  We consider synchronous dynamic networks which like radio networks may have
asymmetric communication links, and are affected by communication rather than
processor failures. In this paper we investigate the minimal message
survivability in a per round basis that allows for the minimal global
cooperation, i.e., allows to solve any task that is wait-free read-write
solvable. The paper completely characterizes this survivability requirement.
Message survivability is formalized by considering adversaries that have a
limited power to remove messages in a round. Removal of a message on a link in
one direction does not necessarily imply the removal of the message on that
link in the other direction. Surprisingly there exist a single strongest
adversary which solves any wait-free read/write task. Any different adversary
that solves any wait-free read/write task is weaker, and any stronger adversary
will not solve any wait-free read/write task. ABD \cite{ABD} who considered
processor failure, arrived at an adversary that is $n/2$ resilient,
consequently can solve tasks, such as $n/2$-set-consensus, which are not
read/write wait-free solvable. With message adversaries, we arrive at an
adversary which has exactly the read-write wait-free power. Furthermore, this
adversary allows for a considerably simpler (simplest that we know of) proof
that the protocol complex of any read/write wait-free task is a subdivided
simplex, finally making this proof accessible for students with no
algebraic-topology prerequisites, and alternatively dispensing with the
assumption that the Immediate Snapshot complex is a subdivided simplex.
