This paper proposes a congestion avoidance mechanism that addresses unicast (TCP or UDP) as well as multicast (UDP) best effort flows. Our mechanism originally combine Explicit Congestion Notification (ECN) based on router active queue management to detect congestion, with ICMP Source Quench messages to inform the involved sources of the network congestion state. The fairness achieved is a trade-off between TCP-like and Max-Min fairness. We demonstrate through simulation that the proposed mechanism enforces fairness and provides an efficient and simple solution to congestion avoidance. Keywords: multicast, active queue management, ICMP source quench, fairness, best effort 1 Introduction In the IP framework, the flows without end-to-end bandwidth guarantees (i.e. best-effort flows) have to adapt efficiently to network dynamics to avoid congestion. Network resources are shared by competing unicast (TCP and UCP) and multicast (UDP) communications. (1) For unicast flows, adaptation is ...

Single-rate reliable multicast protocols are known to have scalability problems in the presence of a large number of receivers because the sender cannot distinguish independent packet losses at different receivers from multiple packet losses at the same receiver. In the presence of a large number of receivers, the sender may perceive a large aggregate packet loss even if no individual receiver is highly congested. Consequently, the multicast session progresses at a much slower rate than its desired sending rate. In order to solve this problem, we argue for decoupling of the mechanisms to achieve congestion control and reliability in reliable multicast protocols, and present a very simple "loss notification" based multicast congestion control mechanism that can be used to augment both ACK-based and NAK-based reliable multicast protocols and solve the independent packet loss problem. We illustrate the efficacy of our approach via simulations using the ns2 simulator. I. INTRODUCTION Re...

Fairness to current Internet traffic, particularly TCP, is an important requirement for new protocols in order to be safely deployed in the Internet. This specifically applies to multicast protocols that should be deployed with great care. In this paper we provide a set of experiments that can be used as a benchmark to evaluate the fairness of multicast congestion control mechanisms when running with competing TCP flows. We carefully select the experiments in such a way to target specific congestion control mechanisms and to reveal the differences between TCP and the proposed multicasting protocol. This enables us to have a better understanding of the proposed protocol behavior and to evaluate its fairness and when violations can happen. To clarify our experiments we carry them on a single-rate case study protocol, pgmcc, using NS-2 simulations. Our analysis shows the strengths and potential problems of the protocol and point to possible improvements. Several congestion control mechanisms are targeted by the experiments such as timeouts, response to ACKs and losses, independent and congestion losses effect. In addition, we evaluate multicast mechanisms such as the effect of multiple receivers, group representative selection, and feedback suppression when there is network support.

Congestion control is a major requirement for multicast to be deployed in the current Internet. Due to the complexity and conflicting tradeoffs, the design and testing of a successful multicast congestion control protocol is difficult. In this paper we present a framework for systematic testing of multicast congestion control protocols based on the STRESS methodology. STRESS has been used to study the correctness and performance of multipoint protocols. Here we extend it to study multicast congestion control, so as to tackle its new semantics and the high complexity of its verification. Our methodology is applied to a single-rate case study protocol and we are able to generate scenarios that can be used for testing multicast congestion control building blocks. Some of the interesting results are the effect of receivers joining and leaving on the throughput measurements, the effect of feedback suppression on congestion control, and the effect of changes in the special receivers representing the group. We hope that this will provide a valuable tool to expedite the development and standardization of such protocols.

Multi-party applications are of great importance, and perhaps the greatest challenge is achieving both a) robustness in the presence of adaptation to dynamic topology and group membership, and b) scalability in terms of bandwidth, state, and processing, as the size of a group grows. Scalable Reliable Multicast (SRM) [1] is a rich example of a robust design intended to work across a wide range of group sizes and dynamic topologies. However, the adaptation mechanisms in SRM rely on shared group state achieved via exchange of session messages. Similar synchronization is important in other multiparty applications and services [2, 3]. Various mechanisms have been proposed to reduce the overhead of this loose group synchronization. This paper uses a self-configuring hierarchy to reduce the overhead of session messages in SRM. Unlike previous proposals, our mechanism uses a stochastic algorithm for self-configuration based on randomized timers and local appropriateness measures. We present in...

Single-rate reliable multicast protocols are known to have scalability problems in the presence of a large number of receivers because the sender cannot distinguish independent packet losses at different receivers from multiple packet losses at the same receiver. In the presence of a large number of receivers, the sender may perceive a large aggregate packet loss even if no individual receiver is highly congested. Consequently, the multicast session progresses at a much slower rate than its desired sending rate. In order to solve this problem, we argue for decoupling of the mechanisms to achieve congestion control and reliability in reliable multicast protocols, and present a very simple "loss notification" based multicast congestion control mechanism that can be used to augment both ACK-based and NAK-based reliable multicast protocols and solve the independent packet loss problem. We illustrate the efficacy of our approach via simulations using the ns2 simulator.