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MANET ( Mobile Adhoc NETwork )

BY: rashmi | Category: Technology and Computers | Post Date: 2008-08-11
 



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INTRODUCTION - WHAT IS MANET

As the importance of computers in our daily life increases it also sets new demands for connectivity. Wired solutions have been around for a long time but there is increasing demand on working wireless solutions for connecting to the Internet, reading and sending E-mail messages, changing information in a meeting and so on. There are solutions to these needs, one being wireless local area network that is based on IEEE 802.11 standard. However, there is increasing need for connectivity in situations where there is no base station (i.e. backbone connection) available (for example two or more PDAs need to be connected). This is where ad hoc networks step in.

In Latin, ad hoc means "for this," further meaning "for this purpose only.- It is a good and emblematic description of the idea why ad hoc networks are needed. They can be set up anywhere without any need for external infrastructure (like wires or base stations). They are often mobile and that's why a term MANET is often used when talking about Mobile Ad hoc NETworks. MANETs are often defined as follows: A "mobile ad hoc network" (MANET) is an autonomous system of mobile routers (and associated hosts) connected by wireless links - the union of which forms an arbitrary graph. The routers are free to move randomly and organize themselves arbitrarily; thus, the network's wireless topology may change rapidly and unpredictably. Such a network may operate in a standalone fashion, or may be connected to the larger Internet.

The strength of the connection can change rapidly in time or even disappear completely. Nodes can appear, disappear and re-appear as the time goes on and all the time the network connections should work between the nodes that are part of it. As one can easily imagine, the situation in ad hoc networks with respect to ensuring connectivity and robustness is much more demanding than in the wired case.


Ad hoc networks are networks are not (necessarily) connected to any static (i.e. wired) infrastructure. An ad-hoc network is a LAN or other small network, especially one with wireless connections, in which some of the network devices are part of the network only for the duration of a communications session or, in the case of mobile or portable devices, while in some close proximity to the rest of the network.

The ad hoc network is a communication network without a pre-exist network infrastructure. In cellular networks, there is a network infrastructure represented by the base-stations, Radio network controllers, etc. In ad hoc networks every communication terminal (or radio terminal RT) communicates with its partner to perform peer to peer communication. If the required RT is not a neighbour to the initiated call RT (outside the coverage area of the RT), then the other intermediate RTs are used to perform the communication link. This is called multi-hope peer to peer communication. This collaboration between the RTs is very important in the ad hoc networks. In ad hoc networks all the communication network protocols should be distributed throughout the communication terminals (i.e. the communication terminals should be independent and highly cooperative).

CHARACTERISTICS

Mobile Adhoc Network (MANET) is a collection of independent mobile nodes that can communicate to each other via radio waves. The mobile nodes that are in radio range of each other can directly communicate, whereas others needs the aid of intermediate nodes to route their packets. These networks are fully distributed, and can work at any place without the help of any infrastructure. This property makes these networks highly exible and robost.

The characteristics of these networks are summarized as follows:

Communication via wireless means.

Nodes can perform the roles of both hosts and routers.

No centralized controller and infrastructure. Intrinsic mutual trust.

Dynamic network topology. Frequent routing updates.

Autonomous, no infrastructure needed.

Can be set up anywhere.

Energy constraints

Limited security

Generally, the communication terminals have a mobility nature which makes the topology of the distributed networks time varying. The dynamical nature of the network topology increases the challenges of the design of ad hoc networks. Each radio terminal is usually powered by energy limited power source (as rechargeable batteries). The power consumption of each radio terminal could be divided generally into three parts, power consumption for data processing inside the RT, power consumption to transmit its own information to the destination, and finally the power consumption when the RT is used as a router, i.e. forwarding the information to another RT in the network. The energy consumption is a critical issue in the design of the ad hoc networks.

The mobile devices usually have limited storage and low computational capabilities. They heavily depend on other hosts and resources for data access and information processing. A reliable network topology must be assured through efficient and secure routing protocols for Ad Hoc networks.

APPLICATION AREAS

Some of the applications of MANETs are

Military or police exercises.
Disaster relief operations.
Mine site operations.
Urgent Business meetings
Robot data acquisition

It is easy to imagine a number of applications where this type of properties would bring benefits. One interesting research area is inter-vehicle communications. It is one area where the ad hoc networks could really change the way we communicate covering personal vehicles as well as professional mobile communication needs. Also, it is area where no conventional (i.e. wired) solutions would do because of the high level of mobility. When considering demanding surroundings, say mines for example, then neither would the base station approach work but we must be able to accomplish routing via nodes that are part of the network i.e. we have to use ad hoc network.

