We present the concept and implementation of a communication infrastructure for a distributed database system referring to the agent-based database query evaluation system AQuES. Within this model we use system components that build a federated multi agent system (MAS). We present those parts of the message transport layer that provide an “easy to handle”, scalable architecture based on the “plug & play” building block principle. Furthermore, we present a generic dialog manager that enables each agent to communicate in multiple concurrent threads of execution. Based on this concept, AQuES agents keep track of a complex evaluation environment in a dynamic, multi-query scenario.