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1.1 INTRODUCTION
Earthquake, which is a natural event, occurs periodically in some areas of the world causing greater economical losses, in addition to loss of human lives. Many Governments prepare to attend the relief measures with huge cost, only after the event is occurred. Even with advancement in modern science and technology, few informations are available on the prediction of earthquakes in advance. Even such methods have not been field tested universally. In the absence of the above, heavy losses both to human lives and materials, occur often and often. These areas needs further probing.
Against this, there are many seismological observatories throughout the world to record the intensity of these observatories only help to confirm the occurrence of the events but not to predict the event in advance. If the earthquake is predicted one to two days in advance, it is possible for any Government to take preventive measures against the losses. Though there are several methods are being followed to predict the earthquake (but the success story is different), this is the first time in the history, earthquake is predicted with the help of Artificial satellites (success rate is more than 75%!).
Mobile hosts and wireless networking hardware are becoming widely available, and extensive work has been done recently in integrating these elements into traditional networks such as the Internet. Often times, however, mobile users will want to communicate in situations in which no fixed wired infrastructure is available. In such situations, a collection of mobile hosts with wireless network interfaces may form a temporary network without the aid of any established infrastructure or centralized administration. These kinds of networks of mobile hosts have become known as ad hoc networks.
An ad hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any centralized administration or standard support services regularly available on the wide-area network to which the hosts may normally be connected.
AODV (Ad hoc On-demand Distance Vector) is a protocol that works dynamically to establish (RREQ &RREP) and maintain routes, adapting quickly to changing page link conditions. As its name implies, AODV is an on-demand routing protocol (reactive). Routes between nodes are built only as requested by source nodes. These routes are maintained locally until they are no longer needed by the source nodes or a page link breakage occurs.
1.2 BACKGROUND
Earthquake, which is a natural event, occurs periodically in some areas of the world causing greater economical losses, in addition to loss of human lives. Many Governments prepare to attend the relief measures with huge cost, only after the event is occurred. Even with advancement in modern science and technology, few informations are available on the prediction of earthquakes in advance. Even such methods have not been field tested universally. In the absence of the above, heavy losses both to human lives and materials, occur often and often. These areas needs further probing.
Against this, there are many seismological observatories throughout the world to record the intensity of these observatories only help to confirm the occurrence of the events but not to predict the event in advance. If the earthquake is predicted one to two days in advance, it is possible for any Government to take preventive measures against the losses. Though there are several methods are being followed to predict the earthquake (but the success story is different), this is the first time in the history, earthquake is predicted with the help of Artificial Satellites (success rate is more than 75% !).
The tremendous growth of personal computers and the handy usage of Mobile computers necessitate the need to sharing of information between computers. At present this sharing of information is difficult, as the users need to perform administrative tasks and set up static, bi-directional links between the computers. This motivates the construction of temporary networks with no wires and no communication infrastructure and no administrative intervention required. Such an interconnection between mobile computers is called an Ad Hoc network. In such an environment, it may be necessary for the mobile computers to take help of other computers in forwarding a packet to the destination due to the limited range of each Mobile host’s wireless transmission.
1.3 ASSOCIATED TECHNOLOGIES
1.3.1 Feasibility Study
The apparently random onset of large earthquakes in an earthquake-prone region requires that a constant state of earthquake readiness be maintained by populations and facilities in the area to assure minimal damage and loss of life. The balance between earthquake readiness and the conduct of normal life may shift more in favor of earthquake readiness if a few seconds to a few tens of seconds of warning can be given before strong ground motion from a large earthquake arrives. This is possible because elastic wave energy from a nearby earthquake travels slowly (3 to 6 km/s) compared to the speed of light. Consequently, if a large network of seismic sensors is distributed in an earthquake-prone region, some of these sensors will be close to any given earthquake epicenter and therefore will detect it first. This information can be transmitted at the speed of light to a central warning system that can broadcast an area-wide alarm in advance of the spreading elastic wave energy from the earthquake. This type of seismic network is called an Earthquake Alert System (EAS).
Although the basic concept for the system is simple, the implementation Of a modern EAS requires the use of diverse and fairly sophisticated existing technology in addition to new research and development on a number of operational issues, such as reliability, accuracy, and survivability.
