A Wireless Sensor Network

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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. The more modern networks are bi-directional, also enabling control of sensor activity. The development of wireless sensor networks was motivated by military applications such as battlefield surveillance; today such networks are used in many industrial and consumer applications, such as industrial process monitoring and control, machine health monitoring, and so on. The WSN is built of "nodes" – from a few to several hundreds or even thousands, where each node is connected to one (or sometimes several) sensors. Each such sensor network node has typically several parts: a radio transceiver with an internal antenna or connection to an external antenna, a microcontroller, an electronic circuit for interfacing with the sensors and an energy source, usually a battery or an embedded form of energy harvesting. A sensor node might vary in size from that of a shoebox down to the size of a grain of dust, although functioning "motes" of genuine microscopic dimensions have yet to be created. The cost of sensor nodes is similarly variable, ranging from a few to hundreds of dollars, depending on the complexity of the individual sensor nodes. Size and cost constraints on sensor nodes result in corresponding constraints on resources such as energy, memory, computational speed and communications bandwidth. The topology of the WSNs can vary from a simple star network to an advanced multi-hop wireless mesh network. The propagation technique between the hops of the network can be routing or flooding.[1][2] In computer science and telecommunications, wireless sensor networks are an active research area with numerous workshops and conferences arranged each year.

Contents


1 Applications o 1.1 Area monitoring
o

1.2 Environmental/Earth monitoring
     

1.2.1 Air quality monitoring 1.2.2 Air pollution monitoring 1.2.3 Forest fire detection 1.2.4 Landslide detection 1.2.5 Water quality monitoring 1.2.6 Natural disaster prevention

o

1.3 Industrial monitoring
 

1.3.1 Machine health monitoring 1.3.2 Data logging

  o o o • •

1.3.3 Industrial sense and control applications 1.3.4 Water/Waste water monitoring

1.4 Agriculture 1.5 Passive localization and tracking 1.6 Smart home monitoring

2 Characteristics 3 Platforms
o o o

3.1 Standards and specifications 3.2 Hardware 3.3 Software


3.3.1 Operating systems

o • •

3.4 Online collaborative sensor data management platforms

4 Simulation of WSNs 5 Other concepts
o o o

5.1 Distributed sensor network 5.2 Data integration and Sensor Web 5.3 In-network processing

• • •

6 See also 7 References 8 External links

Applications
Area monitoring
Area monitoring is a common application of WSNs. In area monitoring, the WSN is deployed over a region where some phenomenon is to be monitored. A military example is the use of sensors detect enemy intrusion; a civilian example is the geo-fencing of gas or oil pipelines.

Environmental/Earth monitoring

The term Environmental Sensor Networks has evolved to cover many applications of WSNs to earth science research.[3] This includes sensing volcanoes,[4] oceans,[5] glaciers,[6] forests,[7] etc. Some of the major areas are listed below. Air quality monitoring The degree of pollution in the air has to be measured frequently in order to safeguard people and the environment from any kind of damages due to air pollution. In dangerous surroundings, real time monitoring of harmful gases is a concerning process because the weather can change with severe consequences in an immediate manner. Fortunately, wireless sensor networks have been launched to produce specific solutions for people.[8]


Interior monitoring

Observing the gas levels at vulnerable areas needs the usage of high-end, sophisticated equipment, capable to satisfy industrial regulations. Wireless internal monitoring solutions facilitate keep tabs on large areas as well as ensure the precise gas concentration degree.


Exterior monitoring

External air quality monitoring needs the use of precise wireless sensors, rain & wind resistant solutions as well as energy reaping methods to assure extensive liberty to machine that will likely have tough access. Air pollution monitoring Wireless sensor networks have been deployed in several cities (Stockholm, London and Brisbane) to monitor the concentration of dangerous gases for citizens. These can take advantage of the ad-hoc wireless links rather than wired installations, which also make them more mobile for testing readings in different areas. There are various architectures that can be used for such applications as well as different kinds of data analysis and data mining that can be conducted.[9] Forest fire detection A network of Sensor Nodes can be installed in a forest to detect when a fire has started. The nodes can be equipped with sensors to measure temperature, humidity and gases which are produced by fire in the trees or vegetation. The early detection is crucial for a successful action of the firefighters; thanks to Wireless Sensor Networks, the fire brigade will be able to know when a fire is started and how it is spreading. Landslide detection A landslide detection system makes use of a wireless sensor network to detect the slight movements of soil and changes in various parameters that may occur before or during a landslide. Through the data gathered it may be possible to know the occurrence of landslides long before it actually happens.[10]

Water quality monitoring Water quality monitoring involves analyzing water properties in dams, rivers, lakes & oceans, as well as underground water reserves.[11] The use of many wireless distributed sensors enables the creation of a more accurate map of the water status, and allows the permanent deployment of monitoring stations in locations of difficult access, without the need of manual data retrieval. Natural disaster prevention Wireless sensor networks can effectively act to prevent the consequences of natural disasters, like floods. Wireless nodes have successfully been deployed in rivers where changes of the water levels have to be monitored in real time.

Industrial monitoring
Machine health monitoring Wireless sensor networks have been developed for machinery condition-based maintenance (CBM) as they offer significant cost savings and enable new functionality. In wired systems, the installation of enough sensors is often limited by the cost of wiring. Previously inaccessible locations, rotating machinery, hazardous or restricted areas, and mobile assets can now be reached with wireless sensors. Data logging Main article: Data logging Wireless sensor networks are also used for the collection of data for monitoring of environmental information, this can be as simple as the monitoring of the temperature in a fridge to the level of water in overflow tanks in nuclear power plants. The statistical information can then be used to show how systems have been working. The advantage of WSNs over conventional loggers is the "live" data feed that is possible. Industrial sense and control applications In recent research a vast number of wireless sensor network communication protocols have been developed. While previous research was primarily focused on power awareness, more recent research have begun to consider a wider range of aspects, such as wireless link reliability,[12] realtime capabilities,[13] or quality-of-service. These new aspects are considered as an enabler for future applications in industrial and related wireless sense and control applications, and partially replacing or enhancing conventional wire-based networks by WSN techniques. Water/Waste water monitoring Monitoring the quality and level of water includes many activities such as checking the quality of underground or surface water and ensuring a country’s water infrastructure for the benefit of

both human and animal. The area of water quality monitoring utilizes wireless sensor networks and many manufacturers have launched fresh and advanced applications for the purpose.[14]


Observation of water quality

The whole process includes examining water properties in rivers, dams, oceans, lakes and also in underground water resources. Wireless distributed sensors let users to make a precise map of the water condition as well as making permanent distribution of observing stations in areas of difficult access with no manual data recovery.


Water distribution network management

Manufacturers of water distribution network sensors concentrate on observing the water management structures such as valve and pipes and also making remote access to water meter readings.


Preventing natural disaster

The consequences of natural perils like floods can be effectively prevented with wireless sensor networks. Wireless nodes are distributed in rivers so that changes of the water level can be effectively monitored.

Agriculture
Using wireless sensor networks within the agricultural industry is increasingly common; using a wireless network frees the farmer from the maintenance of wiring in a difficult environment. Gravity feed water systems can be monitored using pressure transmitters to monitor water tank levels, pumps can be controlled using wireless I/O devices and water use can be measured and wirelessly transmitted back to a central control center for billing. Irrigation automation enables more efficient water use and reduces waste.[15]


Accurate agriculture

Wireless sensor networks let users to make precise monitoring of the crop at the time of its growth. Hence, farmers can immediately know the state of the item at all its stages which will ease the decision process regarding the time of harvest.


