ROUTING TECHNIQUES IN
WIRELESS SENSOR
NETWORKS: A SURVEY
Outline
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Background
Classification of Routing Protocols
Data Centric Protocols
 Flooding
and Gossiping
 SPIN
 Directed
Diffusion
 Rumor Routing
Background

Sensor nodes
 Small,
wireless, battery powered
 Energy, bandwidth constrained
 Data sensing, relaying, aggregating
 No global addressing scheme

Sink nodes
 More
powerful nodes
 Usually gateway to wired networks
 Data collecting and processing
Goal

So at network layer, it is highly desirable to find
methods for energy efficient route discovery and
relaying of data from the sensor nodes to the BS so
that the life time of the network is maximized.
Routing Protocols
Data-centric Protocols
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The ability to query a set of sensor nodes
Attribute-based naming
Data aggregation during relaying
For example:
 Flooding
& Gossiping
SPIN
 Directed Diffusion
 Rumor Routing

Flooding & Gossiping
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
In flooding, sensor broadcasts packets to all its
neighbors till dst reached or packets' ttl == 0
In gossiping, sensor sends packets to a randomly
selected neighbor which does the same
Flooding & Gossiping(cont.)
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Pros
 Simple
 No

routing, no state maintenance
Cons
 Implosion
 Overlap
Resource blindness
 Delay in Gossiping

SPIN – Sensor Protocols for
Information via Negotiation
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Metadata negotiation done before transmitting the
actual data.
3-way handshake: ADV, REQ, DATA
Event-driven
SPIN(cont.)
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Pros
 Solve
the classic problems
 Topological changes are localized

Cons
 No
guarantee on the delivery of data
Directed Diffusion
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Sink node floods named “interest” with larger
update interval
Sensor node sends back data via “gradients”
Sink node then sends the same “interest” with
smaller update interval
Query-driven
Directed Diffusion (cont)

Pros
 On
demand route setup
 Each node does aggregation and caching, thus good
energy efficiency and low delay

Cons
 Query-driven,
not a good choice for continuous data
delivery
 Extra overhead for data matching and queries
Rumor Routing
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A trade-off between Query & Event flooding
An agent, a long-lived packet, is generated when
events happen
The agent propagate the event to distant nodes
Rumor Routing (cont)
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Pros
 Avoid

query flooding
Cons
 Performs
well only when # of events is small
 Overhead to maintain agents and event-tables
Hierarchical Routing Protocols
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
When sensor density increases single tier networks
cause
Gateway overloading
Increased latency
Large energy consumption
Clustered Network allow coverage of large area of
interest and additional load without degrading the
performance
Hierarchical Routing Protocols
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Idea
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Partition the entire network into regions or clusters.
Select one or more nodes as the cluster head.
The routing is nodes -> cluster head A -> cluster head B ->
cluster head C -> nodes
The routing between cluster heads and the routing within a
cluster may follow different protocols (EGP-BGP and IGPOSPF).
Issues resolved: Energy wasted in collision, collision
avoidance, idle-listening
Achieves


Better scalability
Removes the load to less powerful nodes
The LEACH Protocol
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Low-Energy Adaptive Clustering Hierarchy.
Distributed cluster formation technique that enables
self-organization of large numbers of nodes.
LEACH - Setup
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Set up phase
Cluster Head (CH) selection (random + rotating)
 ADV
 Join REQ
 TDMA SCH prepared by CH (no collisions and reduced
energy consumption)

LEACH - Steady State
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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.
PEGASIS
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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.
Well, what was so bad in LEACH except for a bad
name...
PEGASIS - Concept
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Be Greedy!
Align with the one that has the max signal strength,
form a near-optimal chain.
Communicate with neighbors only.
But who takes care of communicating to BS?
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 (i mod
N node in round i out of N nodes shall transmit
to BS).
Passing the buck...

Token passing approach
The TEEN Protocol
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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.
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.
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).
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.
TEEN - Drawback
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
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-Adaptive
Periodic TEEN
This scheme practical implementation would have to
ensure that there are no collisions in the cluster.
GPSR: GREEDY PERIMETER
STATELESS ROUTING FOR WIRELESS
NETWORKS
Presentation Overview
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Introduction
Algorithm Key Ideas & Concepts
Examples
Evaluation Matrices & Results
Summary
GPSR Overview
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Routing Protocol that uses positions of routers and a
packet’s destination to make packet forwarding
decisions
GPSR keeps state only about the local topology (for
only a single hop)
The word “Stateless” is not meant literally but refers to
small, purely local state
GPSR scales better in per-router state than shortestpath and ad-hoc routing protocols
GPSR finds correct new route quickly under frequent
topology changes
Algorithm’s Key Ideas
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“The position of a packet’s destination and positions of
the candidate next hops are sufficient to make correct
forwarding decisions, without any other topological
information.”
“Routing protocol that rely on end-to-end state
concerning the path, face scaling challenge with
increasing number of routers & rate of change of
topology (mobility).”
“GPSR generates routing protocol traffic independent of
the length of the routes through the network, therefore
generates a constant, low volume protocol messages as
mobility increases,”
GPSR Modes
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Modes
 Nominal:
Greedy Forwarding
 Special : Perimeter Forwarding

