目前許多大型的伺服器都架構在點對點的分散式系統上以避免集中管理的設計及增加可擴充性(scalability)。傳統的點對點通訊協定通常都是利用二元樹(binomial-tree)來達到減少路線的長度。這樣的通訊協定當有熱門資料點存在時，卻反而會造成網路阻塞。這篇論文中，我們提供了一套能數量化(scalable)且均衡負載(load-balanced)的點對點通訊協定，稱之為SCALLOP。
我們的通訊協定利用平衡樹(balanced-tree)來均勻分布網路流量，而減少或去除網路壅塞的問題。在有N台機器系統中建立SCALLOP，只需要每台機器儲存另外log(N)台機器的資訊，因此可達到數量化。除此之外，SCALLOP提供有效的自我管理機制去處理系統中機器動態的加入、離開或失靈。
我們做了一系列的實驗去比較SCALLOP和另一個採用二元樹且被廣泛利用討論的通訊協定Chord。實驗結果顯示SCALLOP成功的利用平衡樹將網路負載均勻分布並避免網路壅塞點。而且它的可自定性能進一步減短網路路徑及網路傳輸量。

Many large-scaled servers are implemented as a peer-to-peer (P2P) distributed system to avoid centralized management and increase scalability. Traditional P2P lookup protocols often utilize binomial lookup trees to shorten lookup paths.
Such a lookup protocol introduces routing bottlenecks when certain nodes become hot spots. In this paper, we present a scalable and load-balanced P2P lookup protocol called SCALLOP. This protocol utilizes balanced lookup trees to evenly distribute routing traffic among nodes and, therefore, reduce or eliminate the occurrence of routing bottlenecks. SCALLOP achieves scalability by storing in each node O(log N) routing information in an N-node distributed system. Furthermore, a self-organized mechanism is proposed to efficiently recover a system when nodes join, leave, and fail dynamically. We conduct a series of experiments to compare SCALLOP and Chord, the most-referenced and representative binomial lookup protocol.
The experimental results show that, with balanced lookup trees, SCALLOP delivers more balanced routing loads and avoids routing bottlenecks. In addition, its customizable feature reduces lookup paths and the total number of routed requests at the cost of larger lookup tables.

[1] W. J. Bolosky, J. R. Douceur, D. Ely, and M. Theimer. Feasibility of a Serverless Distributed File System Deployed on an Existing Set of Desktop PCs. In Proceedings of ACM SIGMETRICS, pages 34-43, June 2000.
[2] Jerry C. Y. Chou, Tai-Yi Huang, and Kuang-Li Huang. SCALLOP: A Scalable and Load-Balanced Peer-to-Peer Lookup Protocol for High-Performance Distributed System. In 4th IEEE/ACM International Symposium on Cluster Computing and the Grid (CCGrid), April 2004.
[3] Ian Clarke, Oskar Sandberg, Brandon Wiley, and Theodore W. Hong. Freenet: A Distributed Anonymous Information Storage and Retrieval System. Lecture Notes in Computer Science, 2009:46-66, 2001.
[4] A. Fiat and J. Saia. Censorship Resistant Peer-to-Peer Content Addressable Networks. In Proceedings of Symposium on Discrete Algorithms, pages 94-103, 2002.
[5] Pierre Fraigniaud and Philippe Gauron. An Overview of the Content-Addressable Network D2B. In Proceedings of the 23nd Annual ACM Symposium on Principles of Distributed Computing (PODC), July 2003.
[6] Frank Dabek and M. Frans Kaashoek and David Karger and Robert Morris and Ion Stoica. Wide-area cooperative storage with CFS. In Proceedings of the 18th ACM Symposium on Operating Systems Principles (SOSP), pages 202-215, Chateau Lake Louise, Banff, Canada, October 2001.
[7] Gnutella. http://gnutella.wego.com/.
[8] Steven Hazel and Brandon Wiley. AChord: A Variant of the Chord Lookup Service for Use in Censorship Resistant Peer-to-Peer Publishing Systems. In Proceedings of International Workshop on Peer-to-Peer Systems (IPTPS), March 2002.
[9] M. Frans Kaashoek and David R. Karger. Koorde: A Simple Degree-Optimal Distributed Hash Table. In Proceedings of International Workshop on Peer-to-Peer Systems (IPTPS), February 2003.
[10] D. Karger, E. Lehman, T. Leighton, M. Levine, D. Lewin, and R. Panigrahy. Consistent Hashing and Random Trees: Distributed Caching Protocols for Relieving Hot Spots on the World Wide Web. In ACM Symposium on Theory of Computing, pages 654-663, May 1997.
