Development of a Video Network for Efficient Dissemination of the Graphical Images in a Collaborative Environment

Introduction The Problem Statement Today's desktop video is an emerging technology. Business, industrial, and educational systems can all benefit from presenting video images to many users simultaneously. Video transmission consumes a great deal of network resources. A simple calculation shows (Goldman, J., 1995) that uncompressed full-screen motion video requires more than 80-megabits/second bandwidth. The majority of local area networks (LAN), which have the transmission speed of 10-16 megabits/second, cannot carry such traffic. New developments (Fast Ethernet, 100VG-AnyLAN) are not yet widespread. Although they can improve the performance of video distribution, uncompressed video traffic is unacceptable even for these networks. The main directions in reducing bandwidth requirements are: * employing various video compression techniques. By using an appropriate compression technique, the transmission of a high resolution compressed video may require 6-24 megabits/second bandwidth; * reducing the amount of video data, which has to be transmitted. It can be done by reducing the number of pixels per line, lines per frame, and frames per second. Of course, this reduction may be done at the expense of video frame resolution and full motion video quality. As an example, we can mention the CCITT's ( International Telegraph and Telephone Consultive Committee (now ITU-T) H.261 video transmission standard. It defines two different video resolution formats: Common Interface Format with 352 pixels by 288 lines per frame and Quarter Common Interface Format with 176 pixels by 144 lines per frame. The delay-sensitive nature of video information introduces another problem of video transmission. Ethernet, Token Ring, and FDDI networks allow delays in transmission of video data. One of the ways of solving this problem is employing such services as frame relay and ATM which are not widely used yet. Any video transmission in a local area network must coexist with other network activities. A huge amount of data involved in a video transmission slows down all other local area network operations. That can be very frustrating for users who are not involved in the current video session. In a real-time system the situation may even become dangerous because of delays in emergency information. Unfortunately, none of the above mentioned strategies can solve all the problems of video distribution. All of them have their own benefits and drawbacks. In this paper we consider one possible way of solving the problem of video distribution. We examine a Hybrid Analog/ Digital Video Network (ADViNet) which uses two parallel communication media: analog - for transmitting video images, digital - for data transmission. We present the model and architecture of a video network and ADViNet protocol. We also analyze the benefits and weaknesses of the video networks. Background The typical physical architecture of a Hybrid Analog\ Digital Video Network (ADViNet) includes two communication media: digital and analog. The digital medium is used by a regular digital network according to its type and topology. The analog medium combines a VGA bus with several additional control lines. All the monitors in the LAN are connected to this bus by special switches. Each monitor can work in one of the two states: local--when the user can work independently with his/her workstation; and remote--when the monitor is connected to a remote source of video information. The analog bus is controlled centrally from the control panel located near the master station. We have implemented ADViNet in a classroom/laboratory at the College of Staten Island. On the physical level in our video network environment we use a Computer Video Web (ComWeb). ComWeb is a commercially available pure hardware system for video distribution ("Computer Video Web", 1996). The analog transmission medium has a centralized manual control on the physical level at the control panel connected to the main hub or control can be programmed from the central station. …