| Tree-based reliable multicast protocols provide scalability by distributing error-recovery tasks among several repair nodes. These repair nodes keep in their buffers all recently received packets and perform error recovery for their receiver nodes. This work addresses two open issues in tree-based protocols. The first is how to construct a logical tree in an efficient manner. We propose three efficient hybrid schemes for constructing a well-organized logical tree with reasonable message and time overhead.;The second open issue is when to discard packets from the buffers of repair nodes. Discarding packets that might still be needed is unacceptable, because it would force the receiver nodes to contact the sender node whenever one of them needs a retransmission of a discarded packet. Schemes addressing this issue can be broadly divided into ACK-based and NAK-based schemes. ACK-based schemes require each repair node to receive one acknowledgement from each of its receiver node for each packet that node has received. NAK-based schemes impose a much lower feedback load on the repair nodes but do not let repair nodes know when they can safely discard packets from their buffers. We present three new buffer management schemes combining the strengths of both approaches. In addition, our third scheme takes advantages of the bursty nature of packets losses. These schemes provide acceptable compromise between ACK-based and NAK-based scheme both in terms of the number of feedbacks from receiver nodes and error recovery delay. |
