This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.
The rapid growing of using mobile devices (e.g. laptops, mobile phones, personal digital assistants [PDAs]) in the recent years has made a need of some system or a network that collect these omnipresent devices together, therefore people can get access to the electronic platforms and searching for the information they need wherever and whenever they might be .The nature of these omnipresent devices makes Mobile Ad-Hoc Networks (MANETs) the most appropriate solution for such situations.
Mobile Ad-Hoc networks (MANETs) are independent systems which contain a collection of mobile devices that communicate with each other over wireless connection. They are self-organized, self-controlled and infrastructure-less networks. In this type of network each device is equipped with a wireless transceiver system which allows it to communicate with other devices over wireless channels. All devices can behave as routers to guarantee data packets to be delivered to their final destinations. That means, ad-hoc networks allow for multi-hop transmission of data packets between devices out of the transmission range of each other . These networks can be created or deployed in any place and at any time because they are decentralized and they not need any existing network infrastructure. These networks have been used widely in several different application such military, researchers, business, students, and emergency services .
C:\Users\The white bird\Desktop\adhocnet.gif
Figure 3.1 Simple Mobile Ad hoc Network
Characteristics of MANETs
A Mobile Ad hoc Network consists of mobile nodes which are free to move about arbitrarily. Theses nodes might be for example located in or on airplanes, ships, trucks and cars. A MANET is an autonomous system of mobile unites. The system is able to operate in isolation, or may have gateways to a fixed network. The nodes of MANET are equipped with wireless transmitters and receivers using antennas which may be omni-directional, highly-directional or a combination of both. At a given point in time, the ad hoc topology may change with time as the nodes move or adjust their transmission and reception parameters .
MANETs have several characteristics:
In some situations or places where no fixed infrastructure is available, users of mobile devices may need to communicate, for example, a team of students need to interact during a class, researchers want to run into each other in a conference room and wish to share files, or a group of emergency rescue team need to be rapidly deployed after some disaster . In such situations, mobile ad-hoc network comes out to work effectively without the need of any established infrastructure or centralized administration.
MANET nodes are free to move arbitrarily therefore, the network topology which is typically multi-hop may change randomly and rapidly at unpredictable times, and may consist of both bidirectional and unidirectional links.
The most important advantage of wireless mobile communication systems is its support of mobility . MANET nodes can move around while communicating with each other. And due to the absence of the base stations or other consecrated routers, each node is itself a router or for certain protocols is qualified to become a router.
Wireless links have considerably lower capacity than their hardwired counterparts. Moreover, the throughput of wireless communications with the effects of noise, fading, multiple access and interference conditions is often less than a radio's maximum transmission rate. In MANET, aggregate application demand will likely approach or exceed network capacity frequently. As the mobile network is often simply an extension of the fixed network infrastructure, mobile ad hoc users will demand similar services. These demands will continue to increase as multimedia computing and collaborative networking applications rise.
In a MANET, the nodes depend totally on batteries or other exhaustible means for their energy. Thus, the most important system design criteria for optimization might be energy conservation.
Limited physical security
In general, mobile wireless networks are more susceptible to physical security threats than are wired networks. In such networks, the possibility of eavesdropping, spoofing, and denial-of-service attacks is high and should be carefully considered. To reduce security threats, the existing link security techniques are often applied within wireless networks. As an advantage, in MANETs the decentralized nature of the network control provides additional robustness against the single points of failure of more centralized approaches.
Advantages of Mobile Ad-hoc Networks
The mobile ad-hoc networks have numerous advantages over conventional wireless networks including ease of deployment, speed of deployment, and decreased dependency on a fixed infrastructure.
Easy to deploy
Minimum arrangement and rapid deployment make ad-hoc networks appropriate for disasters and emergency situations. It is easy to deploy a mobile ad-hoc network as to deploy a mobile ad-hoc network, there is no pre-established infrastructure is required. Freely moving nodes can connect with each other without any complicated configurations.
Speed of deployment
The biggest advantage of mobile ad-hoc network is its rapid deployment. In the crisis situations, like emergencies and disasters where no pre-establish infrastructure is available or damaged and prompt deployment of network is required, Mobile ad-hoc network is best fit for these kind of situations.
