U N I T - 8

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U N I T - 8

• Wireless Sensor Networks

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Contents

• Wireless Sensor Networks (WSN)
• Wireless Mess Networks (WMN)
• Computational Grids
• P2P Networks
• Session Initiation Protocol (SIP)
• HTML5

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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.

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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.

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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.

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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.

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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.

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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 memoryoff-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-to-reach 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.

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WSN Functioning Architecture
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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.
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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).
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WSN Characteristics

• The main characteristics of a WSN include
• 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

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WSN Operations

• Five stages
• Planning
• Deployment
• Post Deployment
• Operation
• Post Operation

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WSN Design Process

• The following issues should be considered during
  design of WSN
• Routing Protocol Issues
• Data Dissemination
• Query Processing
• Location and Management Issues
• Key Distribution
• Security Measures
• MAC Protocol Issues.

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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,
• The Setup Phase
• The Steady State Phase.

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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.

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Sensor Architecture Cluster Management

• The setup phase procedure is as follows
• At the beginning of each round, each node
  advertises its probability to the CH, to all
  other nodes.
• Nodes with higher probabilities are chosen as the
  CHs.
• CHs broadcast an advertisement message (ADV)
  using CSMA MAC protocol.
• Based on the signal strength, each non-CH node
  determines its CH for this round.
• Each non-CH transmits a join-request message
  (join-REQ) back to its chosen CH using a CSMA MAC
  protocol.
• CH node sets up a time division multiple access
  (TDMA) schedule for data transmission
  coordination with in the cluster.

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Sensor Architecture Cluster Management

• The steady state phase procedure for data
  transmission is as follows
• TDMA schedule is used to send data from
  node-to-head cluster.
• Head cluster aggregates the data received from
  node to cluster.
• Communication is via direct sequence spread
  spectrum (DSSS) and each cluster uses a unique
  spreading code to reduce inter-cluster-interferenc
  e.
• 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.

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Sensor Architecture Cluster Management
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Wireless Mess Networks
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Wireless Mess Networks

• Characteristics
• WMN support ad-hoc networking, and have the
  capability of self-forming, self-healing, and
  self-organization.
• WMNs are multihop wireless, but with a wireless
  infrastructure/backbone provided by mesh routers.
• Mesh routers have minimal mobility and perform
  dedicated routing and configuration which
  significantly decreases the load of mesh clients
  and other end nodes.
• Mobility of end nodes in supported easily through
  the wireless infrastructure.
• Mesh routers integrate heterogeneous network,
  including both wired and wireless networks.
• WMNs are not stand alone and need to be
  compatible and interoperable with other wireless
  networks.

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WMN Design
Internet
Wireless Client
Mesh Router with Gateway/ Bridge
Wired Client
Wireless Mesh Backbone
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Wireless Mess Networks

• Issues in WMNs
• Physical Layer Issues.
• MAC Sub Layer Issues.
• Network Layer Issues.
• Transport Layer Issues.

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Wireless Mess Networks

• Issues in WMNs Physical Layer Issues
• 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.
• 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.
• 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.

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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,
• 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.

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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.
• Multipath Routing
• -- for better load balancing.
• -- high fault tolerance.
• -- complexity (drawback).
• 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.
• Hierarchical Routing

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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.

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Computational Grids
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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.

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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.

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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.