Configuration of ACK trees for multicast transport protocols

For scalable multicast transport, one of the promising approaches is to emp loy a control tree known as acknowledgement (ACK) tree which can be used to convey information on reliability and session status from receivers to a r oot sender. The existing tree configuration has focused on a 'bottom-up' sc heme in which ACK trees grow from leaf receivers toward a root sender. This paper proposes an alternative 'top-down' configuration where an ACK tree b egins at the root sender and gradually expands by including non-tree nodes into the tree in a stepwise manner. The proposed scheme is simple and pract ical to implement along with multicast transport protocols. It is also empl oyed as a tree configuration in the Enhanced Communications Transport Proto col, which has been standardized in the ITU-T and ISO/lEC JTC1. From experi mental simulations, we see that the top-down scheme provides advantages ove r the existing bottom-up one in terms of the number of control messages req uired for tree configuration and the number of tree levels.