**** Columbia Network Group Seminar ****

Title:    Efforts to Understand Multicast Traffic and Tree Characteristics
Speaker:  Kevin Almeroth (almeroth@cs.ucsb.edu)
          Department of Computer Science
          University of California, Santa Barbara
When:     Wednesday, September 20, 4 pm
Where:    Interschool Lab, CEPSR Building, 7th floor
          Columbia University

Abstract: For some years now, researchers have sought to characterize
          multicast traffic.  The motivations are numerous.  Researchers
          have claimed that for small groups, replicated unicast is
          better.  How small?  Researchers have claimed that Internet
          multicast gives better performance.  According to what metrics
          and how much better?  Researchers have tried to develop
          traffic management services for multicast including
          reliability, congestion control, efficient join/leave
          operations.  But how to test the effectiveness and efficiency
          of these services without an accurate model of multicast trees
          and group dynamics?

          This talk covers the set of research focused on studying and
          characterizing the performance of multicast.  The first half
          of this talk gives a breadth-first presentation of the
          different attempts to understand multicast traffic.  The first
          wave of research covered a variety of topics including traffic
          patterns, loss characteristics, join/leave behavior, and basic
          tree topology information.  This last topic--an understanding
          of topology characteristics--has been the hardest to study and
          the least well understood.  The second half of this talk
          covers a recent paper studying the characteristics of
          multicast tree topologies.  Starting with actual topology data
          collected for a small multicast group, tree characteristics
          including average degree, depth, and degree-at-depth are
          studied.  Then, by relaxing the duration statistics,
          inter-arrival times, source location, and finally group
          composition we study the changing characteristics of multicast
          tree topologies.  Surprisingly, the results show that there is
          a common Internet tree type.  Open questions as a result of
          this research are whether our metrics are sufficient to truly
          capture the nature of multicast trees, and how much will our
          characterization change as the multicast-capable topology
          changes.

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Kevin C.  Almeroth earned his Ph.D.  in Computer Science from the
Georgia Institute of Technology in 1997.  He is currently an assistant
professor at the University of California in Santa Barbara where his
main research interests include computer networks and protocols,
multicast communication, large-scale multimedia systems, and performance
evaluation.  At UCSB, Dr.  Almeroth is a founding member of the Media
Arts and Technology Program (MATP), Associate Director of the Center for
Information Technology and Society (CITS), and on the Executive
Committee for the University of California Digital Media Innovation
(DiMI) program.  In the research community, Dr.  Almeroth is on the
Editorial Board of IEEE Network, is co-chairing the NGC 2000 workshop,
has served as tutorial chair for ICNP 99 and MM 2000, and has been on
the program committee of several conferences.  Dr.  Almeroth is serving
as the chair of the Internet2 Working Group on Multicast, and is a
member of the IETF Multicast Directorate (MADDOGS).

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The seminar is sponsored by the Columbia Network Group, a research group
spanning the Electrical Engineering and Computer Science Departments,
working on topics including optical networking, wireless, middleware,
quality of service, network performance, active networks, and Internet
services.