近幾年來，研究人員利用CBT(Core Based Tree)，PIM(Protocol Independent Protocol)等通訊協定在網際網路上傳遞群播(Multicast)資料。過去所提出的設置中心點(Core)方法基本上需要完整的網路拓撲資訊，然而分散式網路(如網際網路)往往無法滿足這種需求。因此研究人員提出分散式的設置中心點方法解決此問題。雖然分散式的方法不再需要完整的網路拓撲資訊，但是當遷徙中心點時，仍需要群組成員(Member)的資訊作為評估的依據找出中心點的最佳位置，使得群播更有效率。
在這篇論文中，我們設計一個在大型動態群播樹上的分散式通訊協定(Scalable Core Migration Protocol, 簡稱SCMP)，當群播樹擴張或縮減時，可遷徙中心點至近乎最佳的位置，並且能有效率的遷徙。在我們的通訊協定中，所有群組成員的資訊被分散至區域的代理人(Agent)，而中心點只需要維護這群代理人的資訊；並且我們只需從這群代理人中挑選一個最佳者作為中心點。因而，當遷徙中心點時，我們所提出的方法降低了所花費的時間(Runtime Overhead)及花費的訊息(Message Overhead)。

Over the year, researchers have proposed the core based trees (CBT) and protocol independent multicasting (PIM) protocols to route multicast data on Internet. Some previously proposed heuristics for locating the Core of a group typically require knowledge of the complete network topology, a requirement that is not always practical for a distributed problem such as Internet routing. Recently, many researchers have proposed distributed algorithms for locating the Core of a group. Although knowledge of the network topology is not explicitly assumed, some knowledge such as information of sources/members is necessary for computing the metric such as average tree cost or maximum end-to-end delay to find the best location of the group's Core such that multicasting efficiently.
We proposed a scalable distributed protocol that can be used to migrate Core to near-optimal location for dynamic multicast tree, and allow the Core to migrate efficiently when the multicast tree is expanded or shrunken. In our protocol, information of overall members is distributed among local Agents; the Core only maintains information of Agents of the group. Also, only the Agents participate Core selection. Therefore, the proposed protocol reduces the runtime overhead and message overhead while computing Core migration.

[AK98] S. Ali and A. Khokhar, “Distributed Center Location Algorithm for Fault-Tolerant Multicast in Wide-Area Networks”, Reliable Distributed Systems, Proc. 17th IEEE Symposium, 1998, pp. 324-329.
[BCF97] T. Billhartz, J.B. Cain, and E.F. Goudreau, " Performance and Resource Cost Comparisons for the CBT and PIM Multicast Routing Protocols", Select. Areas in Commun., IEEE Journal on Vol. 15, No. 3, Apr. 1997, pp. 304-315.
[BFC93] A.J. Ballardie, P.F. Francis, and J. Crowcroft, “Core Based Trees”, Proc. ACM SIGCOMM, Sept. 1993, pp. 85-95.
[CZD95] K.L. Calvert, E.W. Zegura, and M.J. Donahoo, “Core Selection Methods for Multicast Routing”, Proc. 4th ICCCN, IEEE, Sept. 1995, pp. 638-642.
[DEFJLW96] S. Deering, D.L. Estrin, D. Farinacci, V. Jacobson, C. -G. Liu, and L. Wei, “The PIM Architecture for Wide-Area Multicast Routing”, Networking, IEEE/ACM Transactions on Vol. 4, No. 2, Apr. 1996, pp. 153-162.
[DJEFMWH97] S. Deering, V. Jacobson, D. L. Estrin, D. Farinacci, D. Meyer, L. Wei, and A. Helmey, “Protocol Independent Multicast – Dense Mode (v2): Specification”, Internet Draft, Aug. 1997.
[DZ96] M.J. Donahoo and E.W. Zegura, "Core migration for dynamic multicast routing", Proc. 5th ICCCN, IEEE, Oct. 1996, pp. 92-98.
