Abstract — This paper describes Scalable Reliable Multicast (SRM), a reliable multicast framework for light-weight sessions and application level framing. The algorithms of this framework are efficient, robust, and scale well to both very large networks and very large sessions. The SRM framework has been prototyped in wb, a distributed whiteboard application, which has been used on a global scale with sessions ranging from a few to a few hundred participants. The paper describes the principles that have guided the SRM design, including the IP multicast group delivery model, an end-to-end, receiver-based model of reliability, and the application level framing protocol model. As with unicast communications, the performance of a reliable multicast delivery algorithm depends on the underlying topology and operational environment. We investigate that dependence via analysis and simulation, and demonstrate an adaptive algorithm that uses the results of previous loss recovery events to adapt the control parameters used for future loss recovery. With the adaptive algorithm, our reliable multicast delivery algorithm provides good performance over a wide range of underlying topologies. Index Terms—Computer networks, computer network performance, Internetworking.

The ability to share synchronized views of interactions with an application is critical to supporting synchronous collaboration. This paper suggests a simple synchronous collaboration paradigm in which the sharing of the views of user/application interactions occurs at the window level within a multi-user, multi-window application. The paradigm is incorporated in a toolkit, DistView, that allows some of the application windows to be shared at a fine-level of granularity, while still allowing other application windows to be private. The toolkit is intended for supporting synchronous collaboration over wide-area networks. To keep bandwidth requirements and interactive response time low in such networks, DistView uses an object-level replication scheme, in which the application and interface objects that need to be shared among users are replicated. We discuss the design of DistVlew and present our preliminary experience with a prototype version of the system.

Several reliable multicast protocols have been proposed, much as TCP is a generic transport protocol for reliable unicast transmission. Unfortunately, most of the solutions are designed for specific applications and do not scale well to either network size or group size. This paper is intended to propose a framework for applications which require reliable multicast support. It only provides minimum reliable data delivery support and leaves semantics and flexibility to applications themselves as much as possible. Generally speaking, a reliable data delivery protocol requires an error recovery mechanism and a congestion control mechanism. Unlike the traditional unicast scenario where only a single sender and a single receiver are involved, there are multiple senders and multiple receivers in a multicast group. This special characteristic of multicast environments introduces new challenges in solving error recovery and congestion control. Our goal is to design a reliable multicast protocol which provides services with high scalability and low cost. We start with a receiver-initiated reliable delivery model and investigate error recovery mechanisms to improve the efficiency, hence the scalability. Our future research direction will explore congestion control in multicast environments. Contents 1

of the Dissertation Competitive Execution in a Distributed Environment by Sung Hyun Cho Doctor of Philosophy in Computer Science University of California, Los Angeles, 1996 Professor David R. Jefferson, Chair We propose an alternative to process migration, called competition, to speed up distributed programs in the background on a network of variable-speed processors. Competition protocols are transparent operating system facilities that involve creating multiple instances (called clones) p 1 , p 2 , etc. of a process P on different variable-speed processors, and making clones "compete", i.e., attempting to guarantee that the output of the clone that is farthest "ahead" is fed to the rest of the computation, and that the entire application's performance tracks that of the clone which is farthest ahead. One clone may be ahead of or behind others depending on the current foreground loads. If for any reason there is variation in the progress of the clones, so that one clone is ahead at ...

and implementation of a secure wide-area object middleware