Abstract—Wireless ad hoc nodes are freely and dynamically self-organize in communicating with others. Each node can act as host or router. However it actually depends on the capability of nodes in terms of its current power level, signal strength, number of hops, routing protocol, interference and others. In this research, a study was conducted to observe the effect of hops count over different network topologies that contribute to TCP Congestion Control performance degradation. To achieve this objective, a simulation using NS-2 with different topologies have been evaluated. The comparative analysis has been discussed based on standard observation metrics: throughput, delay and packet loss ratio. As a result, there is a relationship between types of topology and hops counts towards the performance of ad hoc network. In future, the extension study will be carried out to investigate the effect of different error rate and background traffic over same topologies. Keywords—NS-2, network topology, network performance, multi-hops I. INTRODUCTION OMMUNICATION in wireless ad hoc mode can be categorized into single hop or multi-hop [1]. In the former mode, no intermediate node whenever it delivers packets as well as not requires any routing protocol. Therefore, the success of communication can still be managed as long as both nodes are in the transmission range of each other [2]. The failure happens when node start moving out of transmission range or weak of signal strength. Meanwhile, in the latter mode which is our attention in this paper involves at least one or more intermediate nodes to transmit packets to a dedicated destination. Normally, the dedicated destination cannot be accessed directly since it is located out of the source node’s transmission range. The following figures illustrate the differences between single hop and multi-hops. In Fig. 1, Node A transmits packet to Node B. In this case, Node B is located in Node A’s transmission coverage. Meanwhile, the opposite situation happens in Fig. 2 where Node C cannot directly communicate with Node A. Haniza N. is with the Faculty of Information and Communication Technology, Universiti Teknikal Malaysia Melaka, 75450 Melaka, Malaysia (phone: 606-331-6574; fax: 606-331-6500; e-mail: haniza@utem.edu.my). Md Khambari, M.N. is with the Faculty of Information and Communication Technology, Universiti Teknikal Malaysia Melaka, 75450 Melaka, Malaysia (e-mail: najwan@utem.edu.my). Shahrin S. is with the Faculty of Information and Communication Technology, Universiti Teknikal Malaysia Melaka, 75450 Melaka, Malaysia (e-mail: shahrinsahib@utem.edu.my). Adib M.Monzer Habbal is with the InterNetWorks Research Group, School of Computing, University Utara Malaysia, 06010 Sintok, Malaysia (e-mail: adib@uum.edu.my). Suhaidi Hassan is with the InterNetWorks Research Group, School of Computing, University Utara Malaysia, 06010 Sintok, Malaysia (e-mail: suhaidi@uum.edu.my). Therefore, Node B is responsible to route packet from Node A to Node C as an alternative. Here, a routing protocol is applied to ensure the logical path of packet delivery is met. Fig. 1a Single hop where two nodes communicates directly within transmission range Fig. 1b Multi-hops (with 2 hops) where a destination node is out of source node's transmission range Based on the functionality of transmission control protocol or TCP, the cycle of packet delivery is considered complete whenever a simple type of packet known as acknowledge (ACK) has been received within sender’s expected duration. If not, a possible network pathology [3] has been occurred which is either packet delay or packet lost. One of the common network actions towards this situation is applying Congestion Control mechanism [4]. For wired network, packet lost is a main indicator of congestion problem and it will invoke sender to adjust their sending rate according to current network traffic situation. However, packet lost in wireless network might come from several causes such as high bit error rate [5], hidden or exposed nodes, power level, signal strength, contention [6], interference [7] and others. The assumption of packet loss caused by congestion will then lead to drastic network performance degradation in wireless environment. Here, we evaluate TCP version likes TCP Tahoe, TCP Reno and Newreno which perform differently in ad hoc network but all still suffer the same problem of inability of distinguish packet loss caused by congestion or wireless channel [1]. In our study, we simulate static ad hoc network in different network topology. The objective of this study is to observe the effects of network topology [8] over multi- hops communication. Therefore, there are three network Topology Influence on TCP Congestion Control Performance in Multi-hop Ad Hoc Wireless Haniza N., Md Khambari, M. N, Shahrin S., Adib M.Monzer Habbal, Suhaidi Hassan C World Academy of Science, Engineering and Technology International Journal of Electronics and Communication Engineering Vol:6, No:1, 2012 61 International Scholarly and Scientific Research & Innovation 6(1) 2012 scholar.waset.org/1307-6892/2986 International Science Index, Electronics and Communication Engineering Vol:6, No:1, 2012 waset.org/Publication/2986