Tele-immersive systems can improve productivity and aid communication by allowing distributed parties to exchange information via a shared immersive experience. The TEEVE research project at the University of Illinois at Urbana-Champaign and the University of California at Berkeley seeks to foster the development and use of tele-immersive environments by a holistic integration of existing components that capture, transmit, and render three-dimensional (3D) scenes in real time to convey a sense of immersive space. However, the transmission of 3D video poses significant challenges. First, it is bandwidth-intensive, as it requires the transmission of multiple large-volume 3D video streams. Second, existing schemes for 2D color video compression such as MPEG, JPEG, and H.263 cannot be applied directly because the 3D video data contains depth as well as color information. Our goal is to explore from a different angle of the 3D compression space with factors including complexity, compression ratio, quality, and real-time performance. To investigate these trade-offs, we present and evaluate two simple 3D compression schemes. For the first scheme, we use color reduction to compress the color information, which we then compress along with the depth information using zlib. For the second scheme, we use motion JPEG to compress the color information and run-length encoding followed by Huffman coding to compress the depth information. We apply both schemes to 3D videos captured from a real tele-immersive environment. Our experimental results show that: (1) the compressed data preserves enough information to communicate the 3D images effectively (min. PSNR > 40) and (2) even without inter-frame motion estimation, very high compression ratios (avg. > 15) are achievable at speeds sufficient to allow real-time communication (avg. ≈ 13 ms per 3D video frame).
In this paper we describe state-of-the-art peer-to-peer systems and analyze them according to multiple characteristics highlighting (1) scalability, (2) security and (3) fault tolerance. Peer-to-Peer systems are inherently scalable since they create fully decentralized environments across the Internet while simultaneously reducing complexity because each server handles a local set of clients. Peer-to-peer system security has depended primarily on user trust - the fact that any peer can contact any other peer in the system introduces issues of insider attacks from malicious users or external attacks through the Internet. Lastly, while peer-to-peer systems are evolving in response to peer unreliability, fault tolerance/survivability for general-purpose military group communications may require additional middleware.
Comparing these characteristics across different peer-to-peer systems is a step towards understanding which system may be appropriate for military group communications and where further research is needed. A secondary result of our comparison is an attempt to move towards common terminology and models between peer-to-peer, application-layer multicast, IP layer multicast, and distributed systems approaches for group communications.