1. National Conference on Current Trends in Computer Science and Engineering - CSECONF2012
Network Structure Routing Protocols in WSN
Jain Pratik P1, Manjunath CR2 , DrNagaraj GS3
1 nd
MTech 2 Sem, SET, JAIN University, pratikjain1690@gmail.com
2
Asst Prof, Dept of CSE, SET, JAIN University, manjucr123@gmail.com
3
professor, Dept of CSE, RVCE
ABSTRACT- Routing protocols are in charge of play different roles in the network. In location-
discovering and maintaining the routes in the based routing, sensor nodes' positions are exploited
network. This paper presents a review of the main to route data in the network [2]. A routing protocol
routing protocols proposed for Network Structure in is considered adaptive if certain system parameters
WSN. Based on the study, they are classified into
can be controlled in order to adapt to the current
three categories: SPIN & Directed Diffusion in Flat-
based, LEACH, PEGASIS & SOP in Hierarchical- network conditions and available energy levels.
based, SPAN & GOFAR in Location-based, which Another class of routing protocols is called the
underlying Network Structure. cooperative routing protocols. In cooperative
routing, nodes send data to a central node where
Keywords- Wireless Sensor Network, Routing data can be aggregated and may be subject to
Protocols: Flat-based, Hierarchical-based, Location- further processing, hence reducing route cost in
based. terms of energy use [2].
I. INTRODUCTION II. Flat-based Routing Protocols
Wireless Sensor Networks (WSN) are The first category of routing protocol is
intended for monitoring an environment. The main the multi-hop flat routing protocols. In flat
task of a wireless sensor node is to sense and networks, each node typically plays the same role
collect data from a certain domain, process them and sensor nodes collaborate together to perform
and transmit it to the sink where the application the sensing task. Due to the large number of such
lies. Areas of applications are like, physical nodes, it is not feasible to assign a global identifier
parameters (e.g., humidity, temperature, light, etc.), to each node. This consideration has led to data
to safety and security-oriented (intrusion detection, centric routing, where the BS sends queries to
natural disaster detection, etc.), to monitor soldiers certain regions and waits for data from the sensors
in the battle field (military applications), patients in located in the selected regions. Since data is being
nursing institutes (e-health applications), fire requested through queries, attribute-based naming
brigades and policemen (security/safety is necessary to specify the properties of data. Early
applications) [1, 6]. works on data centric routing, e.g., SPIN and
The use of potentially unique identifier directed diffusion were shown to save energy
such as the MAC (Medium Access Control) through data negotiation and elimination of
address or the GPS coordinates is not redundant data.
recommended as it forces a significant payload in
the messages. However, this drawback is easily
overcome in wireless sensor networks since an IP
address is not required to identify the destination
node of a specific packet. In fact, attribute-based
addressing fits better with the specificities of
wireless sensor networks. In this case, an attribute
such as node location and sensor type is used to
identify the final destination. Once nodes are
identified, routing protocols are in charge of
constructing and maintaining routes between
distant nodes. The different ways in which routing
protocols operate make them appropriate for
certain applications [6].
Figure1: Routing Protocols in WSN
In general, network structure routing in
WSNs can be divided into flat-based routing,
SPIN:
hierarchical-based routing, and location-based
Sensor Protocols for Information via
routing depending on the envirnoment.
Negotiation (SPIN) that enables a user to query any
In flat-based routing, all nodes are
node and get the required information immediately.
typically assigned equal roles or functionality. In
These protocols make use of the property that
hierarchical-based routing, however, nodes will
nodes in close proximity have similar data, and
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2. National Conference on Current Trends in Computer Science and Engineering - CSECONF2012
hence there is a need to only distribute the data that SPIN-RL: When a channel is lossy, a protocol
other nodes do not posses. The SPIN family of called SPIN-RL is used where adjustments are
protocols uses data negotiation and resource- added to the SPIN-PP protocol to account for the
adaptive algorithms. Nodes running SPIN assign a lossy channel.
