Compared with the traditional client/server streaming model, peer-assisted video streaming has been shown to provide better scalability with lower infrastructure cost. In this paper, we describe how peer-assisted video streaming can be implemented through real-time service oriented architecture. Our architecture, dubbed PACTS, is composed of 5 distinct service components: directory service, content service, peer download service, peer upload service and rate composition service. PACTS is designed to meet the specific QoS requirements of different users, entered through a simple Web interface.??It also provides a distributed implementation of the content and peer directory services for effectively handling flash crowd situations, when a large number of users join during a very short period of time. We discuss the functionalities of the main PACTS services and specify the workflow of how these services work together to deliver real-time streaming services leveraging the benefits of peer to peer technology. By organizing elements of traditional video streaming and peer to peer computing into loosely-coupled composable middleware services and distributing them among participating entities, PACTS enables high-quality low-cost video streaming at a large scale and in real time.