This paper proposes a mechanism for equation-based congestion control for unicast traffic. Most best-effort traffic in the current Internet is well-served by the dominant transport protocol, TCP. However, traffic such as best-effort unicast streaming multimedia could find use for a TCP-friendly congestion control mechanism that refrains from reducing the sending rate in half in response to a single packet drop. With our mechanism, the sender explicitly adjusts its sending rate as a function of the measured rate of loss events, where a loss event consists of one or more packets dropped within a single round-trip time. We use both simulations and experiments over the Internet to explore performance. We consider equation-based congestion control a promising avenue of development for congestion control of multicast traffic, and so an additional motivation for this work is to lay a sound basis for the further development of multicast congestion control.

Video Streaming across wide-area networks is one of the most important applications on the Internet. However, most studies of video streaming have been done in theoretical settings instead of practical settings. In this paper, we focus on the quality assurance issue on best-effort networks and propose a practical technique, named staggered two-flow video streaming. We deliver a stored video into two separate flows in a staggered fashion via a VPN pipe from a central server to a proxy server. One containing its essential portion is delivered using a novel controlled TCP, and the other containing its enhanced portion is transmitted using a rate-controlled RTP/UDP. To address the issue of video quality assurance in such a system, we use application-aware approaches to control bandwidth sharing and interactions among flows by exploiting the inherent priority structure of videos, the storage space on proxy servers and the coarse-grain bandwidth assurance of VPN. Our experiments using FreeBSD and simulations on NS2 both have demonstrated the efficacy of the proposed technique. I.

Streaming media transfers over the Internet are expected to behave in a TCP friendly manner and react appropriately to congestion similar to the way TCP does. However, our work shows that existing “TCPfriendly” protocols are not necessarily “media friendly”. In this paper, we present our findings on the impact of the TFRC protocol on streaming media quality. We propose the MARC (Media Aware Rate Control) protocol that, unlike TFRC, exhibits significant tolerance towards transient changes in background workload, while still maintaining TCP-friendliness. 1

I hereby certify that the current thesis is independent work that has not been submitted elsewhere. The presence of voice-over-IP traffic in the Internet is constantly increasing, as it offers improved connectivity and quality-of-service comparable to classical telephony at costs that the rival circuit-switched telephony systems cannot match. This paper evaluates the audio quality of voice-over- IP calls that use the Datagram Congestion Control Protocol (DCCP), a congestion-controlled alternative for the User Datagram Protocol (UDP) that carries most voice-over-IP calls today. A framework for assessing the impact of the transport layer on VoIP streams is presented. The experimental results illustrate some of the problems that the proposed congestion control methods face in preserving the perceived

manifests strong equality towards competing TCP or TCPfriendly flows. Although the RFC 3448 suggests that TFRC is suitable for multimedia, this equality is a great disadvantage in the case of transmitting multimedia over the TFRC. The TFRC emulates TCP-like congestion control using the TCP throughput equation. In the paper, we substitute the TCP throughput equation recommended for the TFRC with a linear throughput equation. Simulation results show that the proposed solution is more suitable for multimedia than the equation proposed in RFC 3448. Experiments were carried out using an event-driven ns-2 simulator, developed in U. C. Berkeley. Index Terms—congestion control, multimedia, TCP-friendly protocol