high-level name to completely describe their Advantages: Topological changes are localized
collected data (called meta-data) and perform meta- since each node needs to know only its single-hop
data negotiations before any data is transmitted. neighbors. SPIN provides much energy savings
This assures that there is no redundant data sent than flooding and meta-data negotiation almost
throughout the network. The semantics of the meta halves the redundant data. However, SPINs data
data format is application-specific and is not advertisement mechanism cannot guarantee the
specified in SPIN. For example, sensors might use delivery of data. To see this, consider the
their unique IDs to report meta-data if they cover a application of intrusion detection where data
certain known region. In addition, SPIN has access should be reliably reported over periodic intervals
to the current energy level of the node and adapts and assume that nodes interested in the data are
the protocol it is running based on how much located far away from the source node and the
energy is remaining. These protocols work in a nodes between source and destination nodes are not
time-driven fashion and distribute the information interested in that data, such data will not be
all over the network, even when a user does not delivered to the destination at all [2].
request any data. The SPIN family is designed to
address the deficiencies of classic flooding by Directed Diffusion:
negotiation and resource adaptation. The SPIN Directed diffusion is a data-centric (DC)
family of protocols is designed based on two basic and application-aware paradigm in the sense that
ideas: all data generated by sensor nodes is named by
1) Sensor nodes operate more efficiently and attribute-value pairs. The main idea of the DC
conserve energy by sending data that describe the paradigm is to combine the data coming from
sensor data instead of sending all the data; for different sources enroute (in-network aggregation)
example, image and sensor nodes must monitor the by eliminating redundancy, minimizing the number
changes in their energy resources. of transmissions; thus saving network energy and
2) Conventional protocols like flooding or prolonging its lifetime. Unlike traditional end-to-
gossiping based routing protocols waste energy and end routing, DC routing finds routes from multiple
bandwidth when sending extra and un-necessary sources to a single destination that allows in-
copies of data by sensors covering overlapping network consolidation of redundant data.
areas. The drawbacks of flooding include In directed diffusion, sensors measure
implosion, which is caused by duplicate messages events and create gradients of information in their
sent to the same node, overlap when two nodes respective neighborhoods. The base station
sensing the same region will send similar packets requests data by broadcasting interests. Interest
to the same neighbor and resource blindness by describes a task required to be done by the
consuming large amounts of energy without network. Interest diffuses through the network hop-
consideration for the energy constraints. by-hop, and is broad-cast by each node to its
SPIN is a 3-stage protocol as sensor nodes neighbors. As the interest is propagated throughout
use three types of messages ADV, REQ and DATA the network, gradients are setup to draw data
to communicate. ADV is used to advertise new satisfying the query towards the requesting node,
data, REQ to request data, and DATA is the actual i.e., a BS may query for data by disseminating
message itself. The protocol starts when a SPIN interests and intermediate nodes propagate these
node obtains new data that it is willing to share. It interests. Each sensor that receives the interest
does so by broadcasting an ADV message setup a gradient toward the sensor nodes from
containing meta-data. If a neighbor is interested in which it receives the interest. This process
the data, it sends a REQ message for the DATA continues until gradients are setup from the sources
and the DATA is sent to this neighbor node. The back to the BS. More generally, a gradient specifies
neighbor sensor node then repeats this process with an attribute value and a direction. The strength of
its neighbors. As a result, the entire sensor area will the gradient may be different towards different
receive a copy of the data. neighbors resulting in different amounts of
The SPIN family of protocols includes information flow. At this stage, loops are not
many protocols. checked, but are removed at a later stage. Figure2
SPIN-BC: This protocol is designed for broadcast shows an example of the working of directed
channels. diffusion ((a) sending interests, (b) building
SPIN-PP: This protocol is designed for a point to gradients, and (c) data dissemination). When
point communication, i.e., hop-by-hop routing. interests fit gradients, paths of information flow are
SPIN-EC: This protocol works similar to SPIN- formed from multiple paths and then the best paths
PP, but with an energy heuristic added to it. are reinforced so as to prevent further flooding
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according to a local rule. In order to reduce known techniques with special advantages related
communication costs, data is aggregated on the to scalability and efficient communication. As
way. The goal is to find a good aggregation tree such, the concept of hierarchical routing is also
which gets the data from source nodes to the BS. utilized to perform energy-efficient routing in
The BS periodically refreshes and re-sends the WSNs. In a hierarchical architecture, higher energy
interest when it starts to receive data from the nodes can be used to process and send the
source(s). This is necessary because interests are information while low energy nodes can be used to
not reliably transmitted throughout the network. perform the sensing in the proximity of the target.
