Video-server designs for supporting very large numbers of concurrent users

Abstract

We present a design for a video server in which video content is stored in special video-delivery subsystems attached directly to network components such as switches or high-speed-network ports rather than the magnetic disk storage attached to conventional computer systems. Video is preformatted and stored in the form of network packets. This design approach overcomes the CPU- and I/O-bandwidth limitations of conventional computers in executing the file-system and network-protocol code for many concurrent video streams, resulting in higher performance at a lower cost. Two designs for the approach are discussed. The first extends the packet buffer of a shared-buffer switch with additional memory for storing the video packets. The second design uses a stream controller as the interface between an array of disks and a traditional switch or network port. We have built a prototype based on the second design. To avoid interference on the disks, data is interleaved across all disks connected to a stream controller in units of fixed playback time. This also reduces the jitter in the response time of the disks and, therefore, the size of the buffers needed to maintain interruption-free delivery. The cost benefits of both approaches are discussed.