By: Kai Xu
Advisor: Dr. Nirwan Ansari
Department of Electrical and Computer Engineering

Time: 10:30-11:30 AM, Friday, May 6th, 2005
Place: Room 202, ECE Center, New Jersey Institute of Technology (NJIT), Newark NJ. Directions

Abstract

The transmission control protocol (TCP) exhibits poor performance when used in error-prone wireless networks. Remedy to this problem has been an active research area. However, a widely accepted and adopted solution is yet to emerge. Difficulties of an acceptable solution lie in the areas of compatibility, scalability, computational complexity, and the involvement of intermediate routers and switches.

This dissertation reviews the current start-of-the-art solutions to TCP performance enhancement, and pursues an end-to-end solution framework to the problem. The most noticeable cause of the performance degradation of TCP in wireless networks is the higher packet loss rate as compared to that in traditional wired networks. Loss differentiation techniques have been the most studied area for TCP performance enhancement. Studies conduced by this dissertation research suggest that besides the standard TCP’s inability of discriminating congestion packet losses from losses related to wireless link errors, the standard TCP’s AIMD congestion control algorithm itself needs to be redesigned to achieve better performance in wireless, and particularly, high-speed wireless networks. This dissertation proposes a simple, efficient, and effective end-to-end solution framework that enhances TCP’s performance through techniques of adaptive congestion control and active queue management. By end-to-end, it means a solution with no requirement of routers being “wireless-aware” or “wireless-specific”.

TCP-Jersey has been introduced as an implementation of the proposed solution framework, and its performance metrics have been evaluated through extensive simulations. TCP-Jersey consists of an adaptive congestion control algorithm at the source by means of the source’s achievable rate estimation (ARE) -- an adaptive filter of packet inter-arrival times, a congestion indication algorithm at the queues (i.e., AQM) by means of packet marking, and an effective loss differentiation algorithm at the source by careful examination of the congestion marks carried by the duplicate acknowledgment packets (DUPACK).

Several improvements to the proposed TCP-Jersey have been investigated, including a more robust ARE algorithm, a less computational intensive threshold marking algorithm as the AQM link algorithm, a more stable congestion indication function based on virtual capacity at the link, and performance results have been presented and analyzed via extensive simulations of various network configurations. Stability analysis of the proposed ARE algorithm has been conducted and the analytical results have been verified by simulations. Performance of TCP-Jersey has been compared to that of a “perfect”, but not practical, TCP scheme, and encouraging results have been observed. Finally, the framework of the TCP-Jersey’s source algorithm has been extended and generalized for rate-based congestion control, as apposed to TCP’s window-based congestion control, to provide a design platform for applications, such as real-time multimedia, that do not use TCP as the transport protocol and yet do need to control network congestion as well as combat packet losses in wireless networks.

In conclusion, the framework presented in this dissertation that combines the adaptive congestion control and active queue management in solving the TCP performance degradation problem in wireless networks has been shown as a promising answer to the problem due to its simplistic design philosophy, complete compatibility with the current TCP/IP and AQM practice, end-to-end architecture for scalability, and the high effectiveness and low computational overhead.

Committee Members:

Dr. Nirwan Ansari, Prof. of ECE, NJIT (Advisor/Chair)
Dr. Sirin Tekinay, Associate Prof. of ECE, NJIT
Dr. Mengchu Zhou, Prof. of ECE, NJIT
Dr. Yun-qing Shi, Prof. of ECE, NJIT
Dr. Cristian M. Borcea, Assistant Prof. of CS, NJIT