Application-specific multiprocessor system-on-chip is required for high-volume future embedded systems. However, obtaining a good application-specific architecture could be an overly complex problem if we consider all the possible customizations. In this paper, we present Colif, a design representation that clearly separates component behavior and communication infrastructure. In addition, it has a flexible communication model that spans multiple abstraction levels. These features are suitable for a design flow where customizing communications and component behaviors at different abstraction levels are the central issue. The paper introduces the main concepts of Colif and compares it to existing system modeling approaches.