Protocols for Wireless
Sensor Networks
1
Outline


Introduction
Flat Routing Protocols



Hierarchical Routing Protocols





Directed Diffusion
SPIN
LEACH
PEGASIS
TEEN
Topic for Discussion
References
2
Introduction to WSNs

A sensor network is a computer network of
many, spacially distributed devices using
sensors to monitor conditions at different
locations.

Involve three areas: sensing,
communications, and computation.
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Introduction to WSNs

Sensor nodes scattered in a sensor field


Each nodes has the capabilities to collect data and route data
back to the sink (Base Station).
Protocols and algorithms with self-organization capabilities.
4
Introduction - WSNs Topology

Issues related to topology maintenance and change in
three phases:

Pre-deployment and deployment phase:


Post-deployment phase:


Sensor nodes can be either thrown in mass or placed one by one in
the sensor field.
Topology changes are due to change nodes' position, reachability,
available energy, malfunctioning, and task details.
Re-deployment of additional nodes phase:

Additional sensor nodes can be redeployed at any time to replace
malfunctioning nodes or due to changes in task dynamics.
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Types of Routing Protocol for WSN

Single-hop Networks
 The
network consists of n nodes, and packets are
transmitted from sources to destinations directly.

Multi-hop Networks
 The
final destination of a packet might not be reached
directly and the other nodes can be used to route the
packet to the final destination.
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Flat Routing Protocols

Flat Networks

Every incoming packet is sent out on every
outgoing line except the one it arrived on.
 Vast numbers of duplicate packets are
generated.
 Routing Protocols: Directed Diffusion, SPIN.
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The Directed Diffusion Protocol

Directed Diffusion consists of several
elements:
 Interests
 Data
messages
 Gradients
 Reinforcements
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Directed Diffusion - Interest & Data

Interest






type = wheeled vehicle
interval = 1 s
rect = [-100, 200, 200, 400]
timestamp = 01:20:40
// hh:mm:ss
expiresAt = 01:30:40
Data





type = wheeled vehicle
instance = trunk
location = [125, 220]
intensity = 0.6
confidence = 0.85
 timestamp = 01:20:40
// type of vehicle seen
// instance of this type
// node location
// signal amplitude measure
// confidence in the match
// local event generation time
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Directed Diffusion - Interest
Propagation

The sink periodically
broadcasts an interest
message to each of its
neighbors.

Every node maintains
an interest cache.
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Directed Diffusion - Gradient
Establishment

That every pair of
neighboring nodes
establishes a gradient
toward each other.

This technique can
enable fast recovery
from failed paths or
reinforcement of
empirically better paths.
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Directed Diffusion - Data
Propagation

A sensor node that detects a target, it
computes the highest requested event rate
among all its outgoing gradients.

To resend a received data message, a
node needs to examine the matching
interest entry's gradient list.
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Directed Diffusion - Reinforcement

The node might choose
that neighbor from
whom it first received
the latest event
matching the interest to
reinforce.

It is very reactive to
changes in path quality.
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The SPIN Protocol

Sensor Protocols for Information via
Negotiation.

Start with a source node sending its data
to all of its neighbors.
14
SPIN - Flooding deficiencies

Implosion & Overlap
(a)
A
B
r
(a)
C
(a)
(a)
D
Implosion Problem
q
s
A
B
(q, r)
C
(r, s)
Overlap Problem
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SPIN-1 - three types of messages

ADV
 When
a SPIN node has data to share, it can advertise
an ADV message containing meta-data.

REQ
 A SPIN
node sends an REQ message when it wishes
to receive some actual data.

DATA
 DATA messages
contain actual sensor data with a
meta-data header.
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The SPIN-1 Protocol

Steps
C
DATA
REQ
ADV
ADV
D
E
B
DATA
ADV
REQ
A
ADV
REQ
ADV
DATA
F
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The SPIN-2 Protocol

When energy is plentiful, SPIN-2 nodes
communicate using the same 3-stage
protocol as SPIN-1 nodes.

When a SPIN-2 node observes that its
energy is approaching a low-energy
threshold, it adapts by reducing its
participation in the protocol.
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Hierarchical Routing Protocols

Hierarchical Networks
 The
main aim of hierarchical routing is to
efficiently maintain the energy consumption of
sensor nodes.
 Performing data aggregation and fusion in
order to decrease the number of transmitted
messages to the sink.
 Routing Protocols: LEACH, PEGASIS, TEEN.
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The LEACH Protocol

Low-Energy Adaptive Clustering Hierarchy.

Distributed cluster formation technique
that enables self-organization of large
numbers of nodes.
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LEACH - Cluster

Algorithms for adapting clusters and rotating cluster
head positions to evenly distribute the energy load
among all the nodes.