Irrigation management

When real time data is delivered, farmers are able to achieve intelligent irrigation. Data regarding the fields such as temperature level and soil moisture are delivered to farmers through wireless sensor networks. When each plant is joined with a personal irrigation system, farmers can pour the precise amount of water each plant needs and hence, reduce the cost and improve the quality of the end product. The networks can be employed to manage various actuators in the systems using no wired infrastructure.



Greenhouses

Wireless sensor networks are also used to control the temperature and humidity levels inside commercial greenhouses. When the temperature and humidity drops below specific levels, the greenhouse manager must be notified via e-mail or cell phone text message, or host systems can trigger misting systems, open vents, turn on fans, or control a wide variety of system responses. Recent research in wireless sensor networks in agriculture industry give emphasis on its use in greenhouses, particularly for big exploitations with definite crops. Such microclimatic ambiances need to preserve accurate weather status at all times. Moreover, using multiple distributed sensors will better control the above process, in open surface as well as in the soil.

Passive localization and tracking
The application of WSN to the passive localization and tracking of non-cooperative targets (i.e., people not wearing any tag) has been proposed by exploiting the pervasive and low-cost nature of such technology and the properties of the wireless links which are established in a meshed WSN infrastructure.[16]

Smart home monitoring
Monitoring the activities performed in a smart home is achieved using wireless sensors embedded within everyday objects forming a WSN.[17] State changes to objects based on human manipulation is captured by the wireless sensors network enabling activity-support services.[18]

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

Sensor nodes can be imagined as small computers, extremely basic in terms of their interfaces and their components. They usually consist of a processing unit with limited computational power and limited memory, sensors or MEMS (including specific conditioning circuitry), a

communication device (usually radio transceivers or alternatively optical), and a power source usually in the form of a battery. Other possible inclusions are energy harvesting modules, secondary ASICs, and possibly secondary communication interface (e.g. RS-232 or USB). The base stations are one or more components of the WSN with much more computational, energy and communication resources. They act as a gateway between sensor nodes and the end user as they typically forward data from the WSN on to a server. Other special components in routing based networks are routers, designed to compute, calculate and distribute the routing tables.

Platforms
Standards and specifications
Several standards are currently either ratified or under development by organizations including WAVE2M for wireless sensor networks. There are a number of standardization bodies in the field of WSNs. The IEEE focuses on the physical and MAC layers; the Internet Engineering Task Force works on layers 3 and above. In addition to these, bodies such as the International Society of Automation provide vertical solutions, covering all protocol layer. Finally, there are also several non-standard, proprietary mechanisms and specifications. Standards are used far less in WSNs than in other computing systems which makes most systems incapable of direct communication between different systems. However predominant standards commonly used in WSN communications include:
• • • • •

WirelessHART IEEE 1451 ZigBee / 802.15.4 ZigBee IP 6LoWPAN

Hardware
Main article: sensor node One major challenge in a WSN is to produce low cost and tiny sensor nodes. There are an increasing number of small companies producing WSN hardware and the commercial situation can be compared to home computing in the 1970s. Many of the nodes are still in the research and development stage, particularly their software. Also inherent to sensor network adoption is the use of very low power methods for data acquisition.

Software

Energy is the scarcest resource of WSN nodes, and it determines the lifetime of WSNs. WSNs are meant to be deployed in large numbers in various environments, including remote and hostile regions, where ad-hoc communications are a key component. For this reason, algorithms and protocols need to address the following issues:
• • •

Lifetime maximization Robustness and fault tolerance Self-configuration

Lifetime maximization: Energy/Power Consumption of the sensing device should be minimized and sensor nodes should be energy efficient since their limited energy resource determines their lifetime. To conserve power the node should shut off the radio power supply when not in use. Some of the important topics in WSN(Wireless Sensor Networks) software research are:
• • •

Operating systems Security Mobility

Operating systems Operating systems for wireless sensor network nodes are typically less complex than generalpurpose operating systems. They more strongly resemble embedded systems, for two reasons. First, wireless sensor networks are typically deployed with a particular application in mind, rather than as a general platform. Second, a need for low costs and low power leads most wireless sensor nodes to have low-power microcontrollers ensuring that mechanisms such as virtual memory are either unnecessary or too expensive to implement. It is therefore possible to use embedded operating systems such as eCos or uC/OS for sensor networks. However, such operating systems are often designed with real-time properties. TinyOS is perhaps the first[19] operating system specifically designed for wireless sensor networks. TinyOS is based on an event-driven programming model instead of multithreading. TinyOS programs are composed of event handlers and tasks with run-to-completion semantics. When an external event occurs, such as an incoming data packet or a sensor reading, TinyOS signals the appropriate event handler to handle the event. Event handlers can post tasks that are scheduled by the TinyOS kernel some time later. LiteOS is a newly developed OS for wireless sensor networks, which provides UNIX-like abstraction and support for the C programming language. Contiki is an OS which uses a simpler programming style in C while providing advances such as 6LoWPAN and Protothreads.

RIOT implements a microkernel architecture. It provides multithreading with standard API and allows for development in C/C++. RIOT supports common IoT protocols such as 6LoWPAN, IPv6, RPL, TCP, and UDP.[20]

Online collaborative sensor data management platforms
Online collaborative sensor data management platforms are on-line database services that allow sensor owners to register and connect their devices to feed data into an online database for storage and also allow developers to connect to the database and build their own applications based on that data. Examples include Xively and the Wikisensing platform. Such platforms simplify online collaboration between users over diverse data sets ranging from energy and environment data to collected from transport services. Other services include allowing developers to embed real-time graphs & widgets in websites; analyse and process historical data pulled from the data feeds; send real-time alerts from any datastream to control scripts, devices and environments. The architecture of the Wikisensing system is described in [21] describes the key components of such systems to include APIs and interfaces for online collaborators, a middleware containing the business logic needed for the sensor data management and processing and a storage model suitable for the efficient storage and retrieval of large volumes of data.

Simulation of WSNs
At present, agent-based modeling and simulation is the only paradigm which allows the simulation of complex behavior in the environments of wireless sensors (such as flocking).[22] Agent-based simulation of wireless sensor and ad-hoc networks is a relatively new paradigm. Agent-based modelling was originally based on social simulation. Network simulators like OPNET, NetSim and NS2 can be used to simulate a wireless sensor network.

Other concepts
Distributed sensor network
If a centralised architecture is used in a sensor network and the central node fails, then the entire network will collapse, however the reliability of the sensor network can be increased by using a distributed control architecture. Distributed control is used in WSNs for the following reasons: 1. Sensor nodes are prone to failure, 2. For better collection of data 3. To provide nodes with backup in case of failure of the central node There is also no centralised body to allocate the resources and they have to be self organised.

Data integration and Sensor Web
The data gathered from wireless sensor networks is usually saved in the form of numerical data in a central base station. Additionally, the Open Geospatial Consortium (OGC) is specifying standards for interoperability interfaces and metadata encodings that enable real time integration of heterogeneous sensor webs into the Internet, allowing any individual to monitor or control Wireless Sensor Networks through a Web Browser.

In-network processing
To reduce communication costs some algorithms remove or reduce nodes redundant sensor information and avoid forwarding data that is of no use. As nodes can inspect the data they forward they can measure averages or directionality for example of readings from other nodes. For example, in sensing and monitoring applications, it is generally the case that neighbouring sensor nodes monitoring an environmental feature typically register similar values. This kind of data redundancy due to the spatial correlation between sensor observations inspires the techniques for in-network data aggregation and mining.

