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End System Multicast
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A wide range of group communication applications such as audio and
video conferencing, multi-party Internet games, and distance
learning are emerging today. Efficient network support for
multi-point communication is a key requirement for the wide-spread
deployment of these applications. 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 project, we explore an alternative architecture 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. Yet, several issues need to be
resolved before End System Multicast becomes a practical alternative
to IP Multicast. We are studying these issues in the context of a
protocol that we have developed: Narada. In Narada, end systems
self-organize into an overlay using a fully distributed protocol,
and optimize the efficiency of the overlay by considering
application performance and adapting to network dynamics.
To demonstrate the feasibility of the End System
Multicast architecture, we are broadcasting
the ACM SIGCOMM Conference to be held in Pittsburgh between
August 21-23, 2002 using End System Multicast.
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Global Network Positioning (GNP)
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Achieving high performance in peer-to-peer overlay applications in a
scalable fashion is a challenging problem. Simple approaches that try
to measure peer-to-peer network performance by brute force can be
prohibitively expensive. In addition, many overlay algorithms require
the peer-to-peer performance characteristics to be mapped onto a
mathematical structure. Global Network Positioning (GNP) is a solution
that can transform the complex peer-to-peer round-trip time
relationships in the Internet into a simple geometric space structure
(e.g. an N-dimensional Euclidean space). In this structure, each peer
is characterized by a set of geometric coordinates that indicate its
position. We have found through extensive Internet experiments that
the geometric distances between peers in the GNP structure can
accurately approximate the actual Internet network round-trip
times. Thus the GNP structure can provide an accurate means for
predicting Internet round-trip times, and provide a topologically
sensitive mathematical structure for many overlay applications.
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Peer-to-Peer Content Distribution
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Content distribution on the Internet uses many different service
architectures, ranging from centralized client-server to fully
distributed. Compared to centralized schemes, fully distributed
peer-to-peer content distribution provides more resilience and higher
availability through wide-scale replication of content at large
numbers of peers. However, wide-scale replication introduces many new
challenges in locating and retrieving content. We design our content
distribution system to deal with scale, heterogeneity and dynamic
performance.
We are involved in several ongoing projects that study different
flavors of peer-to-peer content distribution. We explore the use of a
simple, yet powerful observation called interest-based locality
to provide scalable and high-performance content lookups and
retrievals in peer-to-peer systems. We are also studying how to scale
Gnutella, a popular file-sharing application. And, we are studying how
selective use of peer-to-peer communications can enhance existing
client-server systems in the CoopNet project.
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