Distributing digital TV over a hybrid packet- and circuit-switched network

TV distribution is changing rapidly as traditional analog systems are replaced by their digitized counterparts, which are more interactive and use bandwidth more efficiently. Existing digital distribution systems generally rely on installed communal cabling to deliver TV signals to household set-top boxes. Although this approach has the advantage of requiring a low initial capital investment, it cannot guarantee futureproof converged services such as high-definition video, voice, and high-bandwidth Internet access. By adopting a delivery platform such as an Internet protocol (IP) multimedia subsystem, various voice and video services can be run on top of an IP bearer network. The key challenge is that IP makes the stringent quality of service (QoS) and availability requirements of multimedia services difficult to meet. Building an all-service delivery platform on which more value-added options can be carried is becoming essential for carriers and vendors alike. The 3TNet project, supported by China’s high-tech 863 Program, is a pioneering research initiative to achieve this goal.1, 2 Instead of using an all-IP or all-optical architecture, 3TNet employs a hybrid solution, with circuit switching in the core network and packet switching for distribution and access. On the one hand, this greatly simplifies QoS provisioning and traffic engineering in the core, enabling it to take advantage of mature optical transport technologies. On the other hand, it also preserves the ease of use, ubiquity, and scalability of IP technology. In September 2006, five years after launching this project, a largescale field trial was carried out on the resulting 3TNet testbed. As many as 15,000 users across eastern China witnessed the success of this effort.3 Figure 1. Headend (HE) devices encode digital TV signals into separate multicast streams and push them to the optical network. There, IP multicast streams are aggregated and delivered to residential offices in point-to-multipoint connections. Finally, the access module sends the appropriate channels to household set-top boxes. FE: Front end. LAN: Local area network. LSP: Label-switched path.