Graduation Semester and Year




Document Type


Degree Name

Doctor of Philosophy in Computer Science


Computer Science and Engineering

First Advisor

Gergely Záruba


Explicit Congestion Notification (ECN) and Active Queue Management (AQM) schemes have been proposed for present-day TCP/IP networks to better manage network congestion. ECN enabled AQMs were shown to have a promising advantage over existing drop-tail queues. However, when implemented, they were susceptible to the following problems: 1) the timeout mechanism or the duration of the reception of three duplicate acknowledgements (ACKs), due to early-dropped packets by these AQMs, delays the response time of TCP (in reducing the offered rate) 2) using ECN with these AQMs has its downsides: i) its messages may get delayed or dropped due to congestion in downstream routers; and ii) TCP implementations at both the source and the destination have to be ECN-compliant (which presents a significant problem in today's cores and end systems); and 3) these AQM schemes, with or without ECN, fail to protect TCP-friendly flows adequately in the presence of non TCP-friendly (e.g., UDP) or malicious flows. This dissertation presents solutions to these problems by proposing two novel AQM modification schemes called Receiver-Window Modification (RWM) and RECHOKe (REpeatedly CHOose and Keep for responsive flows, REpeatedly CHOose and Kill for unresponsive flows). By combining these two schemes with RED, we produce a new AQM scheme called RCUBE (Receiver-Window Modified Random Early Detection queues with RECHOKe). By using RECHOKe as a component, RCUBE easily identifies, controls and punishes malicious flows, by requiring only a small amount of information, approximately proportional to the order of magnitude of malicious flows. By using RWM, we reduce the average TCP queue sizes in the queues and in doing so, not only make it easier to identify malicious flows but also reduce the queuing delay resulting in significant improvements in one-way end-to-end packet delays, delay jitter, throughput and number of dropped packets for TCP-friendly flows. We compare RED, CHOKe, xCHOKe, RECHOKe and RCUBE schemes and show that RCUBE outperforms these schemes in identifying, controlling and punishing malicious flows and in protecting TCP-friendly flows. We also provide a theoretical analysis for RECHOKe, RWM and RCUBE schemes to validate our claims.


Computer Sciences | Physical Sciences and Mathematics


Degree granted by The University of Texas at Arlington