Multicasting in interconnected networks

The state of the art in reliable multicasting protocols renders itself inadequate for group multicasting in environments where both intra-group and inter-group messages bridge several LANs. A particularly difficult situation arises if some LANs are managed by autonomous authorities. If autonomy is upheld, as a defacto condition, then LANs under different authorities can adopt different ordering criteria for group multicasting. The accommodation of heterogeneous ordering criteria is a problem that has been largely ignored. The authors propose the multi-LAN multi-order (MLMO) protocol, which supports a reliable ordered delivery service for both local and global messages. The MLMO protocol assumes an environment in which multicasting groups can have members belonging to different LANs, and each group can adopt either total or causal order for message delivery to its members. Characteristic to the protocol is a communication structure that can be aligned with the actual routing topology; thus, the number of necessary protocol messages is maintained. Furthermore, groups that adopt causal order are not forced to experience message latency solely because of coexisting groups that adopt total order.