This means that creation of clusters and assigning
special tasks to cluster heads can greatly contribute
to overall system scalability, lifetime, and energy
efficiency. Hierarchical routing is an efficient way
to lower energy consumption within a cluster and
by performing data aggregation and fusion in order
to decrease the number of transmitted messages to
the BS. Hierarchical routing is mainly two-layer
routing where one layer is used to select cluster
heads and the other layer is used for routing.
LEACH protocol:
Low Energy Adaptive Clustering
Hierarchy (LEACH) is a cluster-based protocol,
which includes distributed cluster formation.
LEACH, randomly selects a few sensor nodes as
cluster-heads (CHs) and rotate this role to evenly
distribute the energy load among the sensors in the
network. In LEACH, the cluster-head (CH) nodes
compress data arriving from nodes that belong to
the respective cluster, and send an aggregated
packet to the base station in order to reduce the
amount of information that must be transmitted to
the base station. LEACH uses a TDMA/CDMA
MAC to reduce inter-cluster and intra-cluster
collisions. However, data collection is centralized
and is performed periodically. Therefore, this
protocol is most appropriate when there is a need
Figure2: Examples of Interest Diffusion in Sensor for constant monitoring by the sensor network. A
Network user may not need all the data immediately. Hence,
periodic data transmissions are unnecessary which
Directed diffusion differs from SPIN in may drain the limited energy of the sensor nodes.
two aspects: After a given interval of time, a randomized
1) Directed diffusion issues on demand rotation of the role of the CH is conducted so that
data queries as the BS send queries to the sensor uniform energy dissipation in the sensor network is
nodes by flooding some tasks. In SPIN, however, obtained. The authors found, based on their
sensors advertise the availability of data allowing simulation model, that only 5% of the nodes need
interested nodes to query that data. to act as cluster heads.
2) All communication in directed The operation of LEACH is separated into
diffusion is neighbor-to-neighbor with each node two phases, the setup phase and the steady state
having the capability of performing data phase.
aggregation and caching. Unlike SPIN, there is no In the setup phase, the clusters are
need to maintain global network topology in organized and CHs are selected. In the steady state
directed diffusion. However, directed diffusion phase, the actual data transfer to the base station
may not be applied to applications (e.g., takes place. The duration of the steady state phase
environmental monitoring) that require continuous is longer than the duration of the setup phase in
data delivery to the BS. order to minimize overhead. During the setup
phase, a predetermined fraction of nodes, p, elect
III. Hierarchical-based Routing Protocols themselves as CHs as follows. A sensor node
chooses a random number, r, between 0 and 1. If
Hierarchical or cluster-based routing, this random number is less than a threshold value,
originally proposed in wireline networks, are well- T(n), the node becomes a cluster-head for the
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current round. The threshold value is calculated fashion. Simulation results showed that PEGASIS
based on an equation that incorporates the desired is able to increase the lifetime of the network twice
percentage to become a cluster-head, the current as much the lifetime of the network under the
round, and the set of nodes that have not been LEACH protocol. Such performance gain is
selected as a cluster-head in the last (1/P) rounds, achieved through the elimination of the overhead
denoted by caused by dynamic cluster formation in LEACH
G. It is given by: and through decreasing the number of
transmissions and reception by using data
aggregation.
