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Transcript
Topologies
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Different topologies may be implemented according to the
application (resemble network topologies)
Topologies that make this discipline a new originate from the need
of building a cost effective application and managing the sensor
network
Each topology has its own benefits, challenges, and tradeoffs
Choosing proper topology to suit the application is the key for the
wireless sensor network
Some topology examples are shown in the following slides
Pritee Parwekar
1
Star Topology
Pritee Parwekar
2
Mesh Topology
Pritee Parwekar
3
Hybrid Star/Mesh Topology
Pritee Parwekar
4
Wireless Sensor Networks
Topology
There are a number of different topologies for
radio communications networks. A brief
discussion of
 the network topologies that apply to wireless
sensor networks are outlined below.
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Star Network (Single Point-to-Multipoint)
A star network is a communications topology
where a single basestation can send and/or
receive a message to a number of remote
nodes.
 The remote nodes can only send or receive a
message from the single basestation, they are
not permitted to send messages to each other.
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Star Network
The advantage of this type of network for
wireless sensor networks is in its simplicity and
the ability to keep the remote node’s power
consumption to a minimum. It also allows for low
latency communications between the remote
node and the basestation.
 The disadvantage of such a network is that the
basestation must be within radio transmission
range of all the individual nodes and is not as
robust as other networks due to its dependency
on a single node to manage the network.
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Star Network Topology
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Star Topology
A classical star topology of WSANs was studied in
Korber et al. (2007).In the star topology, the BS
serves as a network controller and as a
gateway to upper layers. The BS may have a
wired bus and a wireless radio interface.
 The TDMA (time division multiple access)
technique is employed in the MAC layer.
 Each sensor is integrated into an actuator to
form a sensor-actuator module. These
modules are able to reach the BS in one-hop
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An example in military applications.
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Mesh Network
A mesh network allows for any node in the
network to transmit to any other node in the
network that is within
 its radio transmission range. This allows for
what is
 known as multihop communications; that is, if
a node
 wants to send a message to another node that
is out of radio communications range, it can
use an intermediate node to forward the
message to the desired node. This network
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Mesh Topology
Advantage of redundancy and scalability.
 If an individual node fails, a remote node
still can communicate to any other node
in its range, which in turn, can forward the
message to the desired location. In
addition, the range of the network is not
necessarily limited by the range in
between single nodes, it can simply be
extended by adding more nodes to the
system.
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Mesh Topology
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Disadvantage of this type of network is in
power consumption for the nodes that
implement the multihop communications
are generally higher than for the nodes
that don’t have this capability,often
limiting the battery life. Additionally, as the
number of communication hops to a
destination increases,the time to deliver
the message also increases, especially if
low power operation of the nodes is a
requirement.
Mesh Topology
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Hybrid Star – Mesh Network
A hybrid between the star and mesh network
provides for a robust and versatile
communications network, while maintaining
the ability to keep the wireless sensor nodes
power consumption to a minimum.
 In this network topology, the lowest power
sensor nodes are not enabled with the ability
to forward messages. This allows for minimal
power consumption to be maintained.
However, other nodes on the network are
enabled with multihop capability, allowing

Shubhalaxmi Kher, Arkansas State University
15
Hybrid Topology
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Generally, the nodes with the multihop
capability
are higher power, and if possible, are
often plugged into the electrical mains
line. This is the topology
implemented by the up and coming mesh
networking standard known as ZigBee.
Hybrid Topology
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Crossbow Software Framework
Pritee Parwekar
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Full power network topology
Reduced network topology via Minimal Spanning Tree
(Change in Tx Range)
Reduced network topology via Connected Dominating Set
(Select a subset of nodes that cover all the network and
turn off non-selected nodes)
Topology maintenance algorithms
In the same manner as topology
construction, there are many ways to
perform topology maintenance:
 Global Vs. Local
 Dynamic Vs. Static Vs. Hybrid
 Triggered by time, energy, density, random,
etc.
Global
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DGTRec (Dynamic Global Topology Recreation):
Periodically, wake up all inactive nodes, reset the existing reduced
topology in the network and apply a topology construction
protocol.
SGTRot (Static Global Topology Rotation):
Initially, the topology construction protocol must create more than
one reduced topology (hopefully as disjoint as possible). Then,
periodically, wake up all inactive nodes, and change the current
active reduced topology to the next.
HGTRotRec (Hybrid Global Topology Rotation and
Recreation)
Work as the SGTRot, but when the current active reduced
topology detects a certain level of disconnection, reset the reduced
topology and invoke the topology construction protocol to
recreate that particular reduced topology.
Local
DL-DSR (Dynamic Local DSR-based
TM)
 This protocol, based on the Dynamic
Source Routing (DSR) routing algorithm,
recreates the paths of disconnected
nodes when a node fails.
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Topology construction algorithms
There are many ways to perform topology
construction:
Change the transmission range of the
nodes
 Turn off nodes from the network
 Create a communication backbone
 Clustering, etc.
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Some examples of topology construction
algorithms are:
Tx range-based
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Geometry-based: Gabriel graph (GG), Relative neighborhood
graph (RNG)
Spanning Tree Based
Direction Based: Nearest neighbor graph, Cone Based Topology
Control (CBTC), Distributed RNG
Neighbor based
Routing based:
Hierarchical
CDS-based(connected dominating set)
Cluster-based: Low Energy Adaptive Clustering Hierarchy
Topology construction and maintenance
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Topology control have been divided into
two subproblems: topology
construction, in charge of the initial
reduction, and topology maintenance,
in charge of the maintenance of the
reduced topology so characteristics like
connectivity and coverage are preserved.
Topology construction and
maintenance
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This is the first stage of a topology control protocol. Once
the initial topology is deployed, specially when the location of
the nodes is random, the administrator has no control over
the design of the network; for example, some areas may be
very dense, showing a high number of redundant nodes,
which will increase the number of message collisions and will
provide several copies of the same information from similarly
located nodes. However, the administrator has control over
some parameters of the network: transmission power of the
nodes, state of the nodes (active or sleeping), role of the
nodes (Clusterhead, gateway, regular), etc. By modifying this
parameters, the topology of the network can change.
construction and maintenance

After some time being active, some nodes
will start to run out of energy. Especially
in wireless sensor networks with
multihoping, it is a fact that nodes that are
closer to the sink spend higher amounts
of energy that those farther away due to
packet forwarding. The network must
restore the reduce network periodically
in order to preserve connectivity,
coverage, density the application requires.
construction and maintenance

Topology control is a technique used
mainly in wireless ad hoc and sensor
networks to reduce the initial topology of
the network in order to save energy, cut
down interference and extend the lifetime
of the network. The main goal is to
reduce the number of active nodes and
active links, preserving the saved
resources for future maintenance.
The minimum spanning tree of a planar graph.
Each edge is labeled with its weight, which
here is roughly proportional to its length.
The number and nature of links that are to be
used among all potentially available links can
be controlled. Topology control can be
achieved by modifying the transmission radii,
selecting a given subset of the links, or moving
some nodes (if such functionality is available).
 A general approach employed in data
gathering and data aggregation is to construct
a spanning tree which is rooted at the sink
and connects all sensor nodes in the network.
If one node fails, the topology will be
reorganized into a
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Current problems at the network layer can be classified
into three categories:
topology control, routing, and coordination.
A well-organized network topology can not
only prolong the lifetime of a network, but
also enhance data communications.
 Topology control problems can be subdivided
into neighbor discovery problems and
network organization problems.
 Neighbor discovery problems are defined as
problems in detecting and discovering
neighbors which are located within the
transmission range.
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