A Delayed Consistency Model for Distributed Interactive Systems with Real-time Continuous Media

Xiao Qin
Griffith University, Australia

The advanced multimedia and high-speed networks make distributed interactive systems more promising and practical. These systems are distributed systems, which allow many clients who are located in different locations to concurrently explore and interact with each other. This system can be built in both the local area network (LAN), and the wide area network (WAN), such as the Internet. Operations issued at one site are immediately executed at the local sites for a good response time, and are propagated to other sites. One of the challenging issues in this system is the consistency maintenance. Such issue in the discrete interactive media has been studied in many literatures. Unfortunately, the consistency maintenance scheme for discrete interactive media is not suitable for continuous media domain. This paper illustrates a consistency problem in continuous interactive media by a simple example. The absolute consistency model, a strong requirement, is suitable for LAN, but result in a bad responsiveness in WAN. To make the model more practical for WAN, we propose a new consistency model named delayed consistency model. In this model, if there is an operation for an object x is issued at site i, every site should be able to execute this operation at a specified time. With this approach, other sites are forced to update the state at a certain amount of time later than site i does. Thus, other sites will finally view the same state of x as that of site i. Our model is flexible, because it is unnecessary for all sites to have the identical delayed time. If the system is based on the real-time network, then another advantage of the model is providing a useful parameter for real-time network scheduling.

Journal of Software, Vol.13, No.6, June, 2002

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