6. Conclusion

We have designed and implemented a middleware system infrastructure (termed NetMedia) to support the retrieval and transmission of multimedia data in distributed multimedia presentation environments. NetMedia gives the application developers a set of services that transparently provide connection management, media data transmission, QoS management and synchronization of multimedia streams. The main features of NetMedia include the following:

A well defined API (Application Programming Interface), which lets applications access remote media streams transparently like a local file access.
QoS management with the help of the DSD and PLUS protocols.
A multi-level buffering scheme to control the collaborations between the clients and servers to achieve flexible data-delivery in distributed environments.
Inter-stream synchronization and organization of streams using synchronization rules.
Interactive control (like fast forward/backward playback) with immediate response for all multimedia streams.

The middleware can be readily used to facilitate various applications. An interactive learning environment, NetMedia-VCR, has been implemented for student tutoring, medical and military training, human resource development, asynchronous distance learning and distributed publishing.