  In a secure message transmission (SMT) scenario a sender wants to send a
message in a private and reliable way to a receiver. Sender and receiver are
connected by $n$ vertex disjoint paths, referred to as wires, $t$ of which can
be controlled by an adaptive adversary with unlimited computational resources.
In Eurocrypt 2008, Garay and Ostrovsky considered an SMT scenario where sender
and receiver have access to a public discussion channel and showed that secure
and reliable communication is possible when $n \geq t+1$. In this paper we will
show that a secure protocol requires at least 3 rounds of communication and 2
rounds invocation of the public channel and hence give a complete answer to the
open question raised by Garay and Ostrovsky. We also describe a round optimal
protocol that has \emph{constant} transmission rate over the public channel.
