Figure 1. Ad hoc Routing Protocols
Mobile Ad Hoc Network (MANET) is a collection of multi-hop wireless mobile nodes that communicate with each other without centralized control or established infrastructure. The wireless links in this network are highly error prone and can go down frequently due to mobility of nodes, interference and less infrastructure. Therefore, routing in MANET is a critical task due to highly dynamic environment. In recent years, several routing protocols have been proposed for Mobile Ad hoc Networks and prominent among them are DSR (Dynamic Source Routing), AODV (Ad hoc On-demand Distance Vector) and TORA (Temporary Ordered Routing Algorithm). This paper provides an overview of these protocols by presenting their advantages and disadvantages of the proactive, reactive and hierarchical protocols and then make a comparative analysis of their advantages and disadvantages. The objective is to make observations about how the advantages and disadvantages of these protocols can be improved.
The absence of fixed infrastructure in a MANET poses several types of challenges [6]. The biggest challenge among them is routing. Routing is the process of selecting paths in a network along which to send data packets. An ad hoc routing protocol is a convention, or standard, that controls how nodes decide which way to route packets between computing devices in a Mobile Ad-hoc Network. In ad hoc networks, nodes do not start out familiar with the topology of their networks; instead, they have to discover it. The basic idea is that a new node may announce its presence and should listen for announcements broadcast by its neighbors. Each node learns about nearby nodes and how to reach them, and may announce that it can reach them too. The routing process usually directs forwarding on the basis of routing tables which maintain a record of the routes to various network destinations. Mobile networks can be classified into infrastructure networks and Mobile Ad hoc Networks [1] according to their dependence on fixed infrastructures. In an infrastructure mobile network, mobile nodes have wired access points within their transmission range. In contrast, Mobile Ad hoc Networks are autonomously self-organized networks without infrastructure support. In a Mobile Ad hoc Network, nodes move arbitrarily, therefore the network may experience rapid and unpredictable topology changes.
Classification methods help researchers and designers to understand distinct characteristics of a routing protocol and find its relationship with others. Figure 1 shows the Characteristics of Routing Protocols.
Figure 1. Ad hoc Routing Protocols
Every proactive routing protocol usually needs to maintain accurate information in their routing tables. It attempts to continuously evaluate all of the routes within a network. This means the protocol maintains fresh lists of destinations and their routes by periodically distributing routing tables throughout the network. Once the routing tables are setup, then data (packets) transmissions will be as fast and easy as in the tradition wired networks. This section, contains three popular proactive routing protocols – DSDV, WRP and OLSR.
Destination-Sequenced Distance-Vector Routing (DSDV) [10] is a table-driven routing scheme for ad hoc mobile networks based on the Bellman-Ford algorithm [3]. It was developed by C. Perkins and P. Bhagwat in 1994. The main contribution of the algorithm was to solve the routing loop problem.
The Wireless Routing Protocol (WRP) [8] is a proactive unicast routing protocol for MANETs. WRP uses an enhanced version of the distance-vector routing protocol, which uses the Bellman-Ford algorithm to calculate paths. Because of the mobile nature of the nodes within the MANET, the protocol introduces mechanisms which reduce route loops and ensure reliable message exchanges.
The Optimized Link State Routing Protocol (OLSR) [4] is an IP routing protocol optimized for Mobile Ad-hoc Networks, which can also be used on other wireless ad-hoc networks. It uses Hello and Topology Control (TC) messages to discover and then disseminate link state information throughout the mobile adhoc network. Individual nodes use this topology information to compute next hop destinations for all nodes in the network using shortest hop forwarding paths. Table 1 shows three Proactive Routing Protocols, comparing individual advantages and disadvantages.
Table 1. Comparison between DSDV, WRP and OLSR
In bandwidth-starved and power-starved environments, it is interesting to keep the network silent when there is no traffic to be routed. Reactive routing protocols do not maintain routes, but build them on demand. A reactive protocol [5] finds a route on demand by flooding the network with Route Request packets.
