Table 1. Performance of Proactive Routing Protocols
Wireless Networking is an emerging technology that allows users to access information and services anywhere, regardless of their geographic areas over the past few years with the trend of mobile computing. Mobile Adhoc Network (MANET) has become one of the most important wireless communication mechanisms among all, unlike traditional network. MANET represents complex distributed systems that comprise wireless mobile nodes that can freely and dynamically self-organize temporarily. MANET is an autonomously self- organized networks without infrastructure support. In MANET, nodes can move arbitrarily. Therefore the network may experience rapid and unpredictable topology changes, because nodes in a MANET normally have limited transmission ranges, some nodes cannot communicate directly with each other. Routing in MANET potentially contains multiple hops, and every node in mobile ad hoc networks has the responsibility to act as a router. In MANET, network topology can dynamically be changed in an unpredictable manner since the nodes are free to move. Every single node in the MANET works as both receiver and transmitter. Each node directly communicates with others, when they are both within their communication ranges. All nodes work as routers and take path in discovery and maintenance of routes to other nodes in the network. In this paper, a review on the routing protocols for mobile adhoc networks, challenges, issues, and applications were presented. The objective of this study is the comparative analysis of various routing protocols for MANET in different manner.
The origin of Mobile Adhoc Networks (MANETs) can be traced back to DARPA packet radio network project in the year of 1972. First generation of MANETs were used for different military scenarios for aiding combat operations around 1970 and packet radio networks was the first adhoc network. Second generation from 1980 to mid 1990, named as survivable adaptive radio networks, developments were focused on the next advancement of MANETs developed during their first generation. Third generation of MANETs, notebook computers based on radio waves concept of commercial MANET were invented. The network is decentralized, where all network activities including discovering the topology and delivering messages must be executed by the nodes themselves (i.e. routing functionality will be incorporated into mobile nodes). Node mobility in an MANET causes frequent changes of the network topology. The insecurity of the wireless links, energy constraints, relatively poor physical protection of nodes in a hostile environment, and the vulnerability of statically configured security schemes have been identified as the major challenges. MANETs operate in a highly dynamic environment and due to which their topology cannot be always defined and limitation poses a problem of security of the network and there is always a need for optimized and secured routing protocol. Till now, a number of routing protocols have been developed for MANETs and the set of applications for MANETs is diverse, ranging from small, static networks that are constrained by power sources, to large-scale, mobile, highly dynamic networks. In ad hoc networks, nodes do not have a priori knowledge of topology of network around them, they have to discover it.
Mobile Adhoc Networks (MANETs) represent a new form of communication consisting of mobile wireless terminals, where it is an infrastructure-less IP based network of mobile and wireless machine nodes connected with radio. In recent years, MANET has gained popularity and lots of research is being done on different aspects of MANET. It is an infrastructure-less network having no fixed base stations. MANET is characterized by dynamic topology, low bandwidth, and low power consumption. All the nodes in the network are moving, i.e. topology of the network is dynamic so the nodes can act both as host as well as router to route information necessary for its use. Nodes of a MANET do not have a centralized administration mechanism. It is known for its routable network properties, where each node act as a router to forward the traffic to other specified node in the network. MANET is a wireless multihop network without any fixed infrastructure, in contrast to today's wireless communications, which is based on fixed, pre-established infrastructure. All networking functions, such as determining the network topology, multiple accesses, and routing of data over the most appropriate paths, must be performed in a distributed way. These tasks are particularly challenging, due to the limited communication bandwidth available in the wireless channel.
MANET is formed dynamically by an autonomous system of mobile nodes that are connected via wireless links without using the existing network infrastructure or centralized administration. The nodes 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. Mobile ad hoc networks are infrastructure-less networks since they do not require any fixed infrastructure, such as a base station, for their operation. In general, routes between nodes in an ad hoc network may include multiple hops, and hence it is appropriate to call such networks as ''multi-hop wireless ad hoc networks”. Each node will be able to communicate directly with any other node that resides within its transmission range.
Nodes are free to move arbitrarily in any direction, thus the topology of the network changes unpredictably.
The bandwidth available for wireless networks is generally low than that of wired networks. The throughput of these networks is generally low due to various noises, fading effects, etc.
The nodes are portable devices and are dependent on batteries. This is the most important design consideration of the MANET.
Wireless networks are more prone to threats than wired networks. The increased possibility of various security attacks like eavesdropping, and denial of service should be handled.
The performance of query control schemes for the zone routing protocol were analyzed by [1]. Performance comparison of routing protocol in MANET was studied and discussed by [2]. Improving routing performance in Wireless Ad-hoc Networks using cross-layer interactions were discussed by [3]. Mobility sensitive approach for efficient routing in Ad-hoc Mobile Networks has been studied by [4]. Adaptive cell relay routing protocol for Mobile Ad-hoc Networks have been discussed by [5]. Analyzing control traffic overhead versus mobility and data traffic activity in Mobile Adhoc Network protocols were studied by [6]. Routing Strategy for Heterogeneous Mobile Adhoc Networks have been discussed by [7]. Hierarchical proactive routing mechanisms for Mobile Adhoc Networks have been analyzed by [8]. A review of routing protocols for Mobile Ad-hoc Networks have been studied and discussed by [9]. The study of MANET routing protocols by GloMoSim simulator were analyzed and discussed by [10]. A routing protocol based on node density for ad hoc networks were studied by [11]. The performance study of adhoc reactive routing protocols were studied by [12]. The performance analysis of Reactive Routing Protocols in Mobile Adhoc Networks have been analyzed and discussed by [13]. The performance evaluation and comparison of different adhoc protocols have been studied by [14]. Mobile adhoc networking imperatives and challenges have studied and discussed by [15].
