Fault tolerant video on demand services

This paper describes a highly available distributed video on demand (VoD) service which is inherently fault tolerant. The VoD service is provided by multiple servers that reside at different sites. New servers may be brought up "on the fly" to alleviate the load on other servers. When a server crashes it is replaced by another server in a transparent way; the clients are unaware of the change of service provider. In test runs of our VoD service prototype, such transitions are not noticeable to a human observer who uses the service. Our VoD service uses a sophisticated flow control mechanism and supports adjustment of the video quality to client capabilities. It does not assume any proprietary network technology: it uses commodity hardware and publicly available network technologies (e.g., TCP/IP, ATM). Our service may run on any machine connected to the Internet. The service exploits a group communication system as a building block for high availability. The utilization of group communication greatly simplifies the service design.