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Modeling the Branching Characteristics and Efficiency Gains in Global Multicast Trees

Modeling the Branching Characteristics and Efficiency Gains in Global Multicast Trees. Robert C. Chalmers and Kevin C. Almeroth UC Santa Barbara, Computer Science {robertc,almeroth}@cs.ucsb.edu http://www.nmsl.cs.ucsb.edu/mwalk Infocom 2001. Goals.

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Modeling the Branching Characteristics and Efficiency Gains in Global Multicast Trees

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  1. Modeling the Branching Characteristics and Efficiency Gains in Global Multicast Trees Robert C. Chalmers and Kevin C. Almeroth UC Santa Barbara, Computer Science {robertc,almeroth}@cs.ucsb.edu http://www.nmsl.cs.ucsb.edu/mwalk Infocom 2001

  2. Goals • goal: to characterize multicast efficiency • efficiency in relation to duplicate unicast streams • goal: to accurately model tree topologies • do inter-domain trees share common properties? • requirement: a clear understanding of the shape of multicast trees web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  3. Key Factors of Shape • height • increase in shared links • breadth • near bottom - sharing • near top - duplication • number of receivers • more likely to share web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  4. Key Factors of Shape • height • increase in shared links • breadth • near bottom - sharing • near top - duplication • number of receivers • more likely to share web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  5. Key Factors of Shape • height • increase in shared links • breadth • near bottom - sharing • near top - duplication • number of receivers • more likely to share web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  6. Key Factors of Shape • height • increase in shared links • breadth • near bottom - sharing • near top - duplication • number of receivers • more likely to share web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  7. Key Factors of Shape • height • increase in shared links • breadth • near bottom - sharing • near top - duplication • number of receivers • more likely to share • branching • where does it occur • how does it affect sharing web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  8. Measuring Efficiency • compare total mcast and ucast hops •  = 1 - Lm / Lu • % gain using mcast • Lm = 18, Lu = 38 •  = 1 - 18 / 38 = .52 • 52% reduction in links traversed (3) (3) (7) (1) (1) (1) (1) (1) (1) (7) (1) (1) (5) (1) (1) (1) (1) (1) web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  9. Estimating Efficiency • expands on work to price mcast (Chuang-98) Lm / Lu = Nk • k  0.8 for a range of generated networks • assuming Lu= Lu / N  = 1 - N • where  = k - 1  0.8 - 1 = -0.2 web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  10. Estimating Efficiency (cont’d) • 20-40 receivers  60-70% improved efficiency • 80% savings for 150 users, 90% for 1,000 web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  11. Efficiency Analysis web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  12. Receiver Duration early clustering 1-minute timeout 20-minute timeout infinite timeout web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  13. Inter-Arrival Times random receiver activity || drops from 0.34 to 0.30 web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  14. Receiver Distribution synthesized group distribution || still lower than for real groups web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  15. Efficiency and Shape • do consistent efficiencies imply similar shapes? • global mcast trees share common properties • long paths from source to backbone • branching in backbone only occurs at a limited number of peering points • long paths from backbone to receiver • the range of tree shapes are constrained by the underlying network connectivity web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  16. Out-degree Frequencies • most nodes have a very low out-degree • result is chains of relay nodes (Pansiot-98) • degree frequencies in Internet routers follow a skewed distribution (Faloutsos-99) web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  17. Average Degree average degree grows with N internal degree tapers off near 1.5 web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  18. Conclusions • accurately characterized mcast efficiency • over a range of receiver dynamics and distributions • useful in effort to deploy multicast • identified common properties of mcast trees • useful to improve tree generation techniques • shape is constrained by network connectivity • http://www.nmsl.cs.ucsb.edu/mwalk • for more information web site - http://www.nmsl.cs.ucsb.edu/mwalk/

  19. Addendum

  20. Unicast vs. Multicast • ratio of ucast to mcast path lengths for 1198 receivers in the SYNTH-1 dataset • majority of mcast paths are 0.7-1.2 times the ucast path length web site - http://www.nmsl.cs.ucsb.edu/mwalk/

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