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.

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This study seeks to understand how network failures affect the availability of service delivery across wide area networks and to evaluate classes of techniques for improving end-to-end service availability. Using several large-scale connectivity traces, we develop a model of network unavailability that includes key parameters such as failure location and failure duration. We then use trace-based simulation to evaluate several classes of techniques for coping with network unavailability. We find that caching alone is seldom effective at insulating services from failures but that the combination of mobile extension code and prefetching can improve average unavailability by as much as an order of magnitude for classes of service whose semantics support disconnected operation. We find that routing-based techniques may provide significant improvements, but that the improvements of many individual techniques are limited because they do not address all significant categories of network failures. By combining the techniques we examine, some systems may be able to reduce average unavailability by as much as one or two orders of magnitude.

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In our previous work, 1 we used a simplied model of routing policy in the Internet to study the impact of policy routing on Internet path-lengths. This prior work suered from two shortcomings|it was based on a single snapshot of the Internet topology, and our simplied policy model could generate AS paths that violate peering relationships. In this paper, we address these two shortcomings by re-examining our results with respect to a more recent snapshot of the Internet, and improving the policy model to avoid peering violation. We nd that our prior observations regarding the path ination due to routing policy appear to hold both across time and with respect to a more sophisticated model of routing policy. Keywords: Internet Paths, Paths, Routing Policy, Policy Routing, Path Ination 1.

In this paper, we describe the problems that a ect availability in BGP, such as vulnerability to attacks, slow convergence time, and lack of scalability. These problems arise from the basic assumption of BGP: every router has to cooperate to make routing work. We propose a new routing system, feedback based routing, which bifurcates structural information and dynamic information. Only structural information is propagated. Dynamic information is discovered by the routers based on feedback and probes. Routing decisions are made based on the dynamic information. We argue that this system is resilient to minority compromises in the infrastructure, provides higher availability than BGP, and can scale to the size of the Internet of the future.

Disconnected operation, in which a client accesses a service without relying on network connectivity, is crucial for improving availability, supporting mobility, and providing responsive performance. Because manyweb services are not cachable, disconnected access to web services may require mobile service code to execute in client caches. Unfortunately, (a) this code is untrusted, (b) this code mayhave nearly limitless resource demands due to prefetching, and (c) a large number of competing code modules must coexist. Thus, resource managementisakey problem both for preventing denial of service attacks and for providing good performance across many services. This paper addresses the feasibility of meeting the resource management needs of an environment where service code is shipped to clients, proxies, or content distribution intermediaries. It rst examines the requirements of such a system and then develops a resource-management strategy to meet these requirements by (a) providing isolation across services to prevent denial of service attacks, (b) automatically providing appropriate allocations to dierent services to provide good global performance, and (c) requiring no hand tuning across a wide range of system congurations and workloads. 1.

this paper, we present a more re ned and quanti able understanding of the marginal utility of performing wide-area measurements. We focus on problems in Internet topology discovery, namely, discovering the set of nodes and links which comprise the Internet backbone, discovering the degree distribution of these nodes, and classifying nodes according to their role. We provide a model for how the discovery process scales as the number of measurements and measurement sites increase and validate this model against a set of ########### run across the Internet from 17 measurement sites run to 60,000 destinations. We characterize the topology in terms of nodes, links, node degree distribution, and distribution of end-to-end ows using statistical and information-theoretic techniques

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This thesis presents NATRON, a system in which an overlay network of nodes cooperates to improve unicast routing to non-participating hosts. Previous overlay systems have used overlay routing to improve communication between participating hosts; they were unable to exploit overlay routing to non-participating hosts. NATRON uses a combination of IP tunneling and network address translation to allow members of the overlay to communicate with hosts outside the overlay network via other overlay members. In order to