International Journal of Computer Applications (0975 – 8887) Volume 67– No.9, April 2013 60 Cross Layer based Congestion Control Scheme for Mobile Ad hoc Networks S.Sheeja Research Scholar Bharathiar University Coimbatore Ramachandra V.Pujeri, PhD. Vice Principal KGiSL Institute of Technology, Saravanampatti, Coimbatore ABSTRACT Mobile Ad Hoc Networks consists of mobile nodes which are organized in a random manner. It can communicate with each other without any centralized infrastructure. Due to congestion, the packet loss is heavily occurred in the particular link. In order to avoid congestion, cross layer based congestion control scheme is proposed for reducing the packet losses in the network. The proposed scheme contains four phases. In first phase, the cross layer design is proposed to ensure that the information sharing can be done between the different layers in protocol stack. In second phase, the congestion detection scheme is explored which attains packet loss rate and congestion scale factor. In third phase, congestion control is achieved using cross layer approach. Here the congestion route is determined based on the path gain, buffer tenancy fraction. In fourth, new packet format is proposed. Each node maintains the congestion scale value, buffer tenancy fractional value. By extensive simulation, the proposed scheme achieves better throughput, congestion ratio, packet delivery ratio, low end to end delay and overhead than the existing schemes. Keywords Congestion Scale factor, MANET, Buffer tenancy fraction, cross layer, queue length, mobility, speed, packet delivery ratio, throughput, end to end delay and overhead. 1. INTRODUCTION 1.1 Mobile Ad hoc Networks (MANETs) Mobile Ad hoc Networks (MANETs) are the collection of mobile nodes without any centralized infrastructure. Due to the presence of high mobility of the nodes, the packet loss occurs frequently in the network. So the network congestion may be induced at any time. This will lead to lack of communication, lack of support, and more overhead. The main characteristics of MANET are dynamic topology, no access point, energy constrained, battery constrained. Mobile ad hoc networks used in various potential applications like earthquake, search and rescue operations, etc. 1.2 Congestion Control in MANETs The main issue in MANET is congestion control. It is totally associated to control the incoming traffic into a telecommunication network. The solution is to send a reduced packet sending rate to overcome the effect of congestion effectively. In general, the Transmission Control Protocol mainly combines the congestion control and dependability mechanism without explicit feedback about the congestion position. The congestion control principles include packet conservation, Additive Increase and Multiplicative Decrease (AIMD) in sending rate, stable network. The other techniques for congestion control are end system flow control, network congestion control, network based congestion avoidance, and resource allotment The packet loss can be condensed by involving congestion control over a mobility and failure adaptive routing protocol at the network layer. The congestion causes following difficulties: More delay: Several congestion control mechanism takes much time for detecting congestion. It leads to heavy delay. Sometimes the usage of new routes in some critical situations is advisable. The main problem is the delay moving for route searching in on-demand routing protocol. High Overhead: Congestion control mechanism takes effort for processing and communication in new routes for discovering it. It also takes effort in multipath routing for maintaining the multi-paths, though there is another protocol. More packet losses: If the congestion is detected, the packets may be lost. Congestion control solution is applied either by decreasing the sending rate at the sender, or dropping packets at the intermediate nodes or by both methods to decrease the traffic load. If the high packet loss rate occurs, small throughput may be occurred in the network. 1.3. Cross Layer design Cross layer design [23] is said to be the violation of layered communication architecture in the protocol design with respect to the original architecture. This design emphasizes on the network performance by enabling the different layers of the communication stack to share state information or to coordinate their actions in order to jointly optimize network performance. Distributed algorithms can exploit a cross-layer design to enable each node to perform fine-grained optimizations locally whenever it detects changes in network state. Mobility causes changes for the physical layer (for e.g. interference levels), the data link layer (for e.g. link schedules), the routing layer (for e.g. new neighbouring nodes), and the transport layer (for e.g. connection timeouts). As such, a cross-layer based design enhances the capability of the node to manage its resources in the mobile environments Antenna arrays can also enable the reception of multiple packets simultaneously on the wireless channel and the data packets corresponding to several connections could also arrive simultaneously at a node. The cooperation of various layers such as routing, data link, and physical layer can ensure the forwarding of data for all the connections within time. 1.4. Need for Cross layer design Cross layer design [23] offers performance benefits for a particular system. In contrast, the architecture offers a model for sustained innovation in a system, so it offers long-term gains. The short-term performance gains of cross-layer design may be more significant for the network user to make efficient use of limited node resources. The following issues raise the need for cross layer design: