In teleconsultation sessions, a critical dependency exists between the image contents and the type and sequential order of the image processing commands used by the various participants. Accordingly, for re-entrant/late users, a significant challenge exists in restoring the image contents of the teleconsultation session in such a way that all the participants maintain a consistent view of the medical images. In this paper, this problem is resolved using a novel recovery mechanism comprising two major components, namely an enhanced content-recording scheme designated as three-level indexing hierarchy (TIH) and a prioritized recovery policy. TIH maintains a record of all the commands which affect the appearance of each of medical images such that when a restoration process is required, these image-affect commands can be rapidly identified and transmitted to the user. As a result, a significant reduction can be gained in both the command identification/transmission time and the image restoration time compared to traditional recovery schemes, which restore the contents by re-executing all of the commands invoked during the course of the session. The prioritized recovery policy further reduces the time required for re-entrant/late users to catch up with the on-going session by utilizing the cross-linkage design within the TIH architecture to restore the foreground image (i.e. the image under current discussion) before the background images are restored (i.e. the remaining images in the session). To resolve the problem which arises when a background image is selected as the new foreground image before the restoration process is completed, the prioritized recovery policy maintains a set of resuming pointers for each re-entrant/late user to facilitate the process of suspending the current restoration process and switching to the restoration of the new foreground image. The evaluation results confirm that the TIH architecture and prioritized recovery policy yield a significant reduction in the recovery-latency delay compared to that required by traditional message-logging restoration systems.
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