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Ubiquitous Computing and Communication Journal 1 TCP PERFORMANCE ANALYSIS FOR MOBILE AD HOC NETWORK USING ON- DEMAND ROUTING PROTOCOLS K.Kathiravan B S Abdur Rehman Crescent Engineering College Vandalur, Chennai – 48 Dr. S. Thamarai Selvi Professor MIT Chromepet Campus Anna University, Chennai – 14 A.Selvam BSA Crescent Engineering College Vandalur, Chennai – 48. ABSTRACT TCP optimization in mobile ad hoc networks MANETs is a challenging issue because of some unique characteristics of MANETs. Packet losses in MANETs are mainly due to congestion and frequent link failures but in case of wired networks packet losses are mainly due to congestion. To optimize TCP in MANETs we use congestion control and avoidance algorithms. In this paper, we describe an NS2- based simulation analysis of TCP using omni antennas over mobile ad-hoc network. In particular, we compare the performance of end to end protocols such as TCP-Newreno and TCP-SACK with the routing provided by AODV, DSR and DSDV protocols using omni directional antenna. We investigate the effects of varying node density, mobility of nodes and pause time of nodes has on TCP performance. Through simulation, we show that TCP throughput drops significantly when nodes move, due to TCP’s inability to recognize the difference between link failure and congestion. We compare the throughput performance between the TCP versions. Keywords: TCP, mobile ad hoc networks, wireless networks, Directional antenna. 1 INTRODUCTION Mobile ad hoc networks recent activities strongly indicate that mobile networks will be an integral part of future internetworks. On the other hand, the performance of the internet protocols in wireless networks has been reported to be much lower than in fixed networks. The main reason for the performance degradation is that the Transmission Control Protocol (TCP) works less efficiently in wireless networks. This problem is important, since TCP/IP is used by many Internet applications, such as e-mail, web browsing and remote login. Basically, TCP/IP protocol was designed for wired networks which provides end to end reliable communication between nodes and assures ordered delivery of packets. It also provides flow control and error control mechanisms. As it is still a successful protocol in wired networks, we adapt it to mobile ad hoc networks. In wired networks that uses packet losses are mainly due to congestion. But in case of ad hoc networks packet losses are due to congestion in the network and due to frequent link failures so when we adapt TCP to ad hoc networks it misinterprets the packet losses due to link failure as packet losses due to congestion and in the instance of a timeout, backing-off its retransmission timeout (RTO).This results in unnecessary reduction of transmission rate because of which throughput of the whole network degrades. In the presence of the high error rates and
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This note was uploaded on 03/19/2012 for the course COMPUTER S 2143 taught by Professor Singh during the Spring '12 term at Punjab Engineering College.

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