AdHoc Networks

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Dr Mrs U D Dalal

Ad-hoc Networks


Contents

Introduction History Mobile Ad-hoc Networks

Infrastructure based Networks and Infrastructure-less Networks.

Mobile Ad-hoc Network Routing Protocols Setting up a simple Mobile Ad-hoc Network Pros and Cons.

Wireless Ad-hoc Sensor Networks Classification, types, network structure, basic requirements.

Difference between Cellular and Ad-hoc Networks Future Research Directions Conclusions


Ad Hoc NetworksThe Need of “TIME”.

Today the networks normally developed are of the type having some fixed infrastructure. What would be the solution if the network is required to bemade for some short period of time?


Introduction

An Ad-hoc network is a local area network or some other small network, especially one with wireless (or temporary plug in connections), in which some of the network devices are the part of the network only for the duration of a communications session.

Allows new network devices to be quickly added. Each user has a unique network address that is

recognized as the part of the network.


A Simple Ad Hoc Network Example

Nodes or devices can join together to make up a simple ad-hoc network. Every device owes an equal status or designation in the network.


A Comparison Example

One organization, for example arranges a conference, and the attendees use their laptops or notebook computers to connect to the nearby computers and the Internet through the wireless router.


A Comparison Examplecont’d…

A better solution to this kind of network will be an ad-hoc network in which the wireless router is replaced by a wireless computer that can well act as a wireless router.

The computers communicate directly with each other.


Mobile Ad-hoc Networks

On the basis of infrastructure we can classify the Ad-hoc networks into two main categories. They are

1. Infrastructure-based networks. A network with pre-constructed infrastructure that is

made of fixed network nodes and gateways, with typically network services delivered via these preconfigured infrastructures.

For example, cellular networks are infrastructure-based networks built from PSTN backbone switches, MSCs, base stations, and mobile hosts.

Each node has its strict specific responsibility in the network. WLANs typically also fall into this category.


Mobile Ad-hoc Networks

2. Infrastructure-less networks In this case a network is formed dynamically through

the cooperation of an arbitrary set of independent nodes.

For example, two PCs equipped with wireless adapter cards can set up an independent network whenever they are within range of one another.

In mobile ad hoc networks, nodes are expected to behave as routers and take part in discovery and maintenance of routes to other nodes.

Network is decentralized where the topology discovering and the message delivering must be executed by the nodes themselves.


Mobile Ad-hoc Networks (MANETs) Routing Protocols

Ad-hoc Networks require efficient routing protocols because determining successful routing paths and delivering messages in a decentralized environment where network topology fluctuates is not a well defined problem.

An optimal route at a certain time may not work seconds later.

Discussed below are three categories that existing ad-hoc network routing protocols fall into: Table Driven Protocols On Demand Protocols Hybrid Protocols



Ad-hoc Mobile Routing Protocols

Table Driven Protocols On Demand Protocols

Hybrid Protocols

DSDV, WRP, STAR

ABR, DSR, AODV, TORA

ZRP



Table Driven Routing Protocol Send periodic updates of the routes. Each node uses routing information to store the location

information of other nodes in the network and this information is then used to move data among different nodes in the network.

Have lower latency since routes are maintained at all times

On Demand Routing Protocols Establish routes only when required to route data

packets. Route discovery process Have longer transmission delays.



Hybrid Routing Protocols Combine Table Based Routing Protocols with On

Demand Routing Protocols. They use distance-vectors to establish the optimum

routes, and report routing information only when there is a change in the topology of the network.

Each node in the network has its own routing zone, the size of which is defined by a zone radius, defined by a metric such as the number of nodes.

Each node keeps a record of routing information for its own zone.


Data Routing


Data Routing


Route Discovery in Mobile Ad-hoc Networks


Route Discovery in Mobile Ad-hoc Networks


An Interesting Scenario


Cont’d…


Cont’d…


Cont’d…


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Key Benefits of Mobile Ad-hoc Networks

No expensive infrastructure must be installed Use of unlicensed frequency spectrum Quick distribution of information around sender Use of ad-hoc networks can increase mobility and

flexibility, as ad-hoc networks can be brought up and torn down in a very short time.

Ad-hoc networks can be more economical in some cases, as they eliminate fixed infrastructure costs and reduce power consumption at mobile nodes.

Because of multi-hop support in ad-hoc networks, communication beyond the Line of Sight (LOS) is possible at high frequencies.


Key Benefits of Mobile Ad-hoc Networks

Multi-hop ad-hoc networks can reduce the power consumption of wireless devices. More transmission power is required for sending a signal over any distance in one long hop than in multiple shorter hops. It can easily be proved that the gain in transmission power consumption is proportional to the number of hops made.

Because of short communication links (multi-hop node-to-node communication instead of long-distance node to central base station communication), radio emission levels can be kept low. This reduces interference levels, increases spectrum reuse efficiency, and makes it possible to use unlicensed unregulated frequency bands.


Mobile Ad-hoc Design Issues and Constraints

They are Infrastructure-less Dynamically Changing Network Topologies Network Security Physical Layer Limitation Limited Link Bandwidth and Quality Variation in Link and Node Capabilities Quality of Service Network Scalability Network Management and Reliability Energy Constrained Operation


Wireless Ad-hoc Sensor Networks

A wireless ad hoc sensor network consists of a number of sensors spread across a geographical area.

Each sensor has wireless communication capability and some level of intelligence for signal processing and networking of the data.


Examples of Wireless Ad-hoc Sensor Networks

Military sensor networks to detect and gain as much information as possible about enemy movements, and other phenomena of interest. In a military sensor network, track an enemy tank as it moves through the geographic area covered by the network.

Also the military sensor networks designed to maintain a low probability of intercept and/or a low probability of detection. Hence the nodes prefer to radiate as little power as necessary and transmit as infrequently as possible, thus decreasing the probability of detection and interception.

Sensor networks to detect and characterize Chemical, Biological, Radiological, Nuclear, and Explosive material.


Classification of Wireless Sensor Networks

Individually addressable nodes. Group or mixed addressable nodes.


Basic Requirements of Ad-hoc Sensor Networks

Network self-organization: For large number of nodes and their potential placement in hostile locations, it is essential that the network be able to self-organized, manual configuration is not feasible. Moreover, nodes may fail (either from lack of energy or from physical destruction), and new nodes may join the network. Therefore, the network must be able to periodically reconfigure itself so that it can continue to function. Individual nodes may become disconnected from the rest of the network, but a high degree of connectivity must be maintained.

Large number of (mostly stationary) sensors: Required for the collection of information from different regions


Basic Requirements of Ad-hoc Sensor Networks

Collaborative signal processing: Yet another factor that distinguishes these networks from MANETs is that the end goal is detection/estimation of some events of interest, and not just communications.

Querying ability: A user may want to query an individual node or a group of nodes for information collected in the region. Various local nodes will collect the data from a given area and create summary messages.

Low energy use: Since in many applications the sensor nodes will be placed in a remote area, service of a node may not be possible. In this case, the lifetime of a node may be determined by the battery life, thereby requiring the minimization of energy expenditure.


Ad-hoc Network Sensor Types

Acoustic used as the sound sensors. Seismic for the prediction of earth quake. Infrared for short range communication. Still/Motion video camera.


Difference between Cellular and Ad-hoc Networks

Cellular Networks Ad-hoc Networks

Fixed, pre-located cell sites and base stations.

No fixed base stations, very rapid deployment.

Static backbone network topology Highly dynamic network topologies, with multi-hop.

Relatively favorable environment and stable connectivity.

Hostile environment (losses, noise) and irregular connectivity.

Detailed planning before base stations can be installed.

Ad-hoc network automatically forms and conforms to change.


Future Research Directions

Routing Protocol Optimization QoS Support Simulation Security Standardization and Interoperability


Conclusions

Ad hoc networking will play an important role in this evolution. Its intrinsic flexibility, ease of maintenance, lack of needed infrastructure, auto configuration, self-administration capabilities, and significant cost advantages make it a prime candidate for becoming the stalwart technology for personal pervasive communication

In moving forward and successfully fulfilling this opportunity, developing and seamlessly integrating MANET with other wireless networks and fixed internet infrastructures, the successful addressing of many of the open research and development issues will play a critical role


Thanks for Your Concentration.

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AdHoc Networks