International Journal of Modern Communication Technologies & Research (IJMCTR) ISSN: 2321-0850, Volume-4, Issue-11, November 2016 13 www.erpublication.org Abstract— MANET is a peer-to-peer, multi-hop Mobile wireless network where nodes operate as hosts, generating traffic, and Routers, carrying control and data. Packets are transmitted in store and forward manner from source to destination. In this research paper we analyzed the impact of file size on the performance of AODV, DSR and OLSR under TCP traffic. We used different TCP Variant namely Tahoe, New-Reno, CUBIC and Standard TCP. We found that the file size have impact on network performance but the impact of TCP variant is not outstanding and the selection of suitable MANET protocol is more important than the selection of TCP variant. Index Terms—AODV, DSR, FTP, OLSR, TCP I. INTRODUCTION A mobile ad hoc network is an autonomous collection of mobile devices (laptops, smart phones, sensors, etc.) ; that communicate with each other over wireless links and cooperate in a distributed manner; in order to provide the necessary network functionality in the absence of a fixed infrastructure[1]. It is a peer-to-peer network where nodes operate as hosts, generating traffic, and Routers, carrying control and data. Nodes that are located within each other transmission range, can directly communicate, otherwise intermediate nodes will act as a router and relay data packets to their destinations. Many routing protocols have been designed for MANETs. Routing protocols in MANETs are classified as Proactive, Reactive and Hybrid. Proactive protocols (Table-driven) maintain fresh lists of destinations and their routes by periodically distributing routing tables throughout the network so that a source can find a route immediately when it needs it. Optimized Link -State Routing Protocol (OLSR) is an example of proactive routing protocols in MANET .Reactive or (On-demand) finds the route on-demand by flooding the network with route request packets. AdHoc-On-Demand Vector Routing protocol (AODV) and Dynamic Source Routing (DSR) are examples of Reactive protocols. Hybrid protocol combines the advantages of proactive and reactive routing. Zone Routing Protocol (ZRP) is an example of a hybrid protocols. The protocols studied in this research are AODV, DSR and OLSR. In this research paper we will study the Impact of application file size, on the performance of the protocols under study. Five different file sizes will be simulated for each protocol and, the performance parameters under study will be evaluated to find out which file(s) size is appropriate for each protocol. FTP is being used as the application where all the nodes in the network run multiple FTP sessions. Data will be Abdelmuti Ahmed Abbasher Ali, Faculty of Engineering-Elneelain University-Khartoum-Sudan Dr.Amin Babkir Abdelnabi Mustafa, Faculty of Engineering-Elneelain University-Khartoum-Sudan transmitted from one source (FTP server) to the destined node. When the application files size increase the volume of traffic do too. This will cause congestion on the nodes that are located near the source; which will degrade the overall performance of the network. The routing protocol should be able to find an alternative route to overcome congestion near the source (FTP Server).this research will also find out which of the protocols under study are able to avoid congestion by finding an alternative route. FTP uses TCP as the transport protocol; and after determining the best file size for the protocols under study; we will study the impact of TCP variants; namely New Reno, CUBIC, and Tahoe on the performance of routing protocols under study; to figure out the best TCP variant for the appropriate file size. Many researchers have investigated the impact of TCP variant on MANET routing Protocol. In reference [2] a comparison of the performance of TCP-Reno and TCP-Vegas over MANET had been performed. The researchers concluded that the performance difference between TCP-Reno and TCP-Vegas over any selected routing protocol is irrelevant; and the selected routing protocol is more important than the selected TCP variant. In reference [3] a comparison study of TCP-Reno, TCP-New Reno and TCP-SACK has been performed. The results of the comparison is that in a high density network when congestions and packet error rates are very likely, TCP SACK outperforms other variants in terms of retransmission attempts, upload and download response time. With the variations of mobility rates, TCP Reno dominates other congestion control algorithms in most of the cases. In Reference [4] the authors has carried out a comparison of performance of TCP over MANET. The TCP variant implemented were Reno, New-Reno and SACK under different scenarios related to mobility and network size. The study concluded that out of the three, the SACK variant can adapt relatively well to the changing network sizes while the Reno performs most robustly in different mobility scenarios. II. TCP IN MANET TCP is an end-to-end and reliable transport protocol. It was originally designed for wired networks. There are several factors that influence TCP performance in MANET, such as dynamic topology, shared medium, high Bit Error Rate (BER) and signal fading [6].One of the important aspect of TCP is congestion control[5].TCP interpret a packet loss as an indicator of congestion. In MANET packet loss can occur as a result of a link failure or other errors, but this loss will be interpreted by TCP as congestion, so TCP invokes congestion mechanisms. The invoked congestion mechanisms; will decrease the network throughput; thus degrading MANET performance [7].Many congestion control exists for TCP. A brief discussion of the TCP variants implemented in this research is discussed in the following sections. Impact of FTP Application file size and TCP Variants on MANET Protocols Performance Abdelmuti Ahmed Abbasher Ali, Dr.Amin Babkir A/Nabi Mustafa