Extensive networks of seismic stations that measure strong and weak ground motion and communicate in real time are required. A real-time central processing station must be developed that can transmit the location and magnitude as well as an estimate of the reliability of this information. Interfacing and emergency override control of an area-wide broadcast transmitter must also be accomplished. Finally, the user's receivers and warning-signal processing strategies must be developed
1.3.2 Distance Squenced Distance Vector routing: (DSDV)
Distance Sequenced Distance Vector (DSDV) routing protocol is a variant of distance vector routing method by which mobile nodes cooperate among themselves to form an Ad Hoc network. .DSDV is based on RIP (Routing Information Protocol), which is used for Intra-Domain routing in Internet. DSDV requires each node in the network to maintain complete list of distance information to reach each node in the Ad Hoc network. In DSDV, each node uses a Sequence Number, which is a counter that can be incremented only by that node. Each node increments the Sequence Number every time it sends an update message and this Sequence Number uniquely identifies the update messages sent from a particular node. Routing information is propagated using broadcast or multicasting the messages periodically or triggered upon a change in the topology. DSDV uses only bi-directional links for routing as it is based on Distance Vector Routing. So in DSDV, each node does not insert information into its Routing table received from other neighbors unless the node is sure that the other node can listen to its informations.
In DSDV, each node maintains a routing table and advertises this information to each of its neighbors periodically or immediately when there is a change in the topology. The routing data packet sent periodically by a node contains a new Sequence number and the following information for each of the other mobile stations:
1. The Destination address,
2. The number of hops required to reach the Destination,
3. The Sequence Number of the Destination received regarding the destination.
A node upon receiving a new routing information packet from its neighboring node compares it with the previous routing information packets and then updates its routing table depending on the sequence number and the metric of the entries. Any route with higher Sequence Number is always chosen regardless of the value of the metric. Routes with old Sequence Numbers are discarded. In case of same sequence number as the existing route, a route with the least cost metric is chosen. The metric chosen from the new routing information packet are each incremented by one. The routes that have changed are scheduled for immediate advertisements. Routes with a later Sequence Number are not scheduled for immediate advertisement and the time at which they are scheduled depends on the average settling time for routes to that particular destination but those routes are available for use though not advertised immediately. This is done to eliminate those updates that would occur if a better route were found very soon. Thus each node in DSDV maintains two routing tables, one used for forwarding the data packets and the other for advertising incremental routing packets.
CHAPTER 2
TECHNOLOGY AND TRENDS
2.1 TECHNOLOGY
2.1.1 Ad Hoc Network
An Ad Hoc network is a cooperative engagement of collection of Mobile Hosts without the intervention of any centralized Access Point. The idea is to design each Mobile host as a ‘specialized router’, which periodically advertises its view of the interconnection topology with other Mobile Hosts in the network.
Ad Hoc networks are needed as mobile hosts need to communicate with each with no fixed infrastructure and no administrative help because
1. It may not be physically possible for the establishment of the infrastructure or
2. It may not be practically economical to establish the infrastructure or
3. It may be because of the expediency of the situation does not permit the installation of the infrastructure.
Some of the situations, which motivate the construction of Ad Hoc networks, are
1. A class of students may need to interact during a lecture,
2. Any number of people entering a conferencing room wants to communicate with each other,
3. A group of emergency rescue workers may need to be quickly deployed after an earthquake or flood,
4. A group of friends or business associates run into each other at an airport terminal and wish to share information,
5. Ships to communicate with each other.
Need new routing protocols:
In Ad Hoc networks, we need new routing protocols because of the following reasons:
1. Nodes in Ad Hoc networks are mobile and topology of interconnections between them may be quite dynamic.
2. Existing protocols exhibit least desirable behavior when presented with a highly dynamic interconnection topology.
3. Existing routing protocols place too heavy a computational burden on each mobile computer in terms of the memory-size, processing power and power consumption.
4 Existing routing protocols are not designed for dynamic and self-starting behavior as required by users wishing to utilize Ad-Hoc networks.
5 Existing routing protocols like Distance Vector Protocol take a lot of time for convergence upon the failure of a link, which is very frequent in Ad Hoc networks.
6. Existing routing protocols suffer from looping problems either short lived or long lived.
7. Methods adopted to solve looping problems in traditional routing protocols may not be applicable to Ad Hoc networks.
Features desired for a Routing Protocol in Ad Hoc Networks:
The protocols to be used in the Ad Hoc networks should have the following features:
1. The protocol should adapt quickly to topology changes.
2. The protocol should provide Loop free routing.
3. The protocol should provide multiple routes from the source to destination and this will solve the problems of congestion to some extent.
4. The protocol should have minimal control message overhead due to exchange of routing information when topology changes occur.
5. The protocol should allow for quick establishment of routes so that they can be used before they become invalid.