The nodes organize themselves into local clusters, with
one node acting as the cluster head.

The cluster head performs signal processing functions
on the data, and transmits data to the remote BS.
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LEACH - Set-up phase

Cluster Head
 Each
cluster head node broadcasts an advertisement
message (ADV) let all the other nodes that they have
chosen this role for the current round.

Non-Cluster Head
 They
transmits a join-request message (Join-REQ)
back to the chosen cluster head.
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LEACH - Set-up phase

The cluster head node sets up a TDMA schedule
and transmits this schedule to the nodes in the
cluster.

Ensures that there are no collisions among data
messages.

Allows the radio components to be turned off at
all times except during their transmit time.
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LEACH - Steady-state phase

Broken into frames, where nodes send
their data to the cluster head at most once
per frame during their allocated
transmission slot.

Once the cluster head receives all the data,
it performs data aggregation.
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LEACH - Time line

Time line showing LEACH operation
ADV Join-REQ
SCH
Slot for NCH2
Set-up phase
NCH1 NCH2
…
…
…
NCHm-1 NCHm
Frame
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The PEGASIS Protocol

Power-Efficient GAthering in Sensor
Information Systems.

The key idea in PEGASIS is to form a
chain among the sensor nodes so that
each node will receive from and
transmit to a close neighbor.
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PEGASIS - Chain

The nodes will be organized to form a
chain, which can either be accomplished
by the sensor nodes themselves using a
greedy algorithm starting from some node.

When a node dies, the chain is
reconstructed in the same manner to
bypass the dead node.
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PEGASIS - Leader

The main idea in PEGASIS is for each node to
receive from and transmit to close neighbors
and take turns being the leader for transmission
to the BS.

Nodes take turns transmitting to the BS, and we
will use node number i mod N (N represents the
number of nodes) to transmit to the BS in round i.
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PEGASIS - Token

Token passing approach
N0
N1
N2
N3
N4
BS
Token
Data
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The TEEN Protocol

Threshold sensitive Energy Efficient sensor Network
protocol.

Proactive Protocols (LEACH)


The nodes in this network periodically switch on their sensors
and transmitters, sense the environment and transmit the data of
interest.
Reactive Protocols (TEEN)

The nodes react immediately to sudden and drastic changes in
the value of a sensed attribute.
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TEEN - Functioning

At every cluster change time, the cluster-head
broadcasts to its members
 Hard Threshold (HT)
 This is a threshold value for the sensed attribute.
 It is the absolute value of the attribute beyond which, the
node sensing this value must switch on its transmitter and
report to its cluster head.
 Soft Threshold (ST)
 This is a small change in the value of the sensed attribute
which triggers the node to switch on its transmitter and
transmit.
31
TEEN - Hard Threshold

The first time a parameter from the
attribute set reaches its hard threshold
value, the node switches on its transmitter
and sends the sensed data.

The sensed value is stored in an internal
variable in the node, called the sensed
value (SV).
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TEEN - Soft Threshold

The nodes will next transmit data in the
current cluster period, only when both the
following conditions are true:
 The
current value of the sensed attribute is
greater than the hard threshold.
 The current value of the sensed attribute
differs from SV by an amount equal to or
greater than the soft threshold.
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TEEN - Drawback

If the thresholds are not reached, the user
will not get any data from the network at all
and will not come to know even if all the
nodes die.

This scheme practical implementation
would have to ensure that there are no
collisions in the cluster.
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References

I.F. Akyildiz, W. Su*, Y. Sankarasubramaniam, and E. Cayirci,


K. Akkaya, M. Younis,


"An Application-Specific Protocol Architecture for Wireless Microsensor Networks".
S. Lindsey and C. Raghavendra,


"Adaptive Protocols for Information Dissemination in Wireless Sensor Networks".
W. Heinzelman, A. Chandrakasan, and H. Balakrishnan,


"Directed Diffusion: A Scalable and Robust Communication Paradigm for Sensor Networks".
W. Heinzelman, J. Kulik, and H. Balakrishnan,


"Routing Techniques in Wireless Sensor Networks".
C. Intanagonwiwat, R. Govindan, and D. Estrin,


"A Survey on Routing Protocols for Wireless Sensor Networks".
J.N. Al-Karaki, A.E. Kamal,


"Wireless sensor networks: a survey".
"PEGASIS: Power-Efficient Gathering in Sensor Information Systems".
A. Manjeshwar and D. Agrawal,

"TEEN: A Routing Protocol for Enhanced Efficiency in Wireless Sensor Networks".
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