High-bandwidth internet video telephony
We consider the problem of full-duplex video transmission over the Internet, under real-time delay constraints. In this work we present the design of a complete communications system, whose salient features are: (a) a soft real-time transport protocol, whose generated traffic characteristics are identical to those of bulk transfers using TCP/IP, thus ensuring complete fairness to other flows in the network; (b) a video coder resilient to moderate amounts of loss of data that are induced by the soft real-time constraint, and also by a continuous probing of the available channel capacity; (c) a unified control module, responsible for both congestion avoidance as well as coder configuration tasks; and (d) very low computational complexity. A key component of our system design is a predictive multiple description video coder working under feedback control. The whole system is implemented on a Linux PC, only in software, without making use of priviliged system calls (e.g., to raise the priority of a process). Using our prototype system, over certain high-speed segments of the public network we were able to deliver YUV signals of size 352x240 pixels, at about 15-25 frames/sec, and at average bit rates in the range of 0.5-1.5 Mbits/sec.