Robust Network Coding Using Diversity through Backup Flows

We introduce algorithms to design robust network codes in the presence of link failures for multicast in a directed acyclic network. Robustness is achieved through diversity provided by the network links and flows, while the maximum multicast rate due to max-flow min-cut bound is maintained. The proposed scheme is a receiver-based robust network coding, which exploits the diversity due to the possible gap of the specific receivers min-cut with respect to the network multicast capacity. An improved version of this scheme guarantees multicast capacity for a certain level of failures. In a multicast session, failure of a flow may not necessarily reduce the capacity of the network as other useful branches within the network could still facilitate back up routes (flows) from the source to the sinks. We introduce a scheme to employ backup flows in addition to the main flows to multicast data at maximum rate h, when possible. In a limiting case, the scheme guarantees the rate h, for all link failure patterns, which do not decrease the maximum rate below h. Here, the number of link failures may in general exceed the refined singleton bound.