  A broadcast on a nontrivial connected graph G=(V,E) is a function f from V(G)
to {0,1,...,diam(G)} such that f(v) does not exceed the eccentricity of v. The
cost of f is the sum of the function values. A broadcast f is dominating if
each vertex of G is at distance at most f(v) from a vertex v with positive
f(v).
  We use properties of minimal dominating broadcasts to define the concept of
an irredundant broadcast on G. We determine conditions under which an
irredundant broadcast is maximal irredundant. Denoting the minimum costs of
dominating and maximal irredundant broadcasts by gamma_{b}(G) and ir_{b}(G)
respectively, the definitions imply that ir_{b}(G) is bounded above by
gamma_{b}(G) for all graphs. We show that gamma_{b} in turn is bounded above by
(5/4)ir_{b}(G) for all graphs G.
  We also briefly consider the upper broadcast number Gamma_{b}(G) and upper
irredundant broadcast number IR_{b}(G), and illustrate that the ratio IR_{b} to
Gamma_{b} is unbounded for general graphs.
