Remote Stereo Viewer
Description and Past Work: The Remote Stereo Viewer (RSV 2.0) is a client/server application that provides immediate access to large sets of high-resolution stereo images. The image sets are organized as multi-dimensional grids. Each image set has at least one dimension, consisting of a series of images forming a 360° revolution of viewpoint around an anatomical subject. Consecutive images around this rotation axis are used to construct a stereo view of the object. Horizontal mouse motion moves the image in this dimension through the image set. Additional dimensions, mapped to vertical mouse motion, may show the structure at various levels of dissection or magnification. The application assumes that the learner will view only a "small" selection of the images and consequently does not warrant downloading the entire image set. RSV 2.0 uses the InformationChannels framework and includes the ability to form collaborative groups of learners. The content includes both hand and knee image sets, labeled for use in anatomical study.
Network Characteristics: Image sets are stored on the server as JPEG images and transported to the client on demand using a UDP layer protocol. The transport rate is configured to be equal to the JPEG decompression rate of the client, allowing the client to interleave receipt and decompression of data. Between Stanford and LaCrosse, transport produces bursts of between 30 and 40Mbps.
End-to-end Performance Support: We further developed this application for use with our testbed networks. RSV 3.0 incorporates the new collaboration and end-to-end performance support of the core infrastructure. Specifically, we modified the client to report actual image transport performance information to the WeatherHistory mechanism. The client also queries current weather conditions and uses this information to optimize its behavior accordingly.
All clients in a collaboration group currently have independent connections to the image server and submit separate image requests. Thus, the server repeatedly sends the same image to each client in a collaborating group. The new version incorporates a multicast address group to transport image data to collaborating clients, significantly improving the application's scalability.
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Scalable Transport in RSV: RSV is designed to support unpredictable navigation through large image sets. Typically, images are sent in high bandwidth bursts where the burst duration is a fraction of the total round-trip time. Since this means that the transport link would be idle for significant periods of time, the client pre-fetches images in the neighborhood of the last request to utilize the available capacity of the transport link as long as this does not negatively impact transport efficiency. The client can also adjust the image resolution requested to better balance use of the transport link. The performance data logged by RSV consists of its transport success experience (packet loss percent, percent of images transported with zero loss) at different send rates.