assume that sensor nodes know their physical location Nodes in an F-cluster and S-cluster have to select an

aggregator and change the role periodically Elect themselves as cluster-head with probability based on

metrics such as the residual energy Use a hash function to hash the current time to a node within

that cluster To simplify the control overhead of the cluster head, F-

cluster-head also takes the role of S-cluster-head

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Simulation Results Simulator: ns2 2000m*1200m (35 X 58 grid network) A total of 1938 nodes TX Range: 50m Perfect aggregation

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Simulation Results

OPT

ToD

DAA

SPT

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Simulation Results

SourcesngContributiofNumber

onsTransmissiTotalofNumber

DAA

SPT

OPTToD

DAA

OPT

ToD

The event size is 400m in diameterNormalized number of transmission:

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Simulation Results

DAA

SPT

OPTToD

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Simulation Results

for difference cell sizes

Event Size: 200m, 400m, 600m in diameter

200m

400m

600m

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Conclusion Proposed a semi-structures approach

Structure-Free Aggregation Dynamic Forwarding on ToD for Scalability without overhead of structure computation and ma

intenance

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Thank you