We have described adaptation-aware editing and progressive update propagation, two novel mechanisms for supporting multimedia authoring and collaborative work on bandwidth-limited devices. Both mechanisms decompose documents into their components structures (e.g., pages, images, paragraphs, sounds) and keep track of consistency and fidelity at a component granularity. Adaptation-aware editing lowers download latencies by enabling users to edit adapted documents. Progressive update propagation shortens the propagation time of components created or modified at the bandwidth-limited device by transmitting subsets of the modified components or transcoded versions of the modifications.
We demonstrate that support for adaptation-aware editing and progressive update propagation can be added to optimistic and pessimistic replication protocols in an orthogonal fashion. Specifically, new states are added to the state machines that describe the replication protocols, but the existing states and transitions remain unaffected.
We have described the implementation of our CoFi prototype, which supports adaptation-aware editing and progressive update propagation for optimistic client-server replication. We have presented performance results for experiments with multimedia authoring and collaboration with two real world applications. For these applications, the ability to edit partially loaded documents and progressively propagate fidelity refinements of modifications substantially reduce upload and download latencies.
While the experiments in this paper focus on document-centric applications, the same principles can be extended to applications with real-time requirements, such as video or audio. Adaptation-aware editing could be used to support video editing, while progressive update propagation would be useful in situations where there is a benefit in retransmitting a higher-fidelity version of a video or audio stream, such as when a user listens to a recording multiple times.