Such networks can be used to enable next generation of battlefield applications envisioned by the military including situation awareness systems for maneuvering war fighters, and remotely deployed unmanned micro-sensor networks. Ad Hoc networks can provide communication for civilian applications, such as disaster recovery and message exchanges among medical and security personnel involved in rescue missions.

NETWORK SECURITY

Network security extends computer security, thus all the things in computer security are still valid, but there are other things to consider as well. Computer security is defined as follows:

-Broadly speaking, security is keeping anyone from doing things you do not want them to do to, with, or from your computers or any peripherals- -William R. Cheswick.

Network security is then computer security plus secure communication between the computers or other devices. Not all nodes are computers in an Ad Hoc network, thus nodes cannot be assumed to implement the security services normally existent in computers' operating systems. That is why network security should be defined as:

-Making sure that the nodes enforce a proper computer security and then securing the communication between them-.


Different variables have different impact on security issues and design. Especially environment, origin, range, quality of service and security criticality are variables that affect the security in the network.

If the environment is concerned, networks can operate in hostile or friendly environments. A battlefield has totally different requirements for security if compared with home networks. On a battlefield also physical security and durability might be needed to ensure the functionality of the network.

The ways to implement security vary if the range of the network varies. If the nodes are very far from each others, the risk of security attacks increases. On the other hand, if the nodes are so close to each others that they actually can have a physical contact, some secret information (e.g. secret keys) can be transmitted between the nodes without sending them on air. That would increase the level of security, because the physical communication lines are more secure than wireless communication lines.

Quality of service issues deal with questions like -Is it crucial that all messages reach their destination?- or -Is it crucial that some information reaches the destination in certain time?-. QoS is generally demanded in real time applications where reliable and deterministic communication is required. These issues refer to security e.g. in process control applications. We could have an Ad Hoc network in some process and all the measurements and control signals could be transmitted through the network. In order to have secure and reliable control of the process, quality of service requirements need to be met.


The last variable of Ad Hoc networks described with respect to security is security criticality. This means that before we think of the ways to implement security, we must consider carefully whether security is required at all or whether it matters or not if someone outside can see what packets are sent and what they contain. Is the network threatened if false packets are inserted and old packets are retransmitted? Security issues are not always critical, but it might cost a lot to ensure it. Sometimes there is trade-off between security and costs.

Security Problems in MANETs

MANETs are much more vulnerable to attack than wired network. This is because of the following reasons :

Open Medium - Eavesdropping is more easier than in wired network.

Dynamically Changing Network Topology - Mobile Nodes comes and goes from the network, thereby allowing any malicious node to join the network without being detected.

Cooperative Algorithms - The routing algorithm of MANETs requires mutual trust between nodes which violates the principles of Network Security.

Lack of Centralized Monitoring - Absence of any centralized infrastructure prohibits any monitoring agent in the system.

Lack of Clear Line of Defense - The only use of I line of defense - attack prevention may not su ce. Experience of security research in wired world has taught us that we need to deploy layered security mechanisms because security is a process that is as secure as its weakest link . In addition to pre- vention, we need II line of defense - detection and response.


Advantages


The following are the advantages of MANETs:

They provide access to information and services regardless of geographic position.

These networks can be set up at any place and time.

These networks work without any pre-existing infrastructure.


Disadvantages


Some of the disadvantages of MANETs are:

Limited resources. Limited physical security.

Intrinsic mutual trust vulnerable to attacks. Lack of authorization facilities.

Volatile network topology makes it hard to detect malicious nodes.

Security protocols for wired networks cannot work for ad hoc networks.

CONCLUSION

Ad hoc networks can be implemented using various techniques like Bluetooth or WLAN for example. The definition itself does not imply any restrictions to the implementing devices.

Ad Hoc networks need very specialized security methods. There is no approach fitting all networks, because the nodes can be any devices. The computer security in the nodes depends on the type of node, and no assumptions on security can be made. In this paper the computer security issues have not been discussed, because the emphasis has been on network security.

But with the current MAC layer and routing solutions the true and working ad hoc network is just a dream for now. However, it can be used with relatively small networks and potentially some very nice applications can be realized. Although some peer-to-peer type of solutions work nicely already today, it would be nice to see that some new and innovative solutions would be seen in the arena of ad hoc networks since it is not hard for one to imagine a countless number of nice ad hoc based applications that would make the world at least a bit better place.

Article Source: http://www.saching.com



About Author / Additional Info: I am Rashmi from Bangalore. I am an engineering student and would like to share my knowledge through this website.

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Comments on this article: (2 comments so far)

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Comment Comment By Comment Date
MANET
Article is good,but you havn`t mentioned in detail about advantages and dis-advantages
Mohammed Aleem 2009-11-09
manet
rashmi your article is good but in this article u didn`t tell about which routing protocols are using in manets...
madhukarrao 2009-07-03



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