See also
• • • • • •

Ad Hoc On-Demand Distance Vector Routing Ambient intelligence Backpressure routing List of ad-hoc routing protocols MQ Telemetry Transport Sensor grid

References
1. ^ Dargie, W. and Poellabauer, C., "Fundamentals of wireless sensor networks: theory and practice", John Wiley and Sons, 2010 ISBN 978-0-470-99765-9, pp. 168–183, 191–192 2. ^ Sohraby, K., Minoli, D., Znati, T. "Wireless sensor networks: technology, protocols, and applications, John Wiley and Sons", 2007 ISBN 978-0-471-74300-2, pp. 203–209 3. 4. ^ Hart, J. K. and Martinez, K. (2006) Environmental Sensor Networks:A revolution in the earth system science? Earth-Science Reviews, 78 . pp. 177-191. ^ G. Werner-Allen, K. Lorincz, M. Welsh, O. Marcillo, J. Johnson, M. Ruiz, J. Lees, "Deploying a Wireless Sensor Network on an Active Volcano," IEEE Internet Computing, vol. 10, no. 2, pp. 18-25, 2006

5.

^ I. Vasilescu, K. Kotay, D. Rus, M. Dunbabin, and P. Corke. 2005. Data collection, storage, and retrieval with an underwater sensor network. In Proceedings of the 3rd international conference on Embedded networked sensor systems (SenSys '05. ACM, New York, NY, USA, 154-165. ^ Martinez, K, Hart, J. K. and Ong, R (2009) Deploying a Wireless Sensor Network in Iceland. Lecture Notes in Computer Science, Proc. Geosensor Networks, 5659, 131-137. ^ http://www.libelium.com/wireless_sensor_networks_to_detec_forest_fires/ ^ Air Quality Monitoring ^ Ma, Y.; Richards, M.; Ghanem, M.; Guo, Y.; Hassard, J. (2008). "Air Pollution Monitoring and Mining Based on Sensor Grid in London". Sensors 8 (6): 3601. doi:10.3390/s8063601. edit ^ J.D. Kenney, D.R. Poole, G.C. Willden, B.A. Abbott, A.P. Morris, R.N. McGinnis, and D.A. Ferrill, "Precise Positioning with Wireless Sensor Nodes: Monitoring Natural Hazards in All Terrains", 2009 IEEE International Conference on Systems, Man, and Cybernetics, San Antonio, TX, USA, Oct. 2009. ^ T.L. Dinh, W. Hu, P. Sikka, P. Corke, L. Overs and S. Brosnan, "Design and Deployment of a Remote Robust Sensor Network: Experiences from an Outdoor Water Quality Monitoring Network", 2007 32nd IEEE Conference on Local Computer Networks ^ Anastasi et al.A Comprehensive Analysis of the MAC Unreliability Problem in IEEE 802.15.4 Wireless Sensor Networks , DOI 10.1109/TII.2010.2085440. ^ R. Matischek: Real-Time Communication MAC Protocols for Wireless Sensor Networks, 2012, ISBN 978-3-8300-6349-0. ^ Water Monitoring ^ Agriculture Monitoring ^ F. Viani, P. Rocca, M. Benedetti, G. Oliveri, A. Massa , "Electromagnetic passive localization and tracking of moving targets in a WSN-infrastructured environment " in Inverse Problems, vol. 26, (2010), p. 1-15. - DOI: 10.1088/02665611/26/7/074003 ^ Debnath, Ashmita; Singaravelu, Pradheepkumar; Verma, Shekhar (19 December 2012). "Efficient spatial privacy preserving scheme for sensor network". Central European Journal of Engineering 3 (1): 1–10. doi:10.2478/s13531-012-0048-7. ^ Surie, D., Laguionie, O., Pederson, T.: "Wireless Sensor Networking of Everyday Objects in a Smart Home Environment". In Proceedings of the 4th International Conference on Intelligent Sensors, Sensor Networks and Information Processing, Sydney, Australia, pp. 189-194, (2008)

6.

7. 8.
9.

10.

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12. 13. 14. 15. 16.

17.

18.

19. 20.

^ TinyOS Programming, Philip Levis, Cambridge University Press, 2009 ^ Oliver Hahm, Emmanuel Baccelli, Mesut Günes, Matthias Wählisch, Thomas C. Schmidt, RIOT OS: Towards an OS for the Internet of Things, In: Proc. of the 32nd IEEE INFOCOM. Poster Session, Piscataway, NJ, USA:IEEE Press, 2013. ^ Silva, D.; Ghanem, M.; Guo, Y. (2012). "WikiSensing: An Online Collaborative Approach for Sensor Data Management". Sensors 12 (12): 13295. doi:10.3390/s121013295. edit ^ Muaz Niazi, Amir Hussain (2011). A Novel Agent-Based Simulation Framework for Sensing in Complex Adaptive Environments. IEEE Sensors Journal, Vol.11 No. 2, 404–412. Paper

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22.

External links


IEEE 802.15.4 Standardization Committee [hide]
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Wireless Sensor Network
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Contiki ERIKA Enterprise Nano-RK TinyOS LiteOS OpenTag NanoQplus ANT 6LoWPAN DASH7 ONE-NET

Operating systems

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Industry standards

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ZigBee Z-Wave Wibree WirelessHART 802.15.4 MiWi C LabVIEW nesC Iris Mote Sun SPOT Xbee Arduino TinyDB TOSSIM NS-2 OPNET NetSim LinuxMCE Key distribution Location estimation Sensor Web Telemetry AODV

Programming languages

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Hardware

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Software

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Applications

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Protocols



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DSR TSMP SenSys IPSN EWSN

Conferences/Journals

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Categories: • Wireless sensor network • Wireless networking

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Wireless ad hoc network
From Wikipedia, the free encyclopedia Jump to: navigation, search

A wireless ad hoc network is a decentralized type of wireless network.[1] The network is ad hoc because it does not rely on a pre existing infrastructure, such as routers in wired networks or access points in managed (infrastructure) wireless networks. Instead, each node participates in routing by forwarding data for other nodes, so the determination of which nodes forward data is made dynamically on the basis of network connectivity. In addition to the classic routing, ad hoc networks can use flooding for forwarding the data. An ad hoc network typically refers to any set of networks where all devices have equal status on a network and are free to associate with any other ad hoc network device in link range. Ad hoc network often refers to a mode of operation of IEEE 802.11 wireless networks. It also refers to a network device's ability to maintain link status information for any number of devices in a 1-link (aka "hop") range, and thus, this is most often a Layer 2 activity. Because this is only a Layer 2 activity, ad hoc networks alone may not support a routeable IP network environment without additional Layer 2 or Layer 3 capabilities. The earliest wireless ad hoc networks were the "packet radio" (PRNETs) from the 1970s, sponsored by DARPA after the ALOHAnet project.

Contents
• • • • • •

1 Application 2 Technical requirements 3 Medium-access control 4 Simulation of wireless ad hoc networks 5 See also 6 References

Application
The decentralized nature of wireless ad hoc networks makes them suitable for a variety of applications where central nodes can't be relied on and may improve the scalability of networks compared to wireless managed networks, though theoretical[2] and practical[3] limits to the overall capacity of such networks have been identified. Minimal configuration and quick deployment make ad hoc networks suitable for emergency situations like natural disasters or military conflicts. The presence of dynamic and adaptive routing protocols enables ad hoc networks to be formed quickly. Wireless ad hoc networks can be further classified by their application:


mobile ad hoc networks (MANET)

Technical requirements
An ad hoc network is made up of multiple “nodes” connected by “links.” Links are influenced by the node's resources (e.g., transmitter power, computing power and memory) and behavioral properties (e.g., reliability), as well as link properties (e.g. length-oflink and signal loss, interference and noise). Since links can be connected or disconnected at any time, a functioning network must be able to cope with this dynamic restructuring, preferably in a way that is timely, efficient, reliable, robust, and scalable. The network must allow any two nodes to communicate by relaying the information via other nodes. A “path” is a series of links that connects two nodes. Various routing methods use one or two paths between any two nodes; flooding methods use all or most of the available paths.[4]

Medium-access control
In most wireless ad hoc networks, the nodes compete for access to shared wireless medium, often resulting in collisions (interference). Using cooperative wireless communications improves immunity to interference by having the destination node combine self-interference and othernode interference to improve decoding of the desired signal.

Simulation of wireless ad hoc networks
One key problem in Wireless Ad Hoc networks is foreseeing the variety of possible situations that can occur. As a result, Modeling and Simulation using extensive parameter sweeping and what-if analysis becomes an extremely important paradigm for use in ad hoc networks. Traditional M&S tools include NS2,(and recently NS3), OPNET Modeler, and NetSim.

However, these tools focus primarily on the simulation of the entire protocol stack of the system. Although this can be important in the proof-of-concept implementations of systems, the need for a more advanced simulation methodology is always there. Agent-based modeling and simulation offers such a paradigm. Not to be confused with multi-agent systems and intelligent agents, agent-based modeling[5] originated from social sciences, where the goal was to evaluate and view large-scale systems with numerous interacting "AGENT" or components in a wide variety of random situations to observe global phenomena. Unlike traditional AI systems with Intelligent agents, agent-based modeling is similar to the real world. Agent-based models are thus effective in modeling bio-inspired and nature-inspired systems. In these systems, the basic interactions of the components the system, also called Complex Adaptive System, are simple but result in advanced global phenomena such as emergence.

See also
• • • • •

802.11 Mobile ad hoc network (MANET) List of ad hoc routing protocols Wi-Fi Direct Independent Basic Service Set (IBSS)

References
1. ^ Chai Keong Toh, Ad Hoc Mobile Wireless Networks, Prentice Hall Publishers , 2002. 2. ^ P. Gupta and P.R. Kumar. Capacity of wireless networks. IEEE Transactions on Information Theory, Volume 46, Issue 2, March 2000, doi:10.1109/18.825799 3. ^ Jinyang Li, Charles Blake, Douglas S. J. De Couto, Hu Imm Lee, and Robert Morris, Capacity of Ad Hoc Wireless Networks, in the proceedings of the 7th ACM International Conference on Mobile Computing and Networking, Rome, Italy, July 2001 4. ^ Wu S.L., Tseng Y.C., "Wireless Ad Hoc Networking, Auerbach Publications", 2007 ISBN 978-0-8493-9254-2 5. ^ Muaz Niazi, Amir Hussain, Agent based Tools for Modeling and Simulation of Self-Organization in Peer-to-Peer, Ad Hoc and other Complex Networks, Feature Issue, IEEE Communications Magazine, Vol.47 No.3, March 2009, pp 163–173.Paper Categories: • Wireless networking

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Wireless network
From Wikipedia, the free encyclopedia Jump to: navigation, search

Wireless icon.

Wireless network refers to any type of computer network that utilizes some form of wireless network connection. It is a method by which homes, telecommunications networks and enterprise (business) installations avoid the costly process of introducing cables into a building, or as a connection between various equipment locations.[1] Wireless telecommunications networks are generally implemented and administered using radio communication. This implementation takes place at the physical level (layer) of the OSI model network structure.[2]

Contents


1 Types of wireless networks o 1.1 Wireless PAN
o o o o o

1.2 Wireless LAN 1.3 Wireless mesh network 1.4 Wireless MAN 1.5 Wireless WAN 1.6 Cellular network

• •

2 Uses 3 Properties
o o

3.1 General 3.2 Performance

o o o o

3.3 Space 3.4 Home 3.5 Wireless Network Elements 3.6 Capacity
 

3.6.1 Link 3.6.2 Network

• • • • •

4 Environmental concerns 5 See also 6 References 7 Further reading 8 External links

Types of wireless networks
Wireless PAN
Wireless personal area networks (WPANs) interconnect devices within a relatively small area, that is generally within a person's reach.[3] For example, both Bluetooth radio and invisible infrared light provides a WPAN for interconnecting a headset to a laptop. ZigBee also supports WPAN applications.[4] Wi-Fi PANs are becoming commonplace (2010) as equipment designers start to integrate Wi-Fi into a variety of consumer electronic devices. Intel "My WiFi" and Windows 7 "virtual Wi-Fi" capabilities have made Wi-Fi PANs simpler and easier to set up and configure.[5]

Wireless LAN
Main article: Wireless LAN

A wireless local area network (WLAN) links two or more devices over a short distance using a wireless distribution method, usually providing a connection through an access point for Internet access. The use of spread-spectrum or OFDM technologies may allow users to move around within a local coverage area, and still remain connected to the network. Products using the IEEE 802.11 WLAN standards are marketed under the Wi-Fi brand name. Fixed wireless technology implements point-to-point links between computers or networks at two distant locations, often using dedicated microwave or modulated laser light beams over line of sight paths. It is often used in cities to connect networks in two or more buildings without installing a wired link.

Wireless mesh network
Main article: wireless mesh network

A wireless mesh network is a wireless network made up of radio nodes organized in a mesh topology. Each node forwards messages on behalf of the other nodes. Mesh networks can "self heal", automatically re-routing around a node that has lost power.

Wireless MAN
Wireless metropolitan area networks are a type of wireless network that connects several wireless LANs.


WiMAX is a type of Wireless MAN and is described by the IEEE 802.16 standard.[6]

Wireless WAN
Wireless wide area networks are wireless networks that typically cover large areas, such as between neighboring towns and cities, or city and suburb. These networks can be used to connect branch offices of business or as a public internet access system. The wireless connections between access points are usually point to point microwave links using parabolic dishes on the 2.4 GHz band, rather than omnidirectional antennas used with smaller networks. A typical system contains base station gateways, access points and wireless bridging relays. Other configurations are mesh systems where each access point acts as a relay also. When combined with renewable energy systems such as photo-voltaic solar panels or wind systems they can be stand alone systems.

Cellular network
Main article: cellular network

Top of a cellular radio tower

A cellular network or mobile network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver, known as a cell site or base station. In a cellular network, each cell characteristically uses a different set of radio frequencies from all their immediate neighbouring cells to avoid any interference. When joined together these cells provide radio coverage over a wide geographic area. This enables a large number of portable transceivers (e.g., mobile phones, pagers, etc.) to communicate with each other and with fixed transceivers and telephones anywhere in the network, via base stations, even if some of the transceivers are moving through more than one cell during transmission. Although originally intended for cell phones, with the development of smartphones, cellular telephone networks routinely carry data in addition to telephone conversations:




Global System for Mobile Communications (GSM): The GSM network is divided into three major systems: the switching system, the base station system, and the operation and support system. The cell phone connects to the base system station which then connects to the operation and support station; it then connects to the switching station where the call is transferred to where it needs to go. GSM is the most common standard and is used for a majority of cell phones.[7] Personal Communications Service (PCS): PCS is a radio band that can be used by mobile phones in North America and South Asia. Sprint happened to be the first service to set up a PCS. D-AMPS: Digital Advanced Mobile Phone Service, an upgraded version of AMPS, is being phased out due to advancement in technology. The newer GSM networks are replacing the older system.



Uses
Some examples of usage include cellular phones which are part of everyday wireless networks, allowing easy personal communications. Another example, Inter-continental network systems, use radio satellites to communicate across the world. Emergency services such as the police utilize wireless networks to communicate effectively as well. Individuals and businesses use wireless networks to send and share data rapidly, whether it be in a small office building or across the world.

