End System Multicast

Abstract: The conventional wisdom has been that Internet protocol (IP) is the natural protocol layer for implementing multicast related functionality. However, more than a decade after its initial proposal, IP multicast is still plagued with concerns pertaining to scalability, network management, deployment, and support for higher layer functionality such as error, flow, and congestion control. We explore an alternative architecture that we term end system multicast, where end systems implement all multicast related functionality including membership management and packet replication. This shifting of multicast support from routers to end systems has the potential to address most problems associated with IP multicast. However, the key concern is the performance penalty associated with such a model. In particular, end system multicast introduces duplicate packets on physical links and incurs larger end-to-end delays than IP multicast. We study these performance concerns in the context of the Narada protocol. In Narada, end systems self-organize into an overlay structure using a fully distributed protocol. Further, end systems attempt to optimize the efficiency of the overlay by adapting to network dynamics and by considering application level performance. We present details of Narada and evaluate it using both simulation and Internet experiments. Our results indicate that the performance penalties are low both from the application and the network perspectives. We believe the potential benefits of transferring multicast functionality from end systems to routers significantly outweigh the performance penalty incurred.

Abstract: In tree-based multicast systems, a relatively small number of interior nodes carry the load of forwarding multicast messages. This works well when the interior nodes are highly-available, dedicated infrastructure routers but it poses a problem for application-level multicast in peer-to-peer systems. SplitStream addresses this problem by striping the content across a forest of interior-node-disjoint multicast trees that distributes the forwarding load among all participating peers. For example, it is possible to construct efficient SplitStream forests in which each peer contributes only as much forwarding bandwidth as it receives. Furthermore, with appropriate content encodings, SplitStream is highly robust to failures because a node failure causes the loss of a single stripe on average. We present the design and implementation of SplitStream and show experimental results obtained on an Internet testbed and via large-scale network simulation. The results show that SplitStream distributes the forwarding load among all peers and can accommodate peers with different bandwidth capacities while imposing low overhead for forest construction and maintenance.

Abstract: The conventional wisdom has been that IP is the natural protocol layer for implementing multicast related functionality. However, ten years after its initial proposal, IP Multicast is still plagued with concerns pertaining to scalability, network management, deployment and support for higher layer functionality such as error, flow and congestion control. In this paper, we explore an alternative architecture for small and sparse groups, where end systems implement all multicast related functionality including membership management and packet replication. We call such a scheme End System Multicast. This shifting of multicast support from routers to end systems has the potential to address most problems associated with IP Multicast. However, the key concern is the performance penalty associated with such a model. In particular, End System Multicast introduces duplicate packets on physical links and incurs larger end-to-end delay than IP Multicast. In this paper, we study this question in the context of the Narada protocol. In Narada, end systems self-organize into an overlay structure using a fully distributed protocol. In addition, Narada attempts to optimize the efficiency of the overlay based on end-to-end measurements. We present details of Narada and evaluate it using both simulation and Internet experiments. Preliminary results are encouraging. In most simulations and Internet experiments, the delay and bandwidth penalty are low. We believe the potential benefits of repartitioning multicast functionality between end systems and routers significantly outweigh the performance penalty incurred.

Abstract: In response to the serious scalability and deployment concerns with IP Multicast, we and other researchers have advocated an alternate architecture for supporting group communication applications over the Internet where all multicast functionality is pushed to the edge. We refer to such an architecture as End System Multicast. While End System Multicast has several potential advantages, a key concern is the performance penalty associated with such a design. While preliminary simulation results conducted in static environments are promising, they have yet to consider the challenging performance requirements of real world applications in a dynamic and heterogeneous Internet environment.In this paper, we explore how Internet environments and application requirements can influence End System Multicast design. We explore these issues in the context of audio and video conferencing: an important class of applications with stringent performance requirements. We conduct an extensive evaluation study of schemes for constructing overlay networks on a wide-area test-bed of about twenty hosts distributed around the Internet. Our results demonstrate that it is important to adapt to both latency and bandwidth while constructing overlays optimized for conferencing applications. Further, when relatively simple techniques are incorporated into current self-organizing protocols to enable dynamic adaptation to latency and bandwidth, the performance benefits are significant. Our results indicate that End System Multicast is a promising architecture for enabling performance-demanding conferencing applications in a dynamic and heterogeneous Internet environment.