One of the challenges in reliable multicast is approximating or replicating TCP's congestion control algorithm. This has led to various proposals to adapt TCP itself for use over multicast. The drawback of these multicast TCP services is that they place significant processing load on the sender and they fail to deal with the problem of ACK implosion. This paper shows how concast, a network-layer aggregation service, can be used in conjunction with a standard (unmodified) TCP implementation to support reliable multicast while avoiding ACK implosion and offloading ACK processing. Our prototype implementation shows that, even for relatively small groups, distributing the ACK processing and reducing ACK losses translates into significant improvements in end-to-end transmission rates.

Abstract Multicast services have been used to transmit multimedia data to large receiver groups. Only recently have counterpart network services been introduced to provide similar scalability and anonymity in the opposite direction (i.e. messages from a group of senders destined for a common receiver). In this paper, we explore how these many‐to‐one services, specifically the concast service, can be used to improve the scalability and performance of multimedia applications. In particular, we show how such services can be used in both the control and data planes to overcome well‐known scalability problems (e.g. with Real Time Protocol) that are difficult to solve effectively with end‐system approaches alone. We validate our solutions by presenting experimental results taken from prototype video and audio applications we designed and implemented. Our initial results show substantial reductions in congestion‐induced loss using these generic services. Copyright © 2003 John Wiley & Sons, Ltd.

Multicast services have been used for many years to transmit multimedia data to large receiver groups. However, only recently have counterpart network services been introduced that provide similar scalability and anonymity in the opposite direction (i.e., messages from a group of senders destined for a common receiver). In this paper, we explore how these emerging services, specifically a concast service (many-to-one communication service), can be used to improve the scalability and performance of multimedia applications. In particular, we show how such services can be used in both the control and data planes to overcome well-known scalability problems (e.g., with RTP) that are difficult to solve effectively with end-system approaches alone. We validate our solutions by presenting experimental results taken from prototype video and audio applications we designed and implemented. Our initial results show a reduction of as much as two orders of magnitude in packet loss rates using these generic services.

Concast is a network layer service that provides many-to-one channels: multiple sources send messages toward one destination, and the network delivers a single "merged" copy to that destination. As we have defined it, the service is generic but the relationship between the sent and received messages can be customized for particular applications. We describe the concast service and show how it can be implemented in a back ward-compatible manner in the Internet. We describe its use to solve a problem that has eluded scalable end-system-only solutions: collecting feedback in multicast applications. Our preliminary analysis of concasting effectiveness shows that it provides significant benefits, even with partial deployment. We argue that concast has the characteristics needed for a programmable service to be widely accepted and deployed in the Internet.