Computer Engineering and Intelligent Systems www.iiste.org ISSN 2222-1719 (Paper) ISSN 2222-2863 (Online) Vol 3, No.4, 2012 64 A Study of Congestion Aware Adaptive Routing Protocols in MANET Shitalkumar Jain, Shrikant Kokate, Pranita Thakur, Shubhangi Takalkar Maharashtra Academy of engineering, Alandi (D) Email: sajain@comp.maepune.ac.in Abstract Routing protocols for mobile ad hoc networks (MANETs) have been explored extensively in last few years. Much of this work is targeted at finding a feasible route from a source to a destination without considering current network traffic or application requirements. Routing may let a congestion happen which is detected by congestion control, but dealing with congestion in reactive manner results in longer delay, and unnecessary packet loss and requires significant overhead if a new route is needed. Routing should not be aware of, but also be adaptive to, network congestion. Adaptation to the congestion helps to increase both the effectiveness and efficiency of routing. These problems are solved by the congestion-aware routing protocols in certain degree. These protocols which are adaptive to congestion status of mobile ad-hoc network can greatly improve the network performance. In this paper, we present the survey of congestion adaptive routing protocols for mobile ad-hoc network. Finally, the future direction of congestion-aware routing protocols is described. Keywords: Ad hoc networks, congestion aware routing, Congestion metric, congestion adaptability 1. Introduction Wireless ad-hoc network is usually defined as a set of wireless mobile nodes dynamically self organizing a temporary network without any central administration or existing network infrastructure. The node in the wireless ad-hoc network can serve as routers and hosts. So, they can forward packets for other nodes if they are on route from source to destination. Routing is important problem in wireless ad-hoc network. Traditional working protocols cannot work well in wireless ad-hoc network because of the characteristics of the wireless ad-hoc networks. Since, mobile nodes have limited transmission capacity they mostly intercommunicate by multihop relay. Multihop routing is challenged by limited wireless bandwidth, low device power, dynamically changing network topology, high vulnerability to failure. To answer these challenges, many routing algorithms in MANETs were proposed. There are different dimensions to categorize them: proactive routing Vs reactive routing or single path routing Vs multipath routing. In proactive protocols, route between every two nodes are established in advance even though no transmission is in demand. In reactive protocols, route is discovered when needed transmission and released when transmission no longer takes place. Congestion is one of the most important restrictions of wireless ad-hoc network. It may deteriorate the performance of whole network. In the current design routing is not congestion-adaptive. Routing may let the congestion happen which is detected by congestion control. But dealing with congestion in reactive manner results in longer delay and an unnecessary packet loss and requires significant overhead if the new route is needed. But, now there is another dimension for categorizing for routing protocols: congestion adaptive Vs congestion un-adaptive routing. Our motivation is that congestion is dominant cause for packet loss, long delay, and high overhead in MANETs. These problems become visible in large scale transmission of traffic intensive data such as multimedia data where congestion is more probable and negative impact of packet loss on the service quality is of more significance. In this paper we studied congestion routing protocols like CRP(Congestion Adaptive Routing Protocol)[7],ECARP (Efficient Congestion Adaptive Routing Protocol )[11],CARP(Congestion Aware Routing Protocol),CADV(Congestion Aware Distance Vector)[12],CARA(Congestion Aware Routing plus rate Adaptation)[12],CARM(Congestion Aware Routing Protocol for Mobile Ad-hoc Network)[12].