Compositional Traffic in Networks on Chip Axel Jantsch, Royal Institute of Technology, Sweden Networks on Chip have emerged on the promise to provide a scalable SoC platform. In NoCs, unlike in buses, the addition of new computational resources automatically adds new communication resources. We call an NoC scalable if the demand on communication by computational resources is always matched by available communication resources for every size of the network. However, a quick analysis reveals that the communication demands may grow excessively for even moderately sized networks. Consequently, practical and efficient scalable NoC platforms must impose constraints on the communication load emitted by the computational resources. A related variant of the scalability concept implies that the addition of new applications on the platform is always matched by sufficient communication resources. Again, any cost-effective and scalable NoC platform must impose constraints on the traffic that new applications are allowed to add. This presentation will introduce the concept of traffic contract, which is an agreement between the network, the resource and the application about the amount and shape of the traffic between resource and network. We will discuss the properties of traffic contracts for analyzing communication properties in a network. In particular we will introduce compositional traffic contracts that allow for addition of new applications with predictable communication performance.