Lessen dependence on infrastructure
The mobile ad-hoc is a wireless network which works without dependency on pre-established infrastructure. As in conventional wireless networks in a cell base station (BS) is responsible of the administration of the network like addition and deletion of the nodes from network. Moreover, Base station can access all the nodes within the cell so there is no need for broadcasting to find the route for transmission. Since in mobile ad-hoc networks no such centralized node is available therefore communication does not depends on fixed infrastructure.
Limitation of Mobile Ad hoc Networks
Beside the benefits or advantages of mobile ad-hoc networks there are also some limitation. Due to these limitations loads of research has been done in this area. Some of the limitations are following.
Limited wireless transmission range
In a mobile ad-hoc network, the medium of communication is radio transmission. The devices involved such type of networks are battery based. The transmission range of these devices is limited due to interference. The nodes located on smaller distance can communicate directly with each other, otherwise intermediate nodes provide interface for the nodes located out of the range.
Broadcast nature of the wireless medium
The transmission in mobile ad-hoc networks is done by broadcasting the information to all nodes within the range. This broadcast nature of mobile ad-hoc network in fact waist the bandwidth as well as other resource of the engaged devices. Due to Broadcast nature of medium there are more chances of redundancy and collision of packets which result in broadcast storm problem.
Packet losses due to transmission errors
As in the mobile ad-hoc networks there is no central assistance is available, transmission is done by nodes itself. So, chances of error in transmission are more as compare to fixed infrastructure based network. Due to the broadcast nature of mobile ad-hoc network, there are possibilities of interference and collision of packets which results in packet loss.
Route changes due to mobility
Mobility is the key feature of mobile ad-hoc network. There is no restriction on the movement of the nodes. This mobility of nodes actually changes the route of the transmission which require more processing of the nodes to discover new path for the transmission of the information.
Another effect of mobility in mobile ad-hoc network is packet loss. The nodes in mobile ad-hoc networks are always moving around randomly. This mobility of nodes disturbs the communication flow and result in packet loss.
All participating devices in the mobile ad-hoc networks depend on battery. This property of the mobile ad-hoc network limits the life of the communication. Suppose if a node (PDA, mobile phone, laptop) is acting as an intermediate node in a communication string and if its battery power becomes dead, will ultimately effect the transmission of other nodes as well.
The transmission on wireless networks is more risky as compare to wired networks. The mobile ad-hoc networks it is hard to secure data from insecure zone. Therefore this type of insecure transmission is quite attractive for hackers to do spy activities.
Routing Protocols for MANETs
In a mobile ad-hoc network nodes in the network perform the routing function. The transmission range in mobile ad-hoc is limited therefore routing in such networks rely on multiple hops. So, to accomplish the communication task nodes depend on each other to forward message to the target. Since the dynamic nature of the topology which demands two basic requirements on the routing protocol. First requirement is that it should be distributed and secondly it should calculate many, loop free routes.
Routing protocols for MANETs
Generally we can categorize the routing protocols into three categories on the bases of their functionality.
Figure 3.2 Classification of Routing Protocols for MANET
Proactive routing protocols or table driven (DSDV, OLSR, WRP, CGSR, others)
Reactive routing protocols or source initiated (DSR, LMR, AODV, ABR, others)
Hybrid protocols, like ZRP.
Every routing protocol has its own pros and cons. A protocol which is good for certain situation or condition might not be good for a different condition.
They are typically table-driven and distance-vector protocols, thus they resemble many traditional protocols. In proactive protocols the nodes periodically refresh of the existing routing information so that every node can immediately operate with consistent and up-to-date routing tables whenever there is data to be sent. The pure proactive protocols do not suite ad hoc networks due to constant and heavy control traffic delivery between the nodes. Especially in MANET networks there often needs to exist several alternate paths to the destination for reliability reasons, which causes frequent exchange of redundant control information.
They are also called source-initiated on-demand protocols, in contrary to the proactive protocols, they do not periodically update the routing information - it is propagated to the nodes only when necessary. Many of the MANET routing protocols are on-demand driven for optimization purposes. The disadvantage of the reactive protocols is that they create a lot of overhead when the route is being determined, since the routes are not necessarily up-to-date when required.
They make use of both reactive and proactive approaches. They typically offer means to switch dynamically between the reactive and proactive parts of the protocol. For instance, table-driven protocols could be used between networks and on-demand protocols inside the networks or vice versa. It seems that networks neither the pure proactive nor the reactive approach is sufficient, due to the mentioned problems, so the hybrid approach may be in general the optimal choice.