[11] KaZaA. KaZaA file sharing network. In http://www.kazaa.com/,2002.
[12] J. Kubiatowicz, D. Bindel, Y. Chen, P. Eaton, D. Geels, R. Gummadi, S. Rhea, H. Weatherspoon, W. Weimer, C. Wells, and B. Zhao. OceanStore: An Architecture for Global-scale Persistent Storage. In Proceedings of the 9th international Conference on Architectural Support for Programming Languages and Operating Systems (ASPLOS), pages 190-201. ACM, November 2000.
[13] Abhishek Kumar, Shashidhar Merugu, Jun Xu, and Xingxing Yu. Ulysses: A Robust, Low-Dimeter, Low-Latency Peer-to-Peer Network. In Proceedings of the 11th IEEE International Conference on Network Protocols, pages 258-267, November 2003.
[14] K. Laskshminaraynan, A. R. Rao, S. Surana, R. Karp, and I. Stoica. Hyperchord: A Peer-to-Peer Data Location Architecture. Technical Report CS-021208, U.C. Berkeley, December 2001.
[15] Dahlia Malkhi, Moni Naor, and David Ratajczak. Viceroy: A Scalable and Dynamic Emulation of the Butter°y. In Proceedings of the 21nd Annual ACM Symposium on Principles of Distributed Computing (PODC), pages 183{192, July 2002.
[16] Morpheus. Morpheus file sharing network. In http://www.musiccity.com/,2002.
[17] M. Naor and U. Wieder. A Simple Fault Tolerant Distributed Hash Table. In Proceedings of International Workshop on Peer-to-Peer Systems (IPTPS), February 2003.
[18] Napster. http://www.napster.com/.
[19] G. Pandurangan. Building Low-Diameter P2P Networks. In Proceedings of the 42nd IEEE Symposium on Foundations of Computer Science, pages 492-499, 2001.
[20] C. G. Plaxton, R. Rajaraman, and A. W. Richa. Accessing Nearby Copies of Replicated Objects in a Distributed Environment. In ACM Symposium on Parallel Algorithms and Architectures, pages 311-320, 1997.
[21] S. Ratnasamy, P. Francis, M. Handley, R. Karp, and S. Shenker. A Scalable Content Addressable Network. In Proceedings of ACM SIGCOMM Conference, pages 161-172, August 2001.
[22] A. Rowstron and P. Druschel. Pastry: Scalable, Decentralized Object Location, and Routing for Large-Scale Peer-to-Peer Systems. Lecture Notes in Computer Science, 2218:329-340, 2001.
[23] Jared Saia, Amos Fiat, Steven D. Gribble, Anna R. Karlin, and Stefan Saroiu. Dynamically Fault-Tolerant Content Addressable Networks. In Proceedings of International Workshop on Peer-to-Peer Systems (IPTPS), March 2002.
[24] I. Stoica, R. Morris, D. Karger, F. Kaashoek, and H. Balakrishnan.
Chord: A Scalable Peer-to-Peer Lookup Service for Internet Applications. In Proceedings of ACM SIGCOMM Conference, pages 149-160, September 2001.
[25] I. Stoica, R. Morris, D. Karger, F. Kaashoek, and H. Balakrishnan. Chord: A Scalable Peer-to-Peer Lookup Service for Internet Applications. Technical Report TR-819, MIT LCS, March 2001.
[26] C. A. Thekkath, T. Mann, and E. K. Lee. Frangipani: A Scalable Distributed File System. In ACM Symposium on Operating Systems Principles (SOSP), pages 224{237, October 1997.
[27] Marc Waldman, Aviel D. Rubin, and Lorrie Faith Cranor. Publius: A Robust, Tamper-Evident, Censorship-Resistant, Web Publishing System . In Proceedings of the 9th USENIX Security Symposium, pages 59{72, August 2000.
[28] J. Xu. On the Fundamental of Tradeo®s between Routing Table Size and Network Diameter in Peer-to-Peer Networks. In Proceedings of IEEE Infocom Conference, pages 151{163, January 2003.
[29] B. Y. Zhao, Ling Huang, J. Stribling, S.C. Rhea, A.D. Joseph, and J.D. Kubiatowicz. Tapestry: A Resilient Global-scale Overlay for Service Deployment. IEEE Journal on Selected Areas in Communications, 22(1):41{53, January 2003.
[30] B. Y. Zhao, J. D. Kubiatowicz, and A. D. Joseph. Tapestry: An Infrastructure for Fault-tolerant Wide-area Location and Routing. Technical Report UCB/CSD-01-1141, U.C. Berkeley, April 2001.