UNIT-8
Wireless
Sensor
Networks
Contents…
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Wireless Sensor Networks (WSN)
Wireless Mess Networks (WMN)
Computational Grids
P2P Networks
Session Initiation Protocol (SIP)
HTML5
Wireless Sensor Networks (WSN)
• A wireless sensor network is a collection of
self-organized sensing nodes grouped in a
network.
• A wireless sensor network (WSN) consists of
spatially distributed autonomous sensors to
monitor physical or environmental conditions,
such as temperature, sound, pressure, etc.
and to cooperatively pass their data through
the network to a main location.
Wireless Sensor Networks (WSN)
A sensor node,
also known as a
mote, is a node in
a wireless sensor
network that is
capable of
performing some
processing,
gathering sensory
information and
communicating
with other
connected nodes
in the network.
Wireless Sensor Networks (WSN)
on the basis of mode of operation and type of
intended applications, WSN can be broadly
classified in to 2 categories:
Proactive WSN: The sensor nodes periodically
switch on their transmitters, sense the parameter,
and transmit the data to the network.
Reactive WSN: The sensor nodes react
immediately to sudden and significant changes in
the value of a sensed parameter.
WSN Functioning:
Components:
The main components of a sensor node are a microcontroller,
transceiver, external memory, power source and one or more
sensors.
Controller
• The controller performs tasks, processes data and controls the
functionality of other components in the sensor node.
• While the most common controller is a microcontroller, other
alternatives that can be used as a controller are: a general purpose
desktop microprocessor, digital signal processors, ect.
• A microcontroller is often used in many embedded systems such as
sensor nodes because of its low cost, flexibility to connect to other
devices, ease of programming, and low power consumption.
WSN Functioning:
Components: Transceiver
• Sensor nodes often make use of ISM band, which gives free radio,
spectrum allocation and global availability.
• The possible choices of wireless transmission media are radio
frequency (RF), optical communication (laser) and infrared.
• Lasers require less energy , but need line-of-sight for
communication and are sensitive to atmospheric conditions.
• Infrared, like lasers, needs no antenna but it is limited in its
broadcasting capacity.
• Radio frequency-based communication is the most relevant that fits
most of the WSN applications. WSNs tend to use license-free
communication frequencies: 173, 433, 868, and 915 MHz; and 2.4
GHz.
• The functionality of both transmitter and receiver are combined
into a single device known as a transceiver.
WSN Functioning:
Components: External memory
• From an energy perspective, the most relevant kinds of memory are the
on-chip memory of a microcontroller and Flash memory—off-chip RAM is
rarely, if ever, used.
• Flash memories are used due to their cost and storage capacity. Memory
requirements are very much application dependent.
Components: Power source
• A wireless sensor node is a popular solution when it is difficult or
impossible to run a mains supply to the sensor node.
• However, since the wireless sensor node is often placed in a hard-toreach location, changing the battery regularly can be costly and
inconvenient.
• The sensor node consumes power for sensing, communicating and data
processing. More energy is required for data communication than any
other process. The energy cost of transmitting 1 Kb a distance of 100
metres is approximately the same as that used for the execution of 3
million instructions by a 100 million instructions per second/W processor.
WSN Functioning: Architecture
WSN: Operating System support in Sensor Devices
As sensor nodes must be low power, their hardware design will
tradeoff computation capabilities for lower power consumption.
As such, the nodes will have limited processing power and
memory resources.
An operating system for sensor networks should deliver the
required application services without using a significant amount
of the computational resources available to the nodes.
Typical embedded operating systems, such as TinyOS, VxWorks,
QNX, OS-9, WinCE and Clinux provide a programming
environment similar to those existing in traditional computers.
WSN: Operating System support in Sensor Devices
TinyOS is based on an event driven programming model instead
of multithreading. TinyOS programs are composed in to event
handlers and tasks which run to completion semantics.
When an external event occurs, such as an incoming packet or a
sensor reading, TinyOS calls the appropriate event handler to
handle the event.
Both the TinyOS system and programs written for TinyOS are
written in a special programming language called network
embedded systems C (nesC).
WSN Characteristics:
The main characteristics of a WSN include:
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Power consumption constrains for nodes using batteries or
energy harvesting
Ability to cope with node failures
Mobility of nodes
Communication failures
Heterogeneity of nodes
Scalability to large scale of deployment
Ability to withstand harsh environmental conditions
Ease of use
WSN Operations:
Five stages:
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Planning
Deployment
Post Deployment
Operation
Post Operation
WSN Design Process:
The following issues should be considered during design of WSN
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Routing Protocol Issues
Data Dissemination
Query Processing
Location and Management Issues
Key Distribution
Security Measures
MAC Protocol Issues.
Sensor Architecture Cluster Management:
Low Energy Adaptive Clustering Hierarchy (LEACH) a clustered
based protocol that minimizes energy dissipation in sensor
networks.
The purpose of LEACH is to randomly select sensor nodes as
Cluster Heads (CHs), so the high energy dissipation in
communicating with the base station is spread to all sensor
nodes in the sensor network.
The operation of LEACH is separated into 2 phases,
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The Setup Phase
The Steady State Phase.
Sensor Architecture Cluster Management:
• Each setup phase consists of CH selection and
cluster formation.
• Steady state phase consists of the data transmission.
• The duration of the steady state phase is longer
than that of the setup phase to minimize the
overhead.
Sensor Architecture Cluster Management:
The setup phase procedure is as follows:
1. At the beginning of each round, each node advertises its
probability to the CH, to all other nodes.
2. Nodes with higher probabilities are chosen as the CHs.
3. CHs broadcast an advertisement message (ADV) using CSMA
MAC protocol.