[EHHH99] D. Estrin, M. Handley, A. Helmy, and P. Huang, "A Dynamic Bootstrap Mechanism for Rendezvous-based Multicast Routing", INFOCOM '99. 9th Annual Joint Conference of the IEEE Computer and Communications Societies, Proc. IEEE, March 1999, pp. 1090-1098.
[FHM98] E. Fleury, Y. Huang, and P.K. McKinley, "On the Performance and feasibility of Multicast Core Selection Heuristics", Proc. 7th ICCCN, IEEE, Oct. 1998, pp. 296-303.
[GJ88] M.R. Garey and D.S. Johnson, Computers and Intractability: A Guide to the Theory of NP-Completeness. New York: Freeman, June 1988.
[GR99] A. Gulati and S. Rai, "Core Discovery in Internet Multicast Routing Protocol", Performance, Computing and Communications Conference, 1999 IEEE International, Feb. 1999, pp. 143-149.
[HFM] Y. Huang, E. Fleury, and P.K. McKinley, "LCM: A Multicast Core Management Protocol for Link-State Routing Networks", Proc. ICC, IEEE, 1998, pp. 1197-1201.
[KP99] W.T. Kim and Y.J. Park, "DCBT: An Efficient Multicast Architecture for Wide scale and Large Group Multimedia Communications", Proc. ICC, IEEE, June 1999, pp. 665-670.
[LL98] H.C. Lin and SC Lai, "Core Placement for the Core Based Tree Multicast Routing Architecture", Global Telecommunications Conference, GLOBECOM IEEE, Nov. 1998, pp. 1049-1053.
[LLS98] C. Liu, M.J. Lee, and T.N. Saadawi, “Core-Manager Based Scalable Multicast Routing”, Proc. ICC, IEEE, June 1998, pp. 436-441.
[M94] J. Moy, “Multicast Extensions to OSPF”, Technical Report RFC 1584, Network Working Group, Mar. 1994.
[P98] T. Pusateri, “Distance Vector Multicast Routing Protocol”, Internet Draft, Mar. 1998.
[PG95] M. Parsa and J.J. Garcia-Luna-Aceves, "Scalable Internet Multicast Routing", Proc. 4th ICCCN, IEEE, Sept. 1995, pp. 162-166.
[RB97] G.N. Rouskas and I. Baldine, "Multicast Routing with End-to-End Delay and Delay Variation Constraints", Select. Areas in Commun., IEEE Journal on Vol. 15, No. 3, Apr. 1997, pp. 346-356.
[RMH99] J. Reeve, P. Mars, and T. Hodgkinson, "Learning Algorithms for Multicast Routing", Communications, IEE Proceedings, Vol. 146, No.2, April 1999, pp. 89 -94.
[SBK94] S.B. Shukla, E.B. Boyer, and J.E. Klinker, "Multicast tree construction in network topologies with asymmetric link loads", Naval Postgraduate School, Tech. Rep. NPS-EC-94-012, Sept. 1994.
[SG97] C. Shields and J.J. Garcia-Luna-Aceves, "The Ordered Core Based Tree Protocol", INFOCOM '97, 6th Annual Joint Conference of the IEEE Computer and Communications Societies, 1997, pp. 884-891.
[TR97] D.G. Thaler and C.V. Ravishankar, “Distributed Center-Location Algorithms”, Select. Areas in Commun., IEEE Journal on Vol. 15, No. 3, Apr. 1997, pp. 291-303.
[VBS95] R. Voigt, R. Barton, and S.B. Shukla, "A tool for configuring multicast data distribution over global networks", Proc. INET, 1995, pp. 455-463.
[W80] D.W. Wall, "Mechanisms for broadcast and selective broadcast", Ph.D. Dissertation, Stanford University, June 1980.
[W88] B. M. Waxman, "Routing of multipoint connections", Select. Areas in Commun., IEEE Journal on Vol. SAC-6, Dec. 1988, pp. 1617-1622.
[WE93] L. Wei and D. Estrin, "A comparison of multicast trees and algorithms", Comput. Sci. Dept., Univ. Southern California, Tech. Rep. USC-CS-95-560, Sept. 1993.