Application-Layer Multicast (ALM) is a promising solution to overcome the lack of global IP Multicast support. A common approach is establishing tree-like overlay structures. A multitude of such tree-based protocols exists, each aiming at a single or a small set of application scenarios and following dedicated tree optimization goals. Anyway, most protocols do not offer high configurability and flexibility to support various application cases, nor do they provide means to be sufficiently extensible to also fit upcoming application scenarios. In this paper, a classification of typical functional parts in tree-based ALM protocols is presented. From this insight, a family of tree-based protocols, called MOT-P, is derived, offering high flexibility and extensibility. In MOT-P, the functional parts can be configured separately to use a set of sub-components in order to fit the actual requirements, considerably enhancing flexibility compared to rather monolithic protocol approaches. To support future application scenarios, new sub-components can be created to enhance the protocol's behavior through explicit consideration of such scenarios. Furthermore, MOT-P uses a set of highly configurable heuristics for tree refinement. To show the applicability and flexibility of MOT-P, mappings of existing protocols to MOT-P as well as example ALM scenarios and corresponding protocol configurations are provided.
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