Hierarchical coding is a promising technique for handling real-time continuous media (i.e., video, audio, etc.), where timely presentation might be more important than totally lossless presentation. Hierarchical coding allows the receiver to have, and if desired present, a progressively better image as data is received and also allows the network to intelligently discard less important packets when congestion is encountered. We present the results of a simple hierarchically encoded image animation in various environments (hosts and networks). Presented here are results of the quality of the animation when loss was experienced, throughput rates achieved by the animation, near maximum user-to-user throughput rates of the environments tested, and maximum and average packet loss per frame experienced in the experiments. The highest visually-tolerable packet loss per frame was found to be about 2-3% for this animation and those environments. The highest animation rates and maximum throughput rates were measured between two DEC Alpha workstations connected via an FDDI ring. We were able to achieve animation rates of 4.4-5.2 Mbps with 0-1.3% loss, and maximum throughput rates of 33.2-42.1 Mbps with 0-3.4% loss. The maximum throughput rates are much higher because no image processing was done in those experiments, only reception of the image data and recording of statistics. However, in the animation experiment images are processed and displayed which reduces the throughput achieved.




Download Full History