4. Based on the signal strength, each non-CH node determines
its CH for this round.
5. Each non-CH transmits a join-request message (join-REQ)
back to its chosen CH using a CSMA MAC protocol.
6. CH node sets up a time division multiple access (TDMA)
schedule for data transmission coordination with in the
cluster.
Sensor Architecture Cluster Management:
The steady state phase procedure for data transmission is as
follows:
1. TDMA schedule is used to send data from node-to-head cluster.
2. Head cluster aggregates the data received from node to cluster.
3. Communication is via direct sequence spread spectrum (DSSS)
and each cluster uses a unique spreading code to reduce intercluster-interference.
4. Data are sent from the CH nodes to the BS using a fixed
spreading code and CSMA.
After a certain period of time spent on the steady state phase,
the network goes into the setup phase again enters another
round of selecting CHs.
Sensor Architecture Cluster Management:
M
M
M
CH
M
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M
CH
M
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CH
M
M
Wireless Mess Networks
Wireless Mess Networks
Characteristics:
1. WMN support ad-hoc networking, and have the capability
of self-forming, self-healing, and self-organization.
2. WMNs are multihop wireless, but with a wireless
infrastructure/backbone provided by mesh routers.
3. Mesh routers have minimal mobility and perform
dedicated routing and configuration which significantly
decreases the load of mesh clients and other end nodes.
4. Mobility of end nodes in supported easily through the
wireless infrastructure.
5. Mesh routers integrate heterogeneous network, including
both wired and wireless networks.
6. WMNs are not stand alone and need to be compatible
and interoperable with other wireless networks.
WMN Design:
Internet
Wireless
Client
Mesh Router
with Gateway/
Bridge
Wireless Mesh Backbone
Wired
Client
Wireless Mess Networks
Issues in WMNs:
1.
2.
3.
4.
Physical Layer Issues.
MAC Sub Layer Issues.
Network Layer Issues.
Transport Layer Issues.
Wireless Mess Networks
Issues in WMNs: Physical Layer Issues:
1.
IEEE 802.11 Mesh Networks
-- peak load is 11 Mbps (802.11b).
-- 54 Mbps (802.11a).
-- Researchers interested to increase the speed of Wi-Fi by 10 to 20 times.
2.
IEEE 802.15 Mesh Networks
--802.15.3a is based on multiband Orthogonal frequency-division
multiplexing(OFDM), that uses ultra wide band(UWB) to reach up to 480 Mbps.
-- a direct sequence UWB (DS-UWB) claims up to 1.3 Gbps.
3.
IEEE 802.16 Mesh Networks
-- 802.16 operates in the 1066 GHz band and requires line of sight
towers.
-- The 802.16a extension uses lower frequency of 211 GHz, enabling
non line of sight connections.
-- to allow consumers to connect to the internet while moving at
vehicular speed, 802.16e is used.
Wireless Mess Networks
Issues in WMNs: MAC Sub Layer Issues:
MAC layer is concerned with more than One Hop (OH)
communication in WMN. MAC layer works for multipoint to
multipoint and network self organization.
Differences between the MAC in WMN and other types of networks
are,
1.
2.
3.
4.
MAC for WMNs is concerned with more than OH communication.
MAC distributive, needs to be collaborative, and works for multipoint to
multipoint communication.
Self organization of the network is needed for better collaboration
between neighboring nodes and nodes in multi-hop distances.
Mobility is low but still affects the performance of MAC.
Wireless Mess Networks
Issues in WMNs: Network Layer Issues:
WMN is tightly integrated with the Internet and IP.
Routing protocols for WMN are different from those in wired
network.
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Multipath Routing
-- for better load balancing.
-- high fault tolerance.
-- complexity (drawback).
2.
Multiradio Routing
-- focuses on maximizing throughput rather than mobility or minimizing energy.
-- shortest path routing algorithms are used.
-- NIC is replaced with Multiradio NIC.
-- for multiradio WMN, multiradio link quality source routing (MR-LQSR) is used.
3.
Hierarchical Routing
Wireless Mess Networks
Issues in WMNs: Transport Layer Issues:
• The WMN use single channel for data transfer
and control, and these are multi-hop networks.
• packet loses at higher bit rates.
• the hidden node and exposed node causes
transmission failure.
• TCP is not suitable, because client moves across
the network.
• UDP alone can not guarantee the delivery of
packets.
• Real-Time Protocol (RTP) is used along with UDP.
Computational Grids
Computational Grids
• A computational grid is a loose network of
computers linked to perform grid computing.
• A large computational task is divided up among
individual machines, which run calculations in
parallel and then return results to the original
computer. These individual machines are nodes in
the network.
• Computational grids are often more cost effective
than supercomputer of equal computing power.
Computational Grids
Grid Features:
Computational grids are used to solve the
problems in engineering, science and commerce.
• Provides transparent access to remote resources.
• Enable resource sharing.
• Reduce execution time for data processing
applications.
• Allow on-demand aggregation of resources at
multiple sites.
• Provides access to remote database and
software.
Computational Grids
Issues in Grid Construction Design:
For data grids:
• The ability to integrate multiple distributed,
heterogeneous, and independently managed data sources.
• The ability to provide efficient data transfer mechanisms to
provide data where the computation will take place.
• The ability to provide necessary data discovery mechanism,
which allow the user to find data based on characteristics
of data.
• The capability to implement data encryption and integrity
checks to ensure that data is transported across the
network in a secure fashion.
• The ability to provide the backup/restore mechanism and
policies necessary to prevent data loss and minimize
unplanned downtime across the grid.