Greedy Forwarding
 Uses
only information about router’s immediate
neighbors
 Forwarding node makes locally optimal greedy choice
of the packet’s next hop
Greedy Forwarding Example
Follows successive closer geographic hops, until the
destination is reached
Perimeter Forwarding
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Used in the region where Greedy forwarding fails.
There are topologies in which the only route to a
destination requires a packet move temporarily
farther in geometric distance from the destination
Special mechanism (right hand rule) is used in such
special situation
Perimeter Forwarding Example
When Greedy Forwarding Fails.
x is a local maximum in geographic proximity to D
w and y are farther from D
Right Hand Rule: x
receives a packet from
y, and forwards it to its
first neighbor
counterclockwise about
itself , z
Perimeter Forwarding Example
D is the destination; x is the node where the packet enters perimeter mode;
forwarding hops are solid arrows; the line xD is dashed.
• GPSR forwards packets along the face intersected by the line xD
• x forwards the packet to the first edge counterclockwise about x
form the line xD, follows right hand rule thereafter
Network Graphs
Full Graph
Planar Graph
Greedy Forwarding
Perimeter Forwarding
Planarized Graphs
The RNG graph.
For edge(u; v) to be
included, the shaded lune
must contain no witness w.
The GG graph.
For edge(u; v) to be
included, the shaded circle
must contain no witness w.
GPSR Operation
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GPSR combines greedy forwarding on full network
graph and perimeter forwarding in planarized
network graphs
All nodes maintain neighbor table, which stores the
address and location of their single-hop radio
neighbors
The table provides all states required for
forwarding decisions
GPSR Operation
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All packets are marked initially as greedy mode
Upon receiving a greedy-mode packet, a node
searches its neighbor table geographically closest
to the packet’s destination.
If the neighbor is closer to the destination, it
forwards the packet to the neighbor.
If no neighbor is closer, the packet is marked into
perimeter mode.
GPSR Operation
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In perimeter mode, the packet is forwarded using a
simple planner graph
The packet is forwarded to progressively closer faces
of the planner graph using the right hand rule
In perimeter node, the GPSR records the location where
greedy failed, and the first edge a packet crosses on a
new face
When the destination is not reachable, the packet will
tour unsuccessfully around the entire face as no
intersection with xD is detected
Upon traversing on the face second time, the repetition
is detected to correctly drop the packet
Algorithm Evaluation Matrices
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Packet delivery success rate
 Fraction
of applications’ packets delivered successfully
by the routing algorithm

Routing protocol overhead
 Per-node
state: storage required at each node
 Protocol message cost: number of protocol packets sent
by the routing algorithm

Optimality of path lengths taken by data packets
Packet Delivery Success Rate
GPSR delivers a slightly
greater fraction of
packets successfully than
DSR
Pause time is the time
duration for which all nodes
hold the same positions at
waypoints.
The mobility model used is
the random way point
model which generates
waypoints at random.
GPSR with varying beacon intervals, B, compared with Dynamic Source Routing
(DSR). 50 nodes
Routing Protocol Overhead
GPSR offers
greater savings
in routing
protocol
overhead
Total routing protocol packets sent network-wide during the simulation for GP R with varying
beacon intervals, B, compared with DSR. 50 nodes.
Packet Delivery Success Rate
GPSR delivers
97% of its
packets along
optimal-length
paths vs. 84.9%
for DSR
Packet Delivery Success Ra t e . F o r G P S R with B = 1.5 compared with DSR.
50, 112, a n d 200 node s .
Routing Protocol Overhead
GPSR generates
drastically less
routing protocol
traffic w.r.t. to DSR
Total routing protocol packets sent network-wide during the simulation for GPSR with B = 1.5
compared with DSR. y axis log-scaled. 50, 112, and 200 nodes.
Summary
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GPSR routing algorithm uses geography to achieve small
per-node route state, small routing protocol message
complexity, and extremely robust packet delivery
GPSR generates routing protocol traffic independent of the
length of the routes through the network, therefore
generates a constant, low volume protocol messages as
mobility increases
GPSR performs better than DSR. GPSR keeps states
proportional to no. of neighbors; DSR keeps sates
proportional to product of no of routes learned and route
length in hops.
Besides Hierarchy and Caching, Geography is leverages for
scaling routing
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Thank you