Time bounds on fault-tolerant broadcasting

Broadcasting is the process by which a message originated at one vertex is delivered to all other vertices of a network, subject to the restriction that a vertex may participate in only one message transfer during a given time unit. A k fault-tolerant broadcasting scheme is a calling scheme that gurantees the completion of the broadcast in the presence of up to k link failures. Let Tk(n) denote the minimum time required for k fault-tolerant broadcasting in an n-vertex network. Liestman [Networks15 (1985) 159–171] showed that for every n and k such that n − 2 ≥ k ≥ 1, Tk(n) ⩾ [log n]+k. This paper establishes a matching upper bound, showing that for such n and k, Tk(n) ϵ O (log n +k). In particular, we present various efficient broadcasting schemes achieving almost optimal multiplicative constants. Our best upper bound uses new partial results on a tree-packing problem that may be of independent interest.