Where, G is the set of nodes that are SOP:
involved in the CH election. Each elected CH Self Organizing Protocol is used to build
broadcast an advertisement message to the rest of architecture to support heterogeneous sensors.
the nodes in the network that they are the new These sensors can be mobile or stationary. Some
cluster-heads. All the non-cluster head nodes, after sensors probe the environment and forward the data
receiving this advertisement, decide on the cluster to a designated set of nodes that act as routers.
to which they want to belong to. This decision is Router nodes are stationary and form the backbone
based on the signal strength of the advertisement. for communication. Collected data are forwarded
The non cluster-head nodes inform the appropriate through the routers to the more powerful BS nodes.
cluster-heads that they will be a member of the Each sensing node should be able to reach a router
cluster. After receiving all the messages from the in order to be part of the network. A routing
nodes that would like to be included in the cluster architecture that requires addressing of each sensor
and based on the number of nodes in the cluster, node has been proposed. Sensing nodes are
the cluster-head node creates a TDMA schedule identifiable through the address of the router node
and assigns each node a time slot when it can they are connected to. The routing architecture is
transmit. This schedule is broadcast to all the nodes hierarchical where groups of nodes are formed and
in the cluster. [2]. merge when needed. Local Markov Loops (LML)
algorithm, which performs a random walk on
PEGASIS: spanning trees of a graph, was used to support fault
Power-Efficient Gathering in Sensor tolerance and as a means of broadcasting. Such
Information Systems (PEGASIS) is a near optimal approach is similar to the idea of virtual grid used
chain-based protocol. The basic idea of the in some other protocols that will be discussed later
protocol is that in order to extend network lifetime, under location-based routing protocols. In this
nodes need only communicate with their closest approach, sensor nodes can be addressed
neighbors and they take turns in communicating individually in the routing architecture, and hence
with the base-station. When, the round of all nodes it is suitable for applications where communication
communicating with the base-station ends, a new to a particular node is required. Furthermore, this
round will start and so on. This reduces the power algorithm incurs a small cost for maintaining
required to transmit data per round as the power routing tables and keeping a balanced routing
draining is spread uniformly over all nodes. Hence, hierarchy. It was also found that the energy
PEGASIS has two main objectives: consumed for broadcasting a message is less than
1) Increase the lifetime of each node by that consumed in the SPIN protocol. This protocol,
using collaborative techniques and as a result the however, is not an on-demand protocol especially
network lifetime will be increased. in the organization phase of algorithm. Another
2) Allow only local coordination between issue is related to the formation of hierarchy. It
nodes that are close together so that the bandwidth could happen that there are many cuts in the
consumed in communication is reduced. Unlike network, and hence the probability of applying
LEACH, PEGASIS avoids cluster formation and reorganization phase increases, which will be an
uses only one node in a chain to transmit to the BS expensive operation [2].
instead of using multiple nodes.
To locate the closest neighbor node in VGA:
PEGASIS, each node uses the signal strength to Virtual Grid Architecture routing is an
measure the distance to all neighboring nodes and energy-efficient routing paradigm, proposed in
then adjusts the signal strength so that only one utilizes data aggregation and in-network processing
node can be heard. The chain in PEGASIS will to maximize the network lifetime. A GPS-free
consist of those nodes that are closest to each other approach is used to build clusters that are fixed,
and form a path to the base-station. The aggregated equal, adjacent, and non-overlapping with
form of the data will be sent to the base-station by symmetric shapes. In square clusters were used to
any node in the chain and the nodes in the chain obtain a fixed rectilinear virtual topology. Inside
will take turns in sending to the base-station. The each zone, a node is optimally selected to act as
chain construction is performed in a greedy
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cluster-head. Data aggregation is performed at two certain region rather than sending the interests to
levels: local and then global. The set of cluster- the whole network. By doing this, GEAR can
heads, also called Local Aggregators (LAs), conserve more energy than directed diffusion. Each
perform the local aggregation, while a subset of node in GEAR keeps an estimated cost and a
these Las, are used to perform global aggregation. learning cost of reaching the destination through its
However, the determination of an optimal selection neighbors. The estimated cost is a combination of
of global aggregation points, called Master residual energy and distance to destination. The
Aggregators (MAs), is NP-hard problem. Figure 6 learned cost is a refinement of the estimated cost
illustrates an example of fixed zoning and the that accounts for routing around holes in the
resulting VGA used to perform two level data network. A hole occurs when a node does not have
aggregation. Note that the location of the base any closer neighbor to the target region than itself.
