Efficient and Lossless Multicast Support in Large Routers

Today, multicast-capable routers generally handle multicast traffic by appending each cell a local multicast output label (LMOL) containing a bitmap with as many bits as output ports, so as to identify the ports to which a copy of the cell has to be transferred. However, this approach is unfeasible for the very large IP routers having 128 output ports or more, because the LMOL length would rise above 16 bytes, thus the bandwidth wasted for transmitting LMOL will be intolerable for small cells. Recently, there come forth many approaches using various lossy compression algorithms to shorten the LMOL, hence to save bandwidth and improve efficiency. In this paper, we aim to offer both lossless replication and high efficiency for multicast traffic traversing in large routers, and present a scheme characterized by dual lookups and three-stage replications to achieve the goals. Experiment results show that the scheme can support multicast replication with no loss happening for large IP routers with as many as 128 x 128 output ports, in condition that the internal bus width being a normal value of 128, meanwhile, the scheme can also provide the most efficient transmission and replication.