Chinese Journal of Computers   Full Text
Title	A Survey of the Research on ALM Stability Enhancement
Authors	SU Jin-Shu CAO Ji-Jun ZHANG Bo-Feng
Address	(School of Computer, National University of Defense Technology, Changsha 410073)
Year	2009
Issue	No.3(576—590)
Abstract &   Background	Abstract Due to the increasing popularity of group communication applications in the Internet and the difficulties in deployment of IP multicast, Application Layer Multicast (ALM) begins to attract wide attention. The migration of multicast functions from routers to hosts has the potential to address most problems associated with IP multicast, but also faces with new challenges, such as the stability problem. In this paper, the authors firstly outline the data transmission model, multicast tree construction algorithms and protocol performance criterions of ALM. Then they analyze the reasons for the stability problem in depth and propose the criterion for evaluating the stability of ALM. The authors analyze the influencing factors of the ALM stability, which includes the frequency of node leave, the influencing scope of node leave and the time used to recovery ALM tree. According to the influencing factors, the technologies to enhance the stability of ALM can be classified as reducing the frequency of node leave, reducing the influencing scope of node leave and shortening the time used to recovery ALM tree after node leaves. Based on the classification, all the technologies of stability enhancement were overviewed and compared. And finally, we discuss some possible directions for future research in the area. Keywords multicast; application layer multicast (ALM); stability; influencing factor; survey Background Multicast provides an efficient way for Group communications. It is the key technique to support the next-generation Internet applications. The traditional IP multicast provides multicast mechanism in IP layer. However, the deployment of IP multicast is hampered by lots of unsolved technical problems. Nowadays, Application Layer Multicast (ALM) has attracted lots of attention and become the most alternative to IP multicast. The migration of multicast functions from routers to hosts has the potential to address most problems associated with IP multicast, but also faces with new challenges. In ALM tree, when a parent node quits or fails, all its descendent nodes must adjust their positions, which causes the interruption of multicast connections. This problem is called stability problem of ALM trees, and it may affect the continuity of multicast data transmission and then degrade user experience seriously. Therefore, it is necessary to improve the quality of ALM service by enhancing the stability. How to enhance the stability of ALM is an important research top that we are concerned about. This paper analyzes the reasons for the stability problem in depth and proposes the criterion for evaluating the stability of ALM. The influencing factors of the ALM stability, which includes the frequency of node leave, the influencing scope of node leave and the time used to recovery ALM tree. According to the influencing factors, the technologies to enhance the stability of ALM can be classified as reducing the frequency of node leave, reducing the influencing scope of node leave and shortening the time used to recovery ALM tree after node leaves. Based on the classification, all the technologies of stability enhancement were overviewed and compared. This paper also concludes by indicating some research directions for ALM stability enhancement. We hope this survey will play a fundamental role in exploring the technicality to enhance the stability of ALM. The work is supported by the National Natural Science Foundation of China under grant No.90604006, the National High Technology Research and Development Program(863 Program) of China under grant No.2008AA01A325 and the National Grand Fundamental Research Program(973 Program) of China under grant No.2009CB320503.