station is not necessarily at the extreme corner of If there are no holes, the estimated cost is equal to
the grid rather it can be located at any arbitrary the learned cost. The learned cost is propagated one
place. hop back every time a packet reaches the
destination so that route setup for next packet will
be adjusted. There are two phases in the algorithm:
1) Forwarding packets towards the target
region: Upon receiving a packet, a node checks its
neighbors to see if there is one neighbor, which is
closer to the target region than itself. If there is
more than one, the nearest neighbor to the target
region is selected as the next hop. If they are all
further than the node itself, this means there is a
hole. In this case, one of the neighbors is picked to
forward the packet based on the learning cost
function. This choice can then be updated
Figure3: Regular shape tessellation applied to the according to the convergence of the learned cost
network area. In each zone, a cluster-head is during the delivery of packets.
selected for local aggregation. Subsets of those 2) Forwarding the packets within the
cluster-heads, called Master nodes, are optimally region: If the packet has reached the region, it can
selected to do global aggregation. be diffused in that region by either recursive
geographic forwarding or restricted flooding.
Restricted flooding is good when the sensors are
IV. Location based routing protocols
not densely deployed. In high-density networks,
In this kind of routing, sensor nodes are recursive geographic flooding is more energy
addressed by means of their locations. The distance efficient than restricted flooding. In that case, the
between neighboring nodes can be estimated on the region is divided into four sub regions and four
basis of incoming signal strengths. Relative copies of the packet are created. This splitting and
coordinates of neighboring nodes can be obtained forwarding process continues until the regions with
by exchanging such information between only one node are left [2].
neighbors. Alternatively, the location of nodes may
be available directly by communicating with a GOAFR:
satellite, using GPS (Global Positioning System), if The Greedy Other Adaptive Face Routing.
nodes are equipped with a small low power GPS The greedy algorithm of GOAFR always picks the
receiver. To save energy, some location based neighbor closest to a node to be next node for
schemes demand that nodes should go to sleep if routing. However, it can be easily stuck at some
there is no activity. More energy savings can be local minimum, i.e. no neighbor is closer to a node
obtained by having as many sleeping nodes in the than the current node. Other Face Routing (OFR) is
network as possible. The problem of designing a variant of Face Routing (FR). The Face Routing
sleep period schedules for each node in a localized (FR) algorithm is the first one that guarantees
manner was addressed in. In the rest of this section, success if the source and the destination are
we review most of the location or geographic based connected. However, the worst-case cost of FR is
routing protocols. proportional to the size of the network in terms of
number of nodes. The first algorithm that can
GEAR:
The protocol, called Geographic and compete with the best route in the worst-case is the
Energy Aware Routing (GEAR), uses energy aware Adaptive Face Routing (AFR) algorithm.
and geographically-informed neighbor selection Moreover, by a lower bound argument, AFR is
heuristics to route a packet towards the destination shown to be asymptotically worst-case optimal. But
region. The key idea is to restrict the number of AFR is not average-case efficient. OFR utilizes the
interests in directed diffusion by only considering a face structure of planar graphs such that the
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6. National Conference on Current Trends in Computer Science and Engineering - CSECONF2012
n
message is routed from node s to node t by protocols in wireless sensor networks which have
traversing a series of face boundaries. The aim is to been presented in the literature.
find the best node on the boundary, i.e., the closest Overall, the routing techniques are
e
node to the destination t by using geometric planes. classified based on the network structure into three
When finished, the algorithm returns to s the best categories: SPIN & Directed Diffusion in Flat Flat-
node on the boundary. The simple greedy based, LEACH, PEGASIS & SOP in Hierarchical
Hierarchical-
algorithm behaves well in dense networks, but it based, SPAN & GOFAR in Location
Location-based.
fails for very simple configurations. It was shown
that GOAFR algorithm can achieve both worst worst- REFERENCES
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Figure 4: Classification and Comparision of
omparision
Routing Protocols in WSN.
V. CONCLUSION
Routing in sensor networks is a new a
area
of research and rapidly growing set of research
results. In this paper, we presented a
comprehensive survey of network structure routing
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