Desktop Video-conferencing: A Basic Tool for
the 21st Century’s Communications Technology
Thao Mong Le
Computing Engineering, Inc.


Video-conferencing is simply a method for people in two or more locations to not only talk with one another, but to see each other and exchange information. Desktop video-conferencing (DVC) is an emerging technology of video-conferencing that uses a standard personal computer which has been enhanced with special video processing capabilities and a small camera. This technology is employed by a broad spectrum of users to facilitate cost effective communication with key individuals or groups regardless of their geographic location. This paper provides an overview of DVC and the feasibility of implementing DVC running on a 56 Kbps Wide Area Network (WAN) or T1 (1.544 Mbps) telephone systems, and Integrated Service Digital Network (ISDN), with a short discussion on these running on Local Area Networks (LANs).


Video-conferencing describes the use of compressed video technology for live, two-way, interactive communication in a variety of situations - person to person, informal discussions, formal group meeting, and large lectures. The primary use of video conferencing is to allow the timely exchange of information without traveling. Most meetings that are held face-to face can be held by video-conferencing. Video-conferencing is useful in situations of crisis management, or times when meetings are held on short notice.

Desktop video-conferencing (DVC) is an emerging technology of video-conferencing. This technology has been around since the early ‘90s when Cornell University researchers wrote CU-SeeMe that is a program that allowed Internet users with cameras and fast Internet connections to transmit live video. A DVC system uses a standard personal computer (PC) enhanced with special video processing capabilities and a small video camera with a speakerphone.

A DVC system allows two or more people using their PCs from different places to communicate through an audio and video connection. Connections between DVC systems can be made over Integrated Services Digital Network (ISDN) lines through regional and long distance telephone companies. A DVC system comes in three basic types: those that operate over phone lines, such as a 56 Kbps WAN/ T1 telephone service and ISDN, those that operate over a LAN such as Ethernet, and dedicated systems that use special video cables between each connected computer. This paper provides an overview of desktop video-conferencing and the feasibility of implementing DVC running on a 56 Kbps wide area network (WAN) or T1 telephone systems, and ISDN, with a short discussion on these running on local area networks (LANs).

Desktop Video-Conferencing Systems Overview

Desktop video-conferencing is gaining acceptance as a viable telecommunications technology. While a video-conferencing system uses the analog voice and video technology, a DVC system employs the digital audio and video technology offered real-time applications sharing that increases productivity of groups who need to work together but are split up geographically.
Designed to run on a personal computer (PC)-based platform, DVC systems are meeting the challenge of providing varied applications in the government and the commercial sectors. DVC systems take advantage of the windows multi-tasking environment, allowing users to maintain a live face-to-face video-conference while accessing many other applications on their desktops, such as spreadsheet and word processing.

In general, a DVC system has three basic parts to the screen: the video window, collaborative workspace and "Hollywood" squares. Conferees at sites are able to manipulate images, annotate text, etc., in real time. A conferee can take "snapshots" of information and send it as an image or send information in a file, while the video portion and audio connection stay active. Using a VCR, a desktop video-conference can be recorded for future use. DVC systems, either analog or digital, can be used by organizations as an enterprise-wide solution. An analog system can provide voice, real color images, and graphics at an analog bandwidth up to 4.5 MHz. This system uses digital PC White Board Windows applications that can operate on either a LAN or WAN through switches, DSU/CSU/ Modems or codec for hands-on interaction between a point-to-point or a multi-point conference. A digital DVC system offers more advanced features as well as provides more flexibility than an analog based-system. A digital system allows voice, vivid compressed color images, graphics, spreadsheets or any data file to be transmitted between remote locations within seconds.

According to telecommunications experts, the DVC technology is expected to be commonplace in 1998. (Network World, 10/95, Tackett). Programmable multimedia processors with video-conferencing capabilities now allow high performance achieved with low cost add-in boards for PC's (Waurzyniak, 1995). Additionally, many DVC systems are developed to provide an easier access for more users through the use of LANs.


Most current DVC systems use H.320 as an umbrella standard that embraces several other standards detailing how video and audio information is compressed and transmitted over wide-area digital services. In addition to H.320, there are a number of video and audio standards widely used for DVC systems. Some as discussed below.

Many other video and audio standards for DVC are in the work. Some of them include the transport of video and audio over the Internet (H.323), or company network and H.324 for direct modem-to-modem dial-up link, gateways for ISO-Ethernet, and high-speed Ethernet-to-ISDN and mobile communications. Intel also developed its Indeo, a video compression technique, to compete with H.320 and others DVC standards.

Hardware and Software

In addition to requring a powerful PC with a high resolution monitor, a  DVC system requires a pecific video-conferencing card, a color video camera, and a speakerphone. These will allow a DVC system to receive and send digitized audio, video, and text over LANs, WANs, or ISDN phone lines.  The DVC software allows a user to place and answer video phone calls, control video, audio, and text sent and received. Some versions of DVC software also support collaboration which provides for a shared software window, a shared clipboard, notes and a chalkboard.

Local Area Network and Internet Desktop Video-Conferencing

A Local Area network (LAs)  was designed to connect many PCs together. At the physical layer, a LAN usually consists of 10 Mbps Ethernet, or 4 to 16 Mbps Token Ring segments. Today, various DVC products support a variety of LAN protocols such as TCP/IP, Novel IPX/SPX, NetBIOS, and Aplletalk. To effectively use a LAN to transport video information, appropriate bandwidth is needed on that LAN. Every attempt must be made to avoid situations where the video applications have to contend with data applications for bandwidth. Video-conferencing is a bandwidth intensive application. Significant usage of desktop video-conferencing in a LAN is anticipated for both point