A routing protocol specifies, how routers communicate with each and every information that enables them to select routes between any two nodes on a MANET. Routing algorithms determine the specific choice of route. Each router has a priori knowledge only of networks attached to it directly. A routing protocol shares this information first among immediate neighbors, and then throughout the network. Generally, there are two different stages in routing; they are route discovery and data forwarding. In route discovery, route to a destination will be discovered by broadcasting the query. Once the route has been established, data forwarding will be initiated and sent via the routes that have been determined. The energy consumption, route relaying load, battery life, and reduction in the frequency of sending control messages, optimization of size of control headers and efficient route reconfiguration should be considered when developing a routing protocol. A routing protocol is needed whenever a packet needs to be transmitted to a destination via number of nodes and numerous routing protocols have been proposed for such a kind of MANET. Routing protocols can be broadly classified into three types as, Table-driven (or) Proactive routing protocol, On-demand (or) Reactive routing protocol, and Hybrid routing protocol.
Proactive Routing Protocols are also called as table driven routing protocols approach in which every node generates routing information periodically to maintain and construct routing tables even if there is no data traffic to deliver. Information contained in routing tables is updated when the topology changes at every moment. Every node maintains routing information to every other node in the network. Proactive routing protocols may use either hop-by-hop or source routing strategies to forward data traffic. The performance of the network degrades due to the exchange of control traffic messages, but the packets experience less latency because the routes are always constructed and maintained for eventual data traffic. Proactive protocols work better in networks with low mobility.
Reactive Routing Protocols discovery and maintenance of routes are delayed until necessary, when a node needs to send a packet to any other node in the network. The sender node initiates the process to construct a path to reach the destination. To discover a route, a node floods the route request messages through the network. When a node with a route to the destination is reached, a route replay message is sent back to the source node. Reactive protocols can be classified into two categories, source routing and hop-by-hop routing.
In this phase, the source node initiates route discovery on demand basis. Source nodes consults its route cache for the available route from source to destination, otherwise if the route is not present it initiates route discovery. The source node in the packet, includes the destination address of the node as well the address of the intermediate nodes to the destination.
Due to dynamic topology of the network cases of the route failure between the nodes arises due to link break, route maintenance is done. These protocols have acknowledgement mechanism due to which route maintenance is possible and the protocols add latency to the network due to the route discovery mechanism.
Hybrid Routing Protocols are a combination of proactive and reactive routing protocols. Proactive protocols have large overhead and less latency while reactive protocols have less overhead and more latency. So, Hybrid protocol is presented to overcome the shortcomings of both proactive and reactive routing protocols. Hybrid routing protocol is a combination of both proactive and reactive routing protocols. It uses the route discovery mechanism of reactive protocol and the table maintenance mechanism of proactive protocol so as to avoid latency and overhead problems in the network. Hybrid protocol is suitable for large networks where large numbers of nodes are present. In this, large network is divided into a set of zones where routing inside the zone is performed by using reactive approach and outside the zone routing is done using reactive approach.
In this section, the performance comparison of routing protocol (Proactive, Reactive, and Hybrid) for Mobile Adhoc Networks is carried out. The performance comparisons for proactive, reactive and hybrid routing protocols are presented in Tables 1, 2 and 3 respectively. Table 4 provides the advantages and disadvantages of routing protocols for Mobile Adhoc Networks. The performance comparisons of routing protocol for MANET are shown in Table 5, and the applications of MANET are mentioned in Table 6.
Table 1. Performance of Proactive Routing Protocols
Table 2. Performance of Reactive Routing Protocols
Table 3. Performance of Hybrid Routing Protocols
Table 4. Advantages & Disadvantages of MANET Routing Protocols
Table 5. Performance comparison of Routing Protocols in MANET
Table 6. MANET Applications
In Mobile Adhoc Networks (MANETs), mobility, traffic and node density are the main network conditions that significantly affects the performance of the entire network. In this paper, different simulations have been carried out to compare the performance of different routing protocols in heterogeneous networks. Current MANET routing protocols have an unidirectional link problem and do not scale well if node density is increasing. This shows that the current routing protocols for MANET are inadaptable for heterogeneous networking. More works need to be carried out to investigate the problems that rise with routing protocols in heterogeneous networking. In this paper, an effort has been made on the comparative study of Reactive, Proactive and Hybrid routing protocols. A comparison of three protocols has been presented in the form of a table. Various advantages, disadvantages, and applications of these protocols are also presented in the form of table. There are various shortcomings of these indifferent routing protocols and it is difficult to choose routing protocol for different situations as there is trade off between various protocols. The field of Mobile Adhoc Networks is very vast and there are various challenges that need to be met, these networks are going to have widespread use in the future.