Modified freeze-TCP for improved performance in mobile wireless networks

Abstract

With the rapid development of wireless network technologies, such as cellular networks, the demand for wireless data access is becoming a reality. Third-generation (3G) technologies are set to enter the market in the very near future, allowing increased bandwidth and marking a shift from the circuit-switch mode characteristics of first and second-generation cellular networks to packet mode operation. Future wireless networks (such as a future 4G cellular system) are expected therefore to move towards an all-IP network, so that wireless networks become a part of the global Internet. Such an all-IP network has the potential to provide cost savings through simplified integration among different networks and enhanced service capabilities to a wide base of consumers. Given the wide deployment of the Transmission Control Protocol (TCP) as the Transport Layer protocol in wired networks and the desire to allow internetworking between wired and wireless networks with minimal intervention from intermediate nodes, so that information can be accessed at any time without incurring major changes in existing infrastructure or disruption in performance, it makes sense to use TCP not only in the wired Internet but also in the wireless network. However, TCP is based on assumptions that are not valid in wireless environments, which leads to poor performance in wired-wireless networks. TCP performance problems exist not only due to the wireless channel characteristics but also due to mobility in cellular-based networks, as the mobile host (MH) hands off from one cell coverage area to the next. A considerable effort has been made in recent years to modify TCP for wireless and mobile environments. The protocol behaviour dependence on the particular packet loss characteristics (e.g. short duration vs long duration) and frequency of losses encountered makes the solutions studied to be targeted to the characteristics of a particular environment. Furthermore, the underlying network characteristics call for different approaches to be used depending on the level of support that can be obtained from the components of the network and its characteristics. Some works have shown that the TCP performance degradation is particularly serious in cases where a connection is lost for extended periods. Although a broader discussion of TCP performance problems and solutions is presented, it is on this specific type of problem that we focus our attention in this thesis.