  This paper introduces the \emph{RoboCast} communication abstraction. The
RoboCast allows a swarm of non oblivious, anonymous robots that are only
endowed with visibility sensors and do not share a common coordinate system, to
asynchronously exchange information. We propose a generic framework that covers
a large class of asynchronous communication algorithms and show how our
framework can be used to implement fundamental building blocks in robot
networks such as gathering or stigmergy. In more details, we propose a RoboCast
algorithm that allows robots to broadcast their local coordinate systems to
each others. Our algorithm is further refined with a local collision avoidance
scheme. Then, using the RoboCast primitive, we propose algorithms for
deterministic asynchronous gathering and binary information exchange.
