TCP Adaptation Schemes in Heterogeneous and Ad Hoc Wireless Networks

This dissertation, "TCP Adaptation Schemes in Heterogeneous and Ad Hoc Wireless Networks" by Zhi, Li, 李志, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled TCP Adaptation Schemes in Heterogeneous and Ad Hoc Wireless Networks submitted by Zhi LI for the degree of Doctor of Philosophy at The University of Hong Kong August 31 2005 TCP (Transmission Control Protocol) has extended its reach to the wireless realm, and is widely used in all sorts of wireless environments. However, severe performance degradation results when TCP is used over a wireless link. The main reason is the assumption in TCP, i.e., congestion is the primary reason for packet losses. Although a large number of wireless TCP adaptation schemes have been proposed in the literature, improving TCP performance is still very much unexplored in wireless environments. Traditionally, various enhancements to the TCP have been evaluated based on an unrealistic channel model-two-state (good or bad) link. We incorporate into our NS-2 based simulation platform a realistic channel model with an adaptive physical layer that exploits the continuously time-varying channel quality (instead of just two states) to compare several well-known TCP al- gorithms in a homogeneous/heterogeneous wireless network. Our results indicate that even re- portedly inferior wireless TCP approaches can utilize the varying channel conditions to generate better performance. Furthermore, we propose a new explicit congestion control strategy called differentiated marking (DM). DM works by using a two-way approach to further reduce the time required for the sender and the receiver to note the congestion problem, possibly induced by too heavy traffic or burst errors caused by the time-varying channel quality. Mobility is an important characteristic of the mobile nodes in multihop ad hoc wireless net- works. Much research has been done on designing ad hoc routing protocols, principally in order to solve the problem of route failure for mobility. However, the modification of TCP is needed at least for the communication end points. In view of this drawback, we propose a routing protocol called local route recovery (LR) to solve this problem. In our proposed algorithm, since route breakage is found locally, the remedial work should be done locally. Thus, the route error is shielded from the TCP sender and, as such, no TCP modification is needed. Extensive simulations using the NS-2 platform have demonstrated that LR outperforms several well-known algorithms, such as DSR, AODV and ELFN. A number of effective security mechanisms have been used in the Internet. However, these methods are not fully applicable in mobile ad hoc wireless networks due to the features of in- frastructureless, dynamic topology and self-organization. We propose a data multipath routing algorithm called Multipath TCP Security (MTS) to enhance data security. In MTS, the source node adaptively chooses the available routes rather than exhaustively testing the "stored routes"one by one. Simulation results show that MTS provides a reasonably good level of security and performance. (Total words: 421) DOI: 10.5353/th_b3203732 Subjects: TCP/IP (Computer network protocol) Wireless communication systems