We have built a “production” system and an advanced research prototype. The production system uses the commercial Java Message Service (SonicMQ) and has been used very successfully to build a synchronous collaboration environment applied to distance education. The publish/subscribe mechanism is powerful but this comes at some performance cost and so it is important that it satisfies the reasonably stringent constraints of synchronous collaboration. We are not advocating replacing all messaging with such a mechanism – this would be quite inappropriate for linking high performance devices such as nodes of a parallel machine linked today by messaging systems like MPI or PVM. Rather we have recommended using a.
