International Journal of Computer Applications (0975 – 8887) Volume 52– No.13, August 2012 19 Comparative Analysis of Different TCP Variants in Mobile Ad-Hoc Network Hrituparna Paul Research Scholar Dept. of Comp. Sc. Assam University Anish Kumar Saha Asstt. Professor Dept. of Comp Sc & Engg. N.I.T Agartala Partha Pratim Deb M.Tech CSE Netaji Subhash Engg College West Bengal, India Partha Sarathi Bhattacharjee Research Scholar Dept. of Comp. Sc. Assam University, Silchar ABSTRACT Mobile Ad-Hoc Network is an autonomous group of mobile users that communicate using wireless links with no support from any pre-existing infrastructure network and used as a highly reliable end-to-end protocol for transporting applications. But in wireless networks suffers from significant throughput degradation and delays. It uses Congestion Control and Avoidance algorithms which degrades end-to-end performance in wireless system. In this paper we have analyzed the performance of tcp algorithms with AODV, DSR and TORA for throughput. The effect of throughput on the TCP variants New Reno, Reno and Tahoe with different node scenarios was studied. Keyword TCP Variants, Throughput. 1. INTRODUCTION Mobile Ad Hoc Networks (MANETs) are wireless mobile nodes or an autonomous group of mobile users that cooperatively form a network without infrastructure. This network allows devices to create a network on demand without prior coordination or configuration and nodes within a MANET are involved in routing and forwarding information between neighbors. There is a direct communication among neighboring devices in MANETs but communication between non-neighboring devices requires a routing algorithm. A lot of work has been done on routing protocols since they are critical to the functioning of ad-hoc networks [1], [2], [3] Within the two categories of routing protocols described in literature: Proactive and Reactive, it is more suited for highly mobile ad hoc networks due to its ability to cope with rapidly changing network topologies. Because there is no coordination or configuration prior to setup of a MANET, there are several challenges and these challenges include routing packets in an environment where the topology is changing frequently and the task of locating a node and maintain a path to it becomes increasingly in the face of node mobility. Transport Control Protocol /Internet Protocol (TCP/IP) is a connection oriented protocol of the transport layer. It provides features like flow control, reliability and congestion control. It has been very effective in data transmission delivery and have also developed variants to possess the possibility to increase performance and multiple packet loss recovery. Today, the TCP is extensively tuned to provide high-quality performance in the conventional wired network. In fact, the TCP is responsible for providing reliable data transport in the Internet. However, it cannot offer reliable service while using e-mail, internet search and file transmission in a MANET. This protocol is a standard networking protocol on the internet and is the most widely used transport protocol for data services like file transfer, e-mail and WWW browser. It is primarily designed for wire-line networks, faces performance degradation when applied to the ad hoc scenario. In addition, various routing protocols behave differently over the variants of TCP. It is essential to understand the performance of different MANET routing protocols under TCP variants. In this paper, we have done a performance analysis of MANET Routing Protocols over different TCP Variants. The paper is organised as follows. Section 1 provides Introduction. Section 2 describes the Standard TCP congestion control algorithms. Section 3 describes the various TCP variants. Section 4 presents the simulation setup of our work. Finally Section 5 gives the future scope of our work concludes the paper. 2. TCP CONGESTION CONTROL ALGORITHMS The four algorithms, Slow Start, Congestion Avoidance, Fast Retransmit and Fast Recovery [4][5] are described below: 2.1. Slow Start [9] Slow Start, a requirement for TCP software implementations is a mechanism used by the sender to control the transmission rate, and also known as sender based flow control. This is accomplished through the return rate of acknowledgements from the receiver. In other words, the rate of acknowledgements returned by the receiver determines the rate at which the sender can transmit data. When a TCP connection first begins, the Slow Start algorithm initializes a congestion window to one segment, which is the maximum segment size (MSS) initialized by the receiver during the connection establishment phase and when acknowledgements are returned by the receiver, the congestion window increases by one segment for each acknowledgement returned. In this way, the sender can transmit the minimum of the congestion window and the advertised window of the receiver, which is simply called the transmission window. At some point the congestion window may become too large for the network or network conditions may change such that packets may be dropped. Packets lost will trigger a timeout at the sender and when this happens, the sender goes into congestion avoidance mode. 2.2. Congestion Avoidance [9] During data transfer phase of a TCP connection the Slow Start algorithm is used. There may be a point during Slow Start that the network is forced to drop one or more packets due to