Abstract— In many IP media services, the media channels are point-to-point, dynamic, and set up with the participation of one or more application servers, even though the media packets themselves travel directly between media endpoints. The application servers must be programmed so that media behavior is globally correct, even though the servers may attempt to manipulate the same media channels concurrently and without knowledge of each other. Our proposed solution to this problem of compositional media control includes an architecture-independent descriptive model, a set of high-level programming primitives, a formal specification of their compositional semantics, a signaling protocol, an implementation, and partial verification of correctness. The paper includes performance analysis, comparison to related work, and principles for making other networked applications more compositional.