1. No big overhead for global routing table maintenance as in proactive protocols.
2. Quick reaction for network restructure and node failure.
1. High latency time in route finding.
2. Excessive flooding can lead to network clogging.
There are many reactive routing protocols for MANET. This section holds three protocols - AODV, DSR and SSA.
Ad hoc On-Demand Distance Vector (AODV) [7] Routing is a routing protocol for Mobile Ad hoc Networks (MANETs) and other wireless ad-hoc networks. It is jointly developed in Nokia Research Center, University of California, Santa Barbara and University of Cincinnati by C.Perkins, E.Belding- Royer and S. Das. AODV is capable of both unicast and multicast routing. It is a reactive routing protocol, meaning that it establishes a route to a destination only on demand.
Dynamic Source Routing (DSR) [2] is a routing protocol for wireless mesh networks. It is similar to AODV in that it forms a route on-demand when a transmitting computer requests one. However, it uses source routing instead of relying on the routing table at each intermediate device. Many successive refinements have been made to DSR, including DSRFLOW. Determining source routes requires accumulating the address of each device between the source and destination during route discovery. The accumulated path information is cached by nodes processing the route discovery packets.
Signal Stability-Based Adaptive Routing Protocol (SSA) has on-demand behavior of routing protocol that selects longer-lived routes based on the signal strength and location stability of a node. SSR comprises of two cooperative protocols: the Dynamic Routing Protocol (DRP) and the Static Routing Protocol (SRP).The Dynamic routing protocol maintains the Signal Stability table (SST) and Routing table (RT). The SST keeps the signal strength of neighboring nodes acquired by periodic beacons from the link layer of every neighboring node. Signal strength is either recorded as a strong or weak channel. Table 2 shows three Reactive Routing Protocols, comparing individual advantages and disadvantages.
Table 2. Comparison between AODV, DSR and SSA
The main objective of hierarchical routing is to reduce energy consumption by classifying nodes into clusters. In Hierarchical Routing Protocol each cluster, a node is selected as the leader or the cluster head. The different schemes for hierarchical routings mainly differ in how the cluster head is selected and how the nodes behave in the inter and intra-cluster domain.
Low-Energy Adaptive Clustering Hierarchy (LEACH) [13] proposed by Heinzelman. Is one of the pioneering clustering routing approaches for WSNs. The main objective of LEACH is to select sensor nodes as CHs by rotation, so the high energy dissipation in communicating with the BS is spread to all sensor nodes in the network.
Hybrid Energy-Efficient Distributed clustering (HEED) [14] introduced by Younis and Fahmy, is a multi-hop WSN clustering algorithm which brings an energy-efficient clustering routing with explicit consideration of energy. Different from LEACH in the manner of CH election, HEED does not select nodes as CHs randomly. The manner of cluster construction is performed based on the hybrid combination of two parameters. One parameter depends on the node's residual energy, and the other parameter is the intra-cluster communication cost. In HEED, elected CHs have relatively high average residual energy compared to MNs.
Base-Station Controlled Dynamic Clustering Protocol (BCDCP) [9], was introduced by Muruganathan. It is a centralized clustering routing protocol with the BS being capable of complex computation. The main idea of BCDCP is the cluster formation where each CH serves an almost equal number of MNs to balance CH overload and uniform CH placement throughout the network. Table 3 shows three Hierarchical Routing Protocols, comparing individual advantages and disadvantages.
Table 3. Comparison between LEACH, HEED and BCDCP
This paper analyzes about MANETs routing protocols, and it is very useful to know about how to easily transfer the data. Particularly in AODV, LEACH more advantage is available and also using low energy consumption, lifetime is more. In future can implement efficient data transmission in MANETs.
In this paper the authors present a comparative study and description of reactive and proactive routing protocols. Reactive Routing protocols have less energy consumption than proactive routing protocols but at a high cost. This paper provides an overview of these protocols by presenting their advantages and disadvantages of the proactive, reactive and hierarchical protocols and then makes a comparative analysis so as to analyze their advantages and disadvantages. The objective is to make the observations about how the advantages and disadvantages of these protocols can be improved. Each protocol has its own advantage and disadvantage in different MANET settings or environments.