Protocols for wireless sensor networks

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Protocols for Wireless
Sensor Networks
By: Debabrata Singh
Dept. of CSIT,ITER
SOA University, Bhubaneswar
Mail: debabratasingh@soa.ac.in

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Outline
 Introduction
 Flat Routing Protocols
 Directed Diffusion
 SPIN(Sensor Protocol for Information via Negotiation. )
 Hierarchical Routing Protocols
 LEACH(Low-energy adaptive clustering hierarchy)
 PEGASIS(Power Efficient Gathering in Sensor Information
Systems )
 TEEN(Threshold-sensitive energy efficient sensor network
(TEEN))
 Topic for Discussion
 References

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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.

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Introduction - WSNs Topology
 Issues related to topology maintenance and change in
three phases:
 Pre-deployment and deployment phase:
 Sensor nodes can be either thrown in mass or placed one by one in
the sensor field.
 Post-deployment phase:
 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
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.

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SPIN - Flooding deficiencies
 Implosion & Overlap
(a)
(a)
(a)
A
B C
D
(a)
(r, s)(q, r)
A B
C
q s
r
Implosion Problem 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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ADVREQ
The SPIN-1 Protocol
 Steps
B A
C
D
E
F
DATA
ADV
ADV
ADV
ADVREQ
REQ
DATA
DATA

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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
NCH1 NCH2 … … … NCHm-1 NCHm
Slot for NCH2
Frame
ADV Join-REQ SCH
Set-up phase

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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.

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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,
 "Wireless sensor networks: a survey".
 K. Akkaya, M. Younis,
 "A Survey on Routing Protocols for Wireless Sensor Networks".
 J.N. Al-Karaki, A.E. Kamal,
 "Routing Techniques in Wireless Sensor Networks".
 C. Intanagonwiwat, R. Govindan, and D. Estrin,
 "Directed Diffusion: A Scalable and Robust Communication Paradigm for Sensor Networks".
 W. Heinzelman, J. Kulik, and H. Balakrishnan,
 "Adaptive Protocols for Information Dissemination in Wireless Sensor Networks".
 W. Heinzelman, A. Chandrakasan, and H. Balakrishnan,
 "An Application-Specific Protocol Architecture for Wireless Microsensor Networks".
 S. Lindsey and C. Raghavendra,
 "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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