Abstract — The conventional wisdom has been that 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. In this paper, 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. In this paper, we study these performance concerns in the context of the Narada protocol. In Narada, end systems selforganize 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. I.

While application end-point architectures have proven to be viable solutions for large-scale distributed applications such as distributed computing and file-sharing, there is little known about its feasibility for more bandwidth-demanding applications such as live streaming. Heterogeneity in bandwidth resources and dynamic group membership, inherent properties of application end-points, may adversely affect the construction of a usable and efficient overlay. At large scales, the problems become even more challenging. In this paper, we study one of the most prominent architectural issues in overlay multicast: the feasibility of supporting large-scale groups using an application end-point architecture. We look at three key requirements for feasibility: (i) are there enough resources to construct an overlay, (ii) can a stable and connected overlay be maintained in the presence of group dynamics, and (iii) can an efficient overlay be constructed? Using traces from a large content delivery network, we characterize the behavior of users watching live audio and video streams. We show that in many common real-world scenarios, all three requirements are satisfied. In addition, we evaluate the performance of several design alternatives and show that simple algorithms have the potential to meet these requirements in practice. Overall, our results argue for the feasibility of supporting largescale live streaming using an application end-point architecture.

In this paper, we report on experience in building and deploying an operational Internet broadcast system based on Overlay Multicast. In over a year, the system has been providing a cost-e#ective alternative for Internet broadcast, used by over 3600 users spread across multiple continents in home, academic and commercial environments. Technical conferences and special interest groups are the early adopters. Our experience confirms that Overlay Multicast can be easily deployed and can provide reasonably good application performance. The experience has led us to identify first-order issues that are guiding our future e#orts and are of importance to any Overlay Multicast protocol or system. Our key contributions are (i) enabling a real Overlay Multicast application and strengthening the case for overlays as a viable architecture for enabling group communication applications on the Internet, (ii) the details in engineering and operating a fully functional streaming system, addressing a wide range of real-world issues that are not typically considered in protocol design studies, and (iii) the data, analysis methodology, and experience that we are able to report given our unique standpoint.

Peer-to-peer technologies have proved to be effective for various bandwidth intensive, large scale applications such as file-transfer. For many years, there has been tremendous interest in academic environments for live video streaming as another application of P2P. Recently, a number of new commercial scale video streaming systems have cropped up. These systems differ from others in the type of content that they provide and attract a large number of users from across the globe. These are proprietary systems and very little is known about their architecture and behavior. This study is one of the first of its kind to analyze the performance and characteristics of P2P live streaming applications. In particular, we analyze PPLive and SOPCast, two of the most popular systems in this class. In this paper, we (1) present a framework in which to analyze these P2P applications from a single observable point, (2) analyze control traffic to present a probable operation model and (3) present analysis of resource usage, locality and stability of data distribution. We conclude that P2P live streaming has an even greater impact on network bandwidth utilization and control than P2P file transfer applications.

large-scale distributed network of servers, content distribution, scaleable and reliable algorithm, wide-area testbed, simulation In this work, we consider a large-scale distributed network of servers and a problem of content distribution across it. We propose a novel algorithm, called FastReplica, for an efficient and reliable replication of large files in the Internet environment. There are a few basic ideas exploited in FastReplica. In order to replicate a large file among n nodes (n is in the range of 10-30 nodes), the original file is partitioned into n subfiles of equal size and each subfile is transferred to a different node in the group. After that, each node propagates its subfile to the remaining nodes in the group. Thus instead of the typical replication of an entire file to n nodes by using n Internet paths, connecting the original node to the replication group, FastReplica exploits n x n Internet paths within the replication group where each path is used for transferring 1/n-th of the file. We design a scalable and reliable FastReplica algorithm which can be used for replication of large files to a large group of nodes. The new method is simple and inexpensive. It does not require any changes or modifications to the existing Internet infrastructure, and at the same time, it significantly reduces the file replication time as we demonstrate through experiments on a prototype implementation of FastReplica in a wide-area testbed.

Overlays are an important tool for deploying new services on the Internet. However, the existing overlays are statically configured. For fault tolerance, ease of management, and e#ciency it is crucial that overlays be self-organizing. We present a distributed algorithm to automatically configure the nodes into a logical topology which is dynamic and e#cient. 1

A large number of overlay multicast protocols have been developed, almost all of which assume universal connectivity between end hosts. However, in reality, this assumption is not valid with widespread use of Network Address Translators (NAT) and firewalls. The impact of NAT and firewall connectivity restrictions on overlay multicast, especially in the application-endpoint setting, has not been seriously considered. In this paper, we argue that it is critical to consider connectivity restrictions because NAT and firewall hosts make up a large fraction of the endpoints, affecting proper functionality as well as performance of overlay multicast protocols. We present several design enhancements that explicitly consider connectivity restrictions in overlay multicast and evaluate the design space and tradeoffs based on real Internet broadcasts and Internet testbed experiments.

We use expander graphs to provide efficient new constructions for two security applications: authentication of long digital streams over lossy networks and building scalable, robust overlay networks. Here is a summary of our contributions: (1) To authenticate long digital streams over lossy networks, we provide a construction with a provable lower bound on the ability to authenticate a packet -- and that lower bound is independent of the size of the graph. To achieve this, we present an authentication expander graph with constant degree. (Previous work, such as [MS01], used authentication graphs but required graphs with degree linear in the number of vertices.) (2) To build ecient, robust, and scalable overlay networks, we provide a construction using undirected expander graphs with a provable lower bound on the ability of a broadcast message to successfully reach any receiver. This also gives us a new, more efficient solution to the decentralized certificate revocation problem [WLM00].

Future network intruders will probably use an organized army of malicious nodes (here called “malnodes”, or collectively a “malnet”) to deliver many different attacks, rather than recruiting a disorganized set of compromised nodes per attack. However, partly due to the lack of understanding of the resiliency and efficiency a malnet can have, countering malnets has been ineffective. This paper begins to address this deficiency. Through calculation and simulation for three representative malnets—random, small-world, and Gnutella-like—we show that extremely resilient malnets can be formed to deliver attack code quickly. In particular, we show that disconnecting malnets is possible, but extremely naive approaches such as randomly disinfecting malnodes will not suffice, and effective defenses must either happen very quickly during a second-wave attack, or take effect prior to it. 1.

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