Multicasting at the IP layer has not been widely adopted due to a combination of technical and non-technical issues. End-system multicast (also called application-layer multicast) is an attractive alternative to IP layer multicast for reasons of user management (set-up and control) and attack avoidance. Sessions can be established on demand such that there are no static points of failure to target in advance. In end-system multicast, an overlay network is built on top of available network

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... es and packets are multicasted at the application layer. The overlay is organized such that each end host participating in a multicast communication re-sends multicasted messages to some of its peers, but not all of them. Thus end-system multicast allows users to manage multicast sessions under varying network conditions without being dependent on specific network conditions or specific network equipment maintaining multicast state information. In this paper we describe a variety of proposed end-system multicast solutions and classify them according to characteristics such as overlay building technique, management, and scalability. Comparing these characteristics across different end-system multicast solutions is a step toward understanding which solutions are appropriate for different battlespace requirements and where further research is needed. * Also referred to as Application layer multicast, application level multicast and overlay multicast.