Properties
General
In a general sense, wireless networks offer a vast variety of uses by both business and home users.[8]

"Now, the industry accepts a handful of different wireless technologies. Each wireless technology is defined by a standard that describes unique functions at both the Physical and the Data Link layers of the OSI Model. These standards differ in their specified signaling methods, geographic ranges, and frequency usages, among other things. Such differences can make certain technologies better suited to home networks and others better suited to network larger organizations."[8]

Performance
Each standard varies in geographical range, thus making one standard more ideal than the next depending on what it is one is trying to accomplish with a wireless network.[8] The performance of wireless networks satisfies a variety of applications such as voice and video. The use of this technology also gives room for expansions, such as from 2G to 3G and, most recently, 4G technology, which stands for fourth generation of cell phone mobile communications standards. As wireless networking has become commonplace, sophistication increases through configuration of network hardware and software, and greater capacity to send and receive larger amounts of data, faster, is achieved.[9]

Space
Space is another characteristic of wireless networking. Wireless networks offer many advantages when it comes to difficult-to-wire areas trying to communicate such as across a street or river, a warehouse on the other side of the premise or buildings that are physically separated but operate as one.[9] Wireless networks allow for users to designate a certain space which the network will be able to communicate with other devices through that network. Space is also created in homes as a result of eliminating clutters of wiring.[10] This technology allows for an alternative to installing physical network mediums such as TPs, coaxes, or fiber-optics, which can also be expensive.

Home
For homeowners, wireless technology is an effective option compared to ethernet for sharing printers, scanners, and high speed internet connections. WLANs help save the cost of installation of cable mediums, save time from physical installation, and also creates mobility for devices connected to the network.[10] Wireless networks are simple and require as few as one single wireless access point connected directly to the Internet via a router.[8]

Wireless Network Elements
The telecommunications network at the physical layer also consists of many interconnected wireline Network Elements (NEs). These NEs can be stand-alone systems or products that are either supplied by a single manufacturer, or are assembled by the service provider (user) or system integrator with parts from several different manufacturers. Wireless NEs are products and devices used by a wireless carrier to provide support for the backhaul network as well as a Mobile Switching Center (MSC).

Reliable wireless service depends on the network elements at the physical layer to be protected against all operational environments and applications (see GR-3171, Generic Requirements for Network Elements Used in Wireless Networks - Physical Layer Criteria).[11] What are especially important are the NEs that are located on the cell tower to the Base Station (BS) cabinet. The attachment hardware and the positioning of the antenna and associated closures/cables are required to have adequate strength, robustness, corrosion resistance, and rain/solar resistance for expected wind, storm, ice, and other weather conditions. Requirements for individual components, such as hardware, cables, connectors, and closures, shall take into consideration the structure to which they are attached.

Capacity
Link The maximum data rate of any single wireless link can be described by the Shannon's theorem which is related to the bandwidth in hertz, and the noise on the channel. Network
This section requires expansion.
(April 2013)

The total network bandwidth depends on how dispersive the medium is (more dispersive medium generally has better total bandwidth because it minimises interference), how many frequencies are available, how noisy those frequencies are, whether directional antenna are in use, whether nodes employ power control and so on.

Environmental concerns
See also: Wireless electronic devices and health

Wireless access points are also often close to humans, but the drop off in power over distance is fast, following the inverse-square law.[12] The position of the United Kingdom's Health Protection Agency (HPA) is that “...radio frequency (RF) exposures from WiFi are likely to be lower than those from mobile phones.” It also saw “...no reason why schools and others should not use WiFi equipment.”[13] In October 2007, the HPA launched a new “systematic” study into the effects of WiFi networks on behalf of the UK government, in order to calm fears that had appeared in the media in a recent period up to that time".[14] Dr Michael Clark, of the HPA, says published research on mobile phones and masts does not add up to an indictment of WiFi.[15]

See also


Exposed terminal problem

• • • • •

Physical layer Wireless community network Wireless access point Wireless LAN client comparison Wireless site survey

References
1. ^ "Overview of Wireless Communications". cambridge.org. Retrieved 2008-02-08. 2. ^ "Getting to Know Wireless Networks and Technology". informit.com. Retrieved 2008-02-08. 3. 4. 5. 6. 7. 2011. 8. 9. 10. 11. 12. ^ a b c d Dean Tamara (2010). Network+ Guide to Networks (5th ed.). Boston: Cengage Learning. ISBN 978-1-4239-0245-4. ^ a b "Wireless LAN Technologies". Source Daddy web site. Retrieved 29 August 2011. ^ a b "WLAN Benefits". Wireless Center commercial web site. Retrieved 29 August 2011. ^ GR-3171-CORE,Generic Requirements for Network Elements Used in Wireless Networks - Physical Layer Criteria ^ Foster, Kenneth R (March 2007). "Radiofrequency exposure from wireless LANs utilizing Wi-Fi technology". Health Physics 92 (3): 280–289. doi:10.1097/01.HP.0000248117.74843.34. PMID 17293700. ^ "WiFi". Health Protection Agency. 2009-10-26. Retrieved 2009-12-27. ^ "Health Protection Agency announces further research into use of WiFi". Health Protection Agency. Retrieved 2008-08-28. ^ Daniels, Nicki (2006-12-11). "Wi-fi: should we be worried?". The Times (London). Retrieved 2007-09-16. "All the expert reviews done here and ^ "Wireless Networks: Bluetooth To Mobile Phones". ^ "Wireless Network Industry Report". Retrieved 2008-07-08. ^ "Wi-Fi Personal Area Networks get a boost with Windows 7 and Intel My WiFi". Retrieved 2010-04-27. ^ "Facts About WiMAX And Why Is It "The Future of Wireless Broadband"". ^ "GSM World statistics". GSM Association. 2010. Retrieved 16 March

13. 14. 15.

abroad indicate that there is unlikely to be a health risk from wireless networks. … When we have conducted measurements in schools, typical exposures from WiFi are around 20 millionths of the international guideline levels of exposure to radiation. As a comparison, a child on a mobile phone receives up to 50 per cent of guideline levels. So a year sitting in a classroom near a wireless network is roughly equivalent to 20 minutes on a mobile. If WiFi should be taken out of schools, then the mobile phone network should be shut down, too—and FM radio and TV, as the strength of their signals is similar to that from WiFi in classrooms...."

Further reading


• • • • • • • • • •

Wireless Networking in the Developing World: A practical guide to planning and building low-cost telecommunications infrastructure (2nd ed.). Hacker Friendly LLC. 2007. p. 425. Pahlavan, Kaveh; Levesque, Allen H (1995). Wireless Information Networks. John Wiley & Sons. ISBN 0-471-10607-0. Geier, Jim (2001). Wireless LANs. Sams;. ISBN 0-672-32058-4. Goldsmith, Andrea (2005). Wireless Communications. Cambridge University Press. ISBN 0-521-83716-2. Molisch, Andreas (2005). Wireless Communications. Wiley-IEEE Press. ISBN 0470-84888-X. Pahlavan, Kaveh; Krishnamurthy, Prashant (2002). Principles of Wireless Networks – a Unified Approach . Prentice Hall. ISBN 0-13-093003-2. Rappaport, Theodore (2002). Wireless Communications: Principles and Practice. Prentice Hall. ISBN 0-13-042232-0. Rhoton, John (2001). The Wireless Internet Explained. Digital Press. ISBN 155558-257-5. Tse, David; Viswanath, Pramod (2005). Fundamentals of Wireless Communication. Cambridge University Press. ISBN 0-521-84527-0. Kostas Pentikousis (March 2005). "Wireless Data Networks". Internet Protocol Journal 8 (1). Retrieved 29 August 2011. Pahlavan, Kaveh; Krishnamurthy, Prashant (2009). Networking Fundamentals – Wide, Local and Personal Area Communications . Wiley. ISBN 978-0-47099290-6.

