Videoconferencing over packet-based networks

M.H. Willebeek-LeMair, Zon-Yin Shae
1997 IEEE Journal on Selected Areas in Communications  
The Internet explosion is driving the need for new collaboration tools which will enable two or more users to share data, audio, and video. The real-time packet-based solutions which are emerging differ considerably from the circuitswitch solutions which have existed for some time now. In this paper, we present one such packet-based approach, the Multimedia Multiparty Teleconferencing (MMT) system, which was fully implemented as a research prototype. Using MMT as an example, we address some of
more » ... he fundamental issues related to videoconferencing systems in a packet-based environment, and discuss the differences with the traditional circuit-switch approaches, namely, the ITU H.320 standard. In particular, MMT is a distributed solution, while H.320 is centralized. The use of multicast and a novel video-mixing technique to facilitate the distributed solution are presented. Furthermore, MMT audio and video streams are susceptible to congestion and packet loss in the shared media packet-based environment, while H.320 streams use dedicated connections. As such, synchronization, error resilience, and dynamic rate control schemes for the packet-based system are presented. Index Terms- Distributed MCU, packet video, rate control, videoconferencing, video mixing. I. INTRODUCTION T HE recent overwhelming interest in and awareness of the Internet are increasing the need for, and consequent development of, collaborative computing tools of which videoconferencing is an important component. Videoconferencing solutions and standards have existed for some time now in the circuit-switched N-ISDN environment. Many new solutions are emerging which are designed for packet-based intranet and Internet environments, and a series of standards are being developed. Two distinct classes of videoconferencing systems exist today. In one class are the circuit-switched (e.g., narrow-band ISDN or the switched 56 kbit/s phone line) types of solutions. In the other class are the packet-based network (e.g., Ethernet and Token Ring, or more generally, IP network) solutions, which endeavor to carry real-time traffic over existing computer communications networks. Solutions for the circuit-switched and packet-based networks differ considerably. These network technologies differ in terms of bandwidth usage and availability, connection versus connectionless communication paradigms, jitter, latency, packet-loss (error) characteristics, etc. As a consequence, the solutions for videoconferencing are adapted to exploit the capabilities/characteristics of each network. These differences include the encoder/decoder (CODEC) technology for video compression and decompression, the methods used to
doi:10.1109/49.611162 fatcat:ml7ypz2infhirnaolcr3ckozni