A generic late-join service for distributed interactive media

In this paper we present a generic late-join service for distributed interactive media, i.e, networked media which involve user interactions. Examples for distributed interactive media are shared whiteboards, networked computer games and distributed virtual environments. The generic late-join service allows a latecomer to join an ongoing session. This requires that the shared state of the medium is transmitted from the old participants of the session to the latecomer in an efficient and scalable way. In order to be generic and useful for a broad range of distributed interactive media, we have implemented the late-join service based on the Real Time Application Level Protocol for Distributed Interactive Media (RTP/I). All applications which employ this protocol can also use the generic late-join service. Furthermore the late-join service can be adapted to the specific needs of a given application by specifying policies for the late-join process. Applications which do use a different application level protocol than RTP/I may still use the concepts presented in this work. However, they will not be able to profit from our RTP/I based implementation.