External links


Wireless at the Open Directory Project [show]

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Wireless mesh network
From Wikipedia, the free encyclopedia Jump to: navigation, search

Animation showing self healing wireless mesh (Click to enlarge)

A wireless mesh network (WMN) is a communications network made up of radio nodes organized in a mesh topology. Wireless mesh networks often consist of mesh clients, mesh routers and gateways. The mesh clients are often laptops, cell phones and other wireless devices while the mesh routers forward traffic to and from the gateways which may, but need not, connect to the Internet. The coverage area of the radio nodes working as a single network is sometimes called a mesh cloud. Access to this mesh cloud is dependent on the radio nodes working in harmony with each other to create a radio network. A mesh network is reliable and offers redundancy. When one node can no longer operate, the rest of the nodes can still communicate with each other, directly or through one or more intermediate nodes. The animation below illustrates how wireless mesh networks can self form and self heal. Wireless mesh networks can be implemented with various wireless technology including 802.11, 802.15, 802.16, cellular technologies or combinations of more than one type.

Contents


1 History o 1.1 Network structure

o o o o o o •

1.2 Architecture 1.3 Management 1.4 Applications 1.5 Operation 1.6 Multi-radio mesh 1.7 Research topics

2 Protocols
o o

2.1 Routing protocols 2.2 Autoconfiguration protocols

• • •

3 See also 4 References 5 External links

History
Main article: History of wireless mesh networking

Network structure Architecture
Wireless mesh architecture is a first step towards providing cost effective and dynamic highbandwidth networks over a specific coverage area. Wireless mesh architectures infrastructure is, in effect, a router network minus the cabling between nodes. It's built of peer radio devices that don't have to be cabled to a wired port like traditional WLAN access points (AP) do. Mesh architecture sustains signal strength by breaking long distances into a series of shorter hops. Intermediate nodes not only boost the signal, but cooperatively make forwarding decisions based on their knowledge of the network, i.e. perform routing. Such an architecture may with careful design provide high bandwidth, spectral efficiency, and economic advantage over the coverage area. Wireless mesh networks have a relatively stable topology except for the occasional failure of nodes or addition of new nodes. The path of traffic, being aggregated from a large number of end users, changes infrequently. Practically all the traffic in an infrastructure mesh network is either forwarded to or from a gateway, while in ad hoc networks or client mesh networks the traffic flows between arbitrary pairs of nodes.[1]

Management

This type of infrastructure can be decentralized (with no central server) or centrally managed (with a central server),[2] both are relatively inexpensive, and very reliable and resilient, as each node needs only transmit as far as the next node. Nodes act as routers to transmit data from nearby nodes to peers that are too far away to reach in a single hop, resulting in a network that can span larger distances. The topology of a mesh network is also reliable, as each node is connected to several other nodes. If one node drops out of the network, due to hardware failure or any other reason, its neighbors can quickly find another route using a routing protocol.

Applications
Mesh networks may involve either fixed or mobile devices. The solutions are as diverse as communication needs, for example in difficult environments such as emergency situations, tunnels, oil rigs, battlefield surveillance, high speed mobile video applications on board public transport or real time racing car telemetry. An important possible application for wireless mesh networks is VoIP. By using a Quality of Service scheme, the wireless mesh may support local telephone calls to be routed through the mesh. Some current applications:
• •

U.S. military forces are now using wireless mesh networking to connect their computers, mainly ruggedized laptops, in field operations. Electric meters now being deployed on residences transfer their readings from one to another and eventually to the central office for billing without the need for human meter readers or the need to connect the meters with cables.[3] The laptops in the One Laptop per Child program use wireless mesh networking to enable students to exchange files and get on the Internet even though they lack wired or cell phone or other physical connections in their area. The 66-satellite Iridium constellation operates as a mesh network, with wireless links between adjacent satellites. Calls between two satellite phones are routed through the mesh, from one satellite to another across the constellation, without having to go through an earth station. This makes for a smaller travel distance for the signal, reducing latency, and also allows for the constellation to operate with far fewer earth stations that would be required for 66 traditional communications satellites.





Operation
The principle is similar to the way packets travel around the wired Internet— data will hop from one device to another until it reaches its destination. Dynamic routing algorithms implemented in each device allow this to happen. To implement such dynamic routing protocols, each device needs to communicate routing information to other devices in the network. Each device then determines what to do with the data it receives — either pass it on to the next device or keep it, depending on the protocol. The routing algorithm used should attempt to always ensure that the data takes the most appropriate (fastest) route to its destination.

Multi-radio mesh
Multi-radio mesh refers to a unique pair of dedicated radios on each end of the link. This means there is a unique frequency used for each wireless hop and thus a dedicated CSMA collision domain. This is a true mesh link where you can achieve maximum performance without bandwidth degradation in the mesh and without adding latency. Thus voice and video applications work just as they would on a wired Ethernet network. In true 802.11 networks, there is no concept of a mesh. There are only Access Points (AP's) and Stations. A multi-radio wireless mesh node will dedicate one of the radios to act as a station, and connect to a neighbor node AP radio.

Research topics
One of the more often cited papers on Wireless Mesh Networks identified the following areas as open research problems in 2005


New modulation scheme o In order to achieve higher transmission rate, new wideband transmission schemes other than OFDM and UWB are needed. Advanced antenna processing
o



Advanced antenna processing including directional, smart and multiple antenna technologies is further investigated, since their complexity and cost are still too high for wide commercialization.



Flexible spectrum management
o

Tremendous efforts on research of frequency-agile techniques are being performed for increased efficiency.



Cross-layer optimization
o

Cross-layer research is a popular current research topic where information is shared between different communications layers in order to increase the knowledge and current state of the network. This could enable new and more efficient protocols to be developed. A joint protocol which combines various design problems like routing, scheduling, channel assignment etc. can achieve higher performance since it is proven that these problems are strongly co-related. [4] It is important to note that careless cross-layer design could lead to code which is difficult to maintain and extend. [5]

Protocols
Routing protocols

There are more than 70 competing schemes for routing packets across mesh networks. Some of these include:
• • • • • • • • • • • • • • • •

AODV (Ad hoc On-Demand Distance Vector) B.A.T.M.A.N. (Better Approach To Mobile Adhoc Networking) Babel (protocol) (a distance-vector routing protocol for IPv6 and IPv4 with fast convergence properties) DNVR (Dynamic NIx-Vector Routing) DSDV (Destination-Sequenced Distance-Vector Routing) DSR (Dynamic Source Routing) HSLS (Hazy-Sighted Link State) HWMP (Hybrid Wireless Mesh Protocol) IWMP (Infrastructure Wireless Mesh Protocol) for Infrastructure Mesh Networks by GRECO UFPB-Brazil MRP (Wireless mesh networks routing protocol) by Jangeun Jun and Mihail L. Sichitiu OLSR (Optimized Link State Routing protocol) OORP (OrderOne Routing Protocol) (OrderOne Networks Routing Protocol) OSPF (Open Shortest Path First Routing) PWRP (Predictive Wireless Routing Protocol) TORA (Temporally-Ordered Routing Algorithm) ZRP (Zone Routing Protocol)

The IEEE is developing a set of standards under the title 802.11s to define an architecture and protocol for ESS Mesh Networking. A more thorough list can be found at Ad hoc routing protocol list.

Autoconfiguration protocols
Wikimedia Commons has media related to: Mesh network

Standard autoconfiguration protocols, such as DHCP or IPv6 stateless autoconfiguration may be used over mesh networks.

Mesh network specific autoconfiguration protocols include:
• • •

Ad Hoc Configuration Protocol (AHCP) Proactive Autoconfiguration (Proactive Autoconfiguration Protocol) Dynamic WMN Configuration Protocol (DWCP)

See also
• • •

Ant colony optimization Cjdns Comparison of wireless data standards CUWiN DASH7 Firetide IEEE 802.11s INSTEON MeshBox

• • • • • • • • •

Mobile ad hoc network Netsukuku Optimized Link State Routing protocol Peer-to-peer Public Safety Network Roofnet Senceive Shared mesh Smart antenna

• • • • • •

Software-defined radio Switched mesh TinyOS Wireless ad hoc network Wireless community network Wireless Distribution System (WDS) Wireless LAN (WLAN) ZigBee Village telco

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References
1. ^ J. Jun, M.L. Sichitiu, "The nominal capacity of wireless mesh networks", in IEEE Wireless Communications, vol 10, 5 pp 8-14. October 2003 2. ^ S.M. Chen, P, Lin, D-W Huang, S-R Yang, "A study on distributed/centralized scheduling for wireless mesh network" in Proceedings of the 2006 International Conference on Wireless Communications and Mobile Computing, pp 599 - 604. Vancouver, British Columbia, Canada. 2006 3. ^ ZigBee.org Smart Energy Overview. 4. ^ Pathak, P. H.; Dutta, R. (2011). "A Survey of Network Design Problems and Joint Design Approaches in Wireless Mesh Networks". IEEE Communications Surveys & Tutorials 13 (3): 396–428. doi:10.1109/SURV.2011.060710.00062. 5. ^ V. Kawadia, P. R. Kumar (February 2005). A Cautionary Perspective on Cross-Layer Design in IEEE Wireless Communications . pp. 3–11.

External links
• • • • • • • •

Wireless LAN Mesh Whitepaper How Wireless Mesh Networks Work at HowStuffWorks First, Second and Third Generation Mesh Architectures History and evolution of Mesh Networking Architectures Miners Give a Nod to Nodes Article reprint from Mission Critical Magazine on Mesh in underground mining IET From hotspots to blankets Ian. F. Akyildiz and Xudong Wang, "A Survey on Wireless Mesh Networks," IEEE Communications Magazine, vol. 43, no. 9, s23-s30, Sept. 2005 Mesh Networks Research Group Projects and tutorials' compilation related to the Wireless Mesh Networks Linux Wireless Subsystem (80211) by Rami Rosen

Categories: • Wireless networking • Open problems

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Dansk Deutsch Español ‫فارسی‬ 한국어 Suomi 日日 Edit links This page was last modified on 15 July 2013 at 15:59. Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. Privacy policy About Wikipedia Disclaimers Contact Wikipedia

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Mobile ad hoc network
From Wikipedia, the free encyclopedia Jump to: navigation, search

A mobile ad hoc network (MANET) is a self-configuring infrastructureless network of mobile devices connected by wireless. Ad hoc is Latin and means "for this purpose".[1] Each device in a MANET is free to move independently in any direction, and will therefore change its links to other devices frequently. Each must forward traffic unrelated to its own use, and therefore be a router. The primary challenge in building a MANET is equipping each device to continuously maintain the information required to properly route traffic. Such networks may operate by themselves or may be connected to the larger Internet. MANETs are a kind of Wireless ad hoc network that usually has a routable networking environment on top of a Link Layer ad hoc network. The growth of laptops and 802.11/Wi-Fi wireless networking have made MANETs a popular research topic since the mid-1990s. Many academic papers evaluate protocols and their abilities, assuming varying degrees of mobility within a bounded space, usually with all nodes within a few hops of each other. Different protocols are then evaluated based on measures such as the packet drop rate, the overhead introduced by the routing protocol, end-to-end packet delays, network throughput etc.

Contents
• • • • •

1 Types of MANET 2 Simulation of MANETs 3 Data Monitoring and Mining Using MANETs 4 Security of MANETs 5 Classification of Attacks on MANETs

• • • •

6 See also 7 References 8 Further reading 9 External links

Types of MANET


Vehicular Ad hoc Networks (VANETs) are used for communication among vehicles and between vehicles and roadside equipment Internet based mobile ad hoc networks (iMANET) are ad hoc networks that link mobile nodes and fixed Internet-gateway nodes. In such type of networks normal adhoc routing algorithms don't apply directly.





Intelligent vehicular ad hoc networks (InVANETs) are a kind of artificial intelligence that helps vehicles to behave in intelligent manners during vehicle-to-vehicle collisions, accidents, drunken driving etc.

Simulation of MANETs
There are several ways to study MANETs. One solution is the use of simulation tools like OPNET, NetSim and NS2

Data Monitoring and Mining Using MANETs
MANETS can be used for facilitating the collection of sensor data for data mining for a variety of applications such as air pollution monitoring and different types of architectures can be used for such applications.[2] It should be noted that a key characteristic of such applications is that nearby sensor nodes monitoring an environmental feature typically register similar values. This kind of data redundancy due to the spatial correlation between sensor observations inspires the techniques for in-network data aggregation and mining. By measuring the spatial correlation between data sampled by different sensors, a wide class of specialized algorithms can be developed to develop more efficient spatial data mining algorithms as well as more efficient routing strategies.[3] Also researchers have developed performance models[4][5] for MANET by applying Queueing Theory.

Security of MANETs
A lot of research was done in the past but the most significant contributions were the PGP (Pretty Good Privacy) and the trust based security but none of the protocols made a decent trade off between security and performance. In an attempt to enhance security in MANETs many

researchers have suggested and implemented new improvements to the protocols and some of them have suggested new protocols.

Classification of Attacks on MANETs
These attacks on MANETs challenge the mobile infrastructure in which nodes can join and leave easily with dynamics requests without a static path of routing. Schematics of various attacks as described by Al-Shakib Khan [1] on individual layer are as under:
• • • • •

Application Layer: Malicious code, Repudiation Transport Layer: Session hijacking, Flooding Network Layer: Sybil, Flooding, Black Hole, Grey Hole. Worm Hole, Link Spoofing, Link Withholding, Location disclosure etc. Data Link/MAC: Malicious Behavior, Selfish Behavior, Active, Passive, Internal External Physical: Interference, Traffic Jamming, Eavesdropping

See also
• • • • • • • •

AmbientTalk, an experimental programming language for MANETs List of ad hoc routing protocols Delay-tolerant networking Wireless community network Wireless mesh network Backpressure Routing Data Mining Wireless Sensor Networks

References
1. ^ Tomas Krag and Sebastian Büettrich (2004-01-24). "Wireless Mesh Networking". O'Reilly Wireless Dev Center. Retrieved 2009-01-20. 2. ^ Ma, Y.; Richards, M.; Ghanem, M.; Guo, Y.; Hassard, J. (2008). "Air Pollution Monitoring and Mining Based on Sensor Grid in London". Sensors 8 (6): 3601. doi:10.3390/s8063601. edit 3. ^ Ma, Y.; Guo, Y.; Tian, X.; Ghanem, M. (2011). "Distributed Clustering-Based Aggregation Algorithm for Spatial Correlated Sensor Networks". IEEE Sensors Journal 11 (3): 641. doi:10.1109/JSEN.2010.2056916. edit

4. ^ Kleinrock, Leonard (1975). "Packet Switching in Radio Channels: Part I-Carrier Sense Multiple-Access Modes and Their Throughput-Delay Characteristics". 5. ^ Shi, Zhefu; Beard, Cory; Mitchell, Ken (2008). "Tunable traffic control for multihop CSMA networks".

Further reading
Mobile ad hoc social network (Overview):
• •

Abdul Shabbir, Anasuri Sunil Kumar (January 2012). "An Efficient Authentication Protocol for Security in MANETs". IJCCT 3 (1): 71–74. Kahn, R. E. (January 1977). "The Organization of Computer Resources into a Packet Radio Network". IEEE Transactions on Communications. COM-25 (1): 169–178. Jubin, J., and Tornow, J. D. (January 1987). "The DARPA Packet Radio Network Protocols". Proceedings of the IEEE 75 (1). N. Schacham and J. Westcott (January 1987). "Future directions in packet radio architectures and protocols". Proceedings of the IEEE 75 (1): 83–99. doi:10.1109/PROC.1987.13707.

• •

Ad Hoc Network Papers (Overview):


Royer, E., Chai Keong Toh (April 1999). "A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks". IEEE Personal Communications 6 (2): 46–55. doi:10.1109/98.760423. Mauve, M., Widmer, J., Hartenstein, H. (December 2001). "A Survey on Position-Based Routing in Mobile Ad Hoc Networks". IEEE Network 1 (6): 30– 39. doi:10.1109/65.967595. D. Djenouri, L. Kheladi, N. Badache. (4th quarter 2005). "A Survey of Security Issues in Mobile Ad hoc and Sensor Networks". IEEE Communications Surveys and Tutorials 7 (4). Maihöfer, C. (2nd quarter 2004). "A Survey on Geocast Routing Protocols". IEEE Communications Surveys and Tutorials 6 (2).







External links
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IETF MANET group NIST MANET and Sensor Network Security project Wireless Ad Hoc Networks Bibliography Hybrid Ad Hoc Mesh Networks in Military

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IEEE Intelligent Transportation Systems Society – for VANETs Smart Multi-Grid Wifi Mesh: Integrated wifi mesh network provides metering, traffic safety, wifi access to communities in US. [hide]
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Channel access methods and Media access control (MAC)/Multiple-access protocols

FDM A

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OFDMA WDMA SC-FDMA MF-TDMA STDMA W-CDMA TD-CDMA TD-SCDMA DS-CDMA FH-CDMA OFHMA MC-CDMA

TDM A

Chann el based



CDM A

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SDM A



HC-SDMA

PDM A

PAM A

Collisio n recover y

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ALOHA Slotted ALOHA R-ALOHA MACA MACAW CSMA CSMA/CD CSMA/CA DCF PCF HCF CSMA/CARP Token ring Token bus MS-ALOHA

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Collisio n avoida nce Packet based

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Collisio n free

Delay & disrupt ion toleran t

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DTN Mobile Ad-Hoc Dynamic Source Routing

Duplex ing metho ds

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TDD FDD

Categories: • Channel access methods • Wireless networking


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ALOHA - What is ALOHA?
Category: Communication Networks

ALOHA: ALOHA is a system for coordinating and arbitrating access to a shared communication Networks channel. It was developed in the 1970s by Norman Abramson and his colleagues at the University of Hawaii. The original system used for ground based radio broadcasting, but the system has been implemented in satellite communication systems. A shared communication system like ALOHA requires a method of handling collisions that occur when two or more systems attempt to transmit on the channel at the same time. In the ALOHA system, a node transmits whenever data is available to send. If another node transmits at the same time, a collision occurs, and the frames that were transmitted are lost. However, a node can listen to broadcasts on the medium, even its own, and determine whether the frames were transmitted.

Aloha means "Hello". Aloha is a multiple access protocol at the datalink layer and proposes how multiple terminals access the medium without interference or collision. In 1972 Roberts developed a protocol that would increase the capacity of aloha two fold. The Slotted Aloha protocol involves dividing the time interval into discrete slots and each slot interval corresponds to the time period of one frame. This method requires synchronization between the sending nodes to prevent collisions.

There are two different versior.s/types of ALOHA: (i) (ii) Slottecl ALOHA Pure ALOHA

(i) Pure ALOHA

• In pure ALOHA, the stations transmit frames whenever they have data to send. • When two or more stations transmit simultaneously, there is collision and the frames are destroyed. • In pure ALOHA, whenever any station transmits a frame, it expects the acknowledgement from the receiver. • If acknowledgement is not received within specified time, the station assumes that the frame (or acknowledgement) has been destroyed. • If the frame is destroyed because of collision the station waits for a random amount of time and sends it again. This waiting time must be random otherwise same frames will collide again and again. • Therefore pure ALOHA dictates that when time-out period passes, each station must wait for a random amount of time before resending its frame. This randomness will help avoid more collisions. • Figure shows an example of frame collisions in pure ALOHA.

• In fig there are four stations that .contended with one another for access to shared channel. All these stations are transmitting frames. Some of these frames collide because multiple frames are in contention for the shared channel. Only two frames, frame 1.1 and frame 2.2 survive. All other frames are destroyed. • Whenever two frames try to occupy the channel at the same time, there will be a collision and both will be damaged. If first bit of a new frame overlaps with just the last bit of a frame almost finished, both frames will be totally destroyed and both will have to be retransmitted.

(ii) Slotted ALOHA

• Slotted ALOHA was invented to improve the efficiency of pure ALOHA as chances of collision in pure ALOHA are very high. • In slotted ALOHA, the time of the shared channel is divided into discrete intervals called slots. • The stations can send a frame only at the beginning of the slot and only one frame is sent in each slot.

• In slotted ALOHA, if any station is not able to place the frame onto the channel at the beginning of the slot i.e. it misses the time slot then the station has to wait until the beginning of the next time slot. • In slotted ALOHA, there is still a possibility of collision if two stations try to send at the beginning of the same time slot as shown in fig. • Slotted ALOHA still has an edge over pure ALOHA as chances of collision are reduced to one-half.

Protocol Flow Chart for ALOHA:

Fig. shows the protocol flow chart for ALOHA.

Explanation:

• A station which has a frame ready will send it. • Then it waits for some time. • If it receives the acknowledgement then the transmission is successful. • Otherwise the station uses a backoff strategy, and sends the packet again. • After many times if there is no acknowledgement then the station aborts the idea of transmission.

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ALOHA protocol
Aloha means "Hello". Aloha is a multiple access protocol at the datalink layer and proposes how multiple terminals access the medium without interference or collision. The protocol was developed by Norman Abramson and his colleagues at the University of Hawaii. The protocol

allows every system to send a frame if it ready to send. But when a collision occurs the node will wait for a random amount time and then send the frame again. The process continues till the node has sent all the frames. Since the nodes send their frames without sensing the medium there is a high probability for collisions to occur. The maximum success rate or throughput that can be achieved with Aloha protocol is only 18%. In 1972 Roberts developed a protocol that would increase the capacity of aloha two fold. The Slotted Aloha protocol involves dividing the time interval into discrete slots and each slot interval corresponds to the time period of one frame. This method requires synchronization between the sending nodes to prevent collisions. Posted by Keerthi at 6:40 PM 4 comments: job said... 日日日,日日,日日,日日日,徵才,日日日日,日日,日日日,徵信公司,日日,日日,日日,日日,日日,日日日,婚外情,日日日,日日 日,日日,日日,日日日日,日日日日日,抓姦,日日,債務協商,日日日日,日日,日日,日日日,法律諮詢,法律常識,日日 諮諮,日日,日日,日日日,GPS,日日,徵信公司,日日,抓姦,日日,日日,日日日,徵信公司,日日,抓姦,日日,日日,日日日, 徵信公司,日日,抓姦,日日,日日,日日日,徵信公司,日日,抓姦,日日,日日日 May 6, 2010 at 10:17 AM Sushil said... nice explanation.... thank you July 29, 2011 at 1:21 AM symirna said... Fantastic blog... Great... May 24, 2012 at 3:16 AM annonymous said... thanks......nice December 18, 2012 at 7:03 PM Post a Comment Newer Post Older Post Home

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