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Performance Evaluation of TCP Vegas Versus Different TCP Variants in Homogeneous and Heterogeneous Networks by Using Network Simulator 2

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Performance Evaluation of TCP Vegas Versus Different TCP Variants in Homogeneous and Heterogeneous Networks by Using Network Simulator 2 International Journal of Electrical & Computer Sciences IJECS-IJENS Vol: 11 No: 03 90 Performance Evaluation of TCP Vegas versus Different TCP Variants in Homogeneous and Heterogeneous Networks by Using Network Simulator 2 First B. S. Yew, Second B. L. Ong, and Third R. B. Ahmad congestion due to packet losses and unusual delay. There is no Abstract— The performances of TCP Vegas versus different algorithm that is designed to minimize the transmission loss as TCP variants in homogeneous and heterogeneous networks were the transmission loss in a wired network is negligible. In evaluated via simulation experiment using network simulator wireless network, the performance of TCP is poor. This is due (ns-2). In our simulation experiments, we investigate the to the transmission losses in the network [3]. The transmission performance of TCP Vegas in both homogeneous and losses in wireless network are not negligible. Transmission heterogeneous wired and wired-cum-wireless networks. In losses in wireless network refer to the high bit error, noise homogeneous wired network, TCP Vegas outperforms other TCP variants. In contrast, the performance of TCP Vegas is the interference and channel errors during the transmission of data worst compared to other TCP variants in homogeneous from the source network to the receiver network. TCP treats wired-cum-wireless network. For both heterogeneous wired the transmission loss as a signal of congestion and invokes its network and heterogeneous wired-cum-wireless network, TCP congestion control. When TCP congestion control responds to Vegas is unable to achieve fair bandwidth allocation when these transmission losses, the assumptions in [2] are violates sharing the bottleneck link with other TCP variants. On the and degrade the end-to-end performance of TCP. other hand, TCP Vegas has a significantly lower delay than other In our research, the performances of TCP Vegas in TCP variants in both homogeneous and heterogeneous wired and wired and wireless network were analyzed. However, instead wireless networks. of implementing TCP Vegas in a purely wireless network that involves the sender and receiver networks as the wireless Index Term— TCP Vegas, Homogeneous, Heterogeneous, environment, we implement wired-cum-wireless network in Wired Network, Wired-cum-Wireless Network. our simulation experiment. The wireless network is chosen as the source (sender) network while the destination (receiver) network is the wired network. We aim to analyze the performance of TCP Vegas as the TCP sender agent in the I. INTRODUCTION wireless network. TCP Vegas is the alternative TCP congestion control algorithm is designed as a mechanism to minimize congestion losses is a wired network [1]. The implementation of TCP congestion control that only involves performances of TCP as a reliable end-to-end data transfer is modification on sending side, proposed by [4].Thus, only the optimizes in wired network due to the implementation of TCP sender network is set to the wireless network while the congestion control algorithm. However, when TCP congestion receiver network is set to wired network with the TCP receiver control algorithm is implemented in wireless network, the agent set to be TCP sink. performance of TCP degrades. The performance of TCP Vegas is compared against In Wired network, congestions in the network occur due other TCP variants. For all TCP variants included TCP Vegas, to packet losses and packet delay. TCP congestion control the performance in wired-cum-wireless network is worst compared to their respective performance in wired network. assumptions in [2] only involve the algorithms to control For TCP Vegas that is implemented in homogeneous network, its performance outperforms other TCP variants in wired network but perform the worst in the wireless network. This is First-B. S. Yew is a student conducting the research on enhancing the performance of TCP Vegas in computer network, University Malaysia Perlis due to the delay estimation scheme of TCP Vegas congestion (e-mail: [email protected]). control algorithm. In wireless network, it is difficult to obtain Second- B. L. Ong is a senior lecturer (PhD) of the Computer and precise delay estimation. Wireless network consist of mobile Communication Engineering Department, University Malaysia Perlis, nodes moving in random direction. These random movements Malaysia. Her research interest includes Wireless Communication, Simulation using ns-2 @ omnett, Mobility Management, Session Initiation Protocol reduce the accuracy of estimation in round trip time and affect (SIP), Cellular Network, IPV6 Network, and Wireless Mesh Network (WMN) the efficiency of TCP Vegas congestion control algorithm in (e-mail: drlynn@ unimap.edu.my). wireless network. The absence of rerouting detection Third-R. B. Ahmad is the dean (PhD, Associate Professor) of the Computer mechanism in TCP Vegas congestion control algorithm also and Communication Engineering Department, University Malaysia Perlis, Malaysia. His research interest includes Computer, Telecommunication and affects its performance in mobile environment. TCP Vegas is Optical Network Modeling, Embedded System Applications Using Single unable to differentiate the increment of delay is due to Board Computer and GNU/Linux (e-mail: [email protected]). 1111403-5656 IJECS-IJENS © June 2011 IJENS I J E N S International Journal of Electrical & Computer Sciences IJECS-IJENS Vol: 11 No: 03 91 rerouting or packet losses and treats all of delay increment as quantifying the joint effect of parameters of automatic repeat packet losses and invokes its congestion control algorithm. As request (ARQ)/ forward error connection (FEC). a result, the sending rate of TCP Vegas is reduces and its K. Pentikousis et. al [10] conduct a survey study on the performance degrades [5]. For TCP Vegas that is implemented performance of the TCP in wired-cum-wireless environments in heterogeneous networks, it is unable to achieve fair From their survey, the present TCP performance-related issues bandwidth allocation in both wired and wireless network. This in wired-cum-wireless environments. They conclude that TCP is mainly due to TCP Vegas proactive congestion control perform poorly in wireless environments in terms of achieved algorithm that tries to prevent incipient congestion by reducing throughput due to the factors of limited bandwidth, Long RTT, its sending rate and resulted in unfair domination of available random losses, short flows, user mobility and power bandwidth [6][7]. consumption. This paper is organized as follows. In section 2, we did H. Balakrishnan et. al [11] compare the mechanisms for literature review on previous works on TCP Vegas improving TCP performance over wireless links. They performances. In section 3, we explain the simulation setup classified these mechanisms into three categories. The first that is used to conduct this simulation experiment using category is the end-to-end protocol, where loss recovery is network simulator (ns-2). The simulation results that are performed by the sender. The second category is the link-layer obtained are discussed in section 4. In section 5, we discuss on protocols that provide local reliability; and the third category the future work of the simulation experiment. Finally, in is the split-connection protocols that break the end-to-end section 6, we conclude on the performances of TCP Vegas on connection into two parts at the base station. These protocols both homogeneous and heterogeneous in wired-cum-wireless shield the wireless transmission losses from the congestion network. losses. II. PREVIOUS WORK III. SIMULATION SETUP L. S. Brakmo et. al [3] had proposed a new technique of The simulation tool used for this simulation experiment is congestion control detection and avoidance called TCP Vegas. ns-2. The simulation environments were divided into two They investigate the performance of TCP Vegas in the wired parts: Homogeneous and heterogeneous wired networks, and network by comparing to the performance of TCP Reno. The Homogeneous and heterogeneous wired-cum-wireless implementation of BSD Unix in the x-kernel based simulator networks. tool is used to analyze the performance of TCP Vegas. From their study, they conclude that TCP Vegas achieves better A. Homogeneous and heterogeneous wired networks throughput. TCP Vegas involves modification to the earlier TCP congestion control algorithm (TCP Tahoe and TCP Reno The network topology used in the simulation [8]) that detects congestion based on packet delay rather than experiment is shown in Fig. 1. The network topology used is a packet loss. The delay estimation scheme is used as a simple dumbbell topology which consists of TCP senders, mechanism to detect the congestion in terms of packet delay. TCP receivers and a pair of routers. The links between the TCP TCP Vegas as the congestion control algorithm optimizes the senders and router 1 are called as the sender links while the performance of TCP due to the implementation of this delay links between the TCP receivers and the router 2 are called the estimation scheme. However, this is only true when TCP receiver links. The sender and receiver link represent a local Vegas is implements in homogeneous wired network. When area network (LAN). The link between router 1 and router 2 is TCP Vegas is implemented in heterogeneous wired network, called the bottleneck link. The bottleneck link represents a TCP Vegas performances become worst. wide area network (WAN). For Homogeneous and A. D. Vendictis et. al [6] evaluate the performance of heterogeneous wired networks, we set four simulation TCP Vegas and TCP Reno behaviors in a heterogeneous wired environments as shown in Table I. network. From their study, they conclude that the fairness of TCP Vegas and TCP Reno cannot be achieved. They had proposed a new TCP congestion control algorithm called TCP NewVegas. TCP NewVegas preserves the excellent features of TCP Vegas in homogeneous wired network and improves the bandwidth fairness of bottleneck link when competing with TCP Reno. R. Dunaytsev et. al [9] evaluate the performance of TCP in wired and wired-cum-wireless networks.
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