The Effect of Packet Losses and Delay on TCP Traffic over Wireless Ad Hoc Networks

Abstract

The popularity of wireless network has been growing steadily. Wireless ad hoc networks have been popular because they are very easy to implement without using base stations. The wireless ad hoc networks are complex distributed systems that consist of wireless mobile or static nodes that can freely and dynamically self-organize. The ad hoc networks allow nodes to seamlessly communicate in an area with no pre-existing infrastructure. Future advanced technology of ad hoc network will allow the forming of small ad hoc networks on campuses, during conferences and even in homes. Furthermore, there is an increasing need for easily portable ad hoc networks in rescue mission, especially for accessing rough terrains. However, the quick adaptation and ease of configuration of ad hoc networks come at a price. In wireless ad hoc networks, route changes and network partitions occur frequently due to the unconstrained network topology changes. Moreover, this kind of network inherits the traditional problems of wireless communication, such as unprotected outside signals or interferences, unreliable wireless medium, asymmetric propagation properties of wireless channel, hidden and exposed terminal phenomena, transmission rate limitation and blindly invoking congestion control of transport layer. Although most of these limitations and complexities are due to the lack of fixed backbone or infrastructure, building ad hoc network temporarily is not only simple and easy to implement but also cost-effective and less time-consuming if compared to an infrastructure network that needs to establish a based station and fixed backbone. Among the above mentioned problems and limitations, the impact of transport layer limitations is analyzed across ad hoc routing protocols throughout the network topologies. Transmission Control Protocol (TCP) (Postel, 1981) is the de facto standard designed to provide reliable end-to-end delivery of data packet in the wired networks. Normally, TCP is an independent protocol that is not related to the underlying network technology. However, some assumptions of TCP, such as consideration of only static node, packet losses due to congestion or buffer overflows are inspired from the features of wired networks. In the wireless network, these assumptions may not be correct all the time due to the rapid network topology changes, node movements and limited battery power. In order to apply TCP to an ad hoc environment, TCP has to overcome many problems, such as packet losses due to congestion, high bit errors, node mobility, longer delay and so on. The following TCP