The scenarios examined thus far have included agents that differ in any number of ways, including their sensory data, their goals, their actions, and their domain knowledge. Such heterogeneous multiagent systems can be very complex and powerful. However the full power of MAS can be realized when adding the ability for agents to communicate with one another. In fact, adding communication introduces the possibility of having a multiagent system turn into a system that is essentially equivalent to a single-agent system. By sending their sensor inputs to and receiving their commands from one agent, all the other agents can surrender control to that single agent. In this case, control is no longer distributed. Thus communicating heterogeneous agents can span the full range of complexity in agent systems.
Admittedly, communication could be viewed as simply part of an agent's interaction with the environment. However just as agents are considered special parts of the environment for the purposes of this survey, so is communication among agents considered extra-environmental. With the aid of communication, agents can coordinate much more effectively than they have been able to up to this point. In this scenario we include homogeneous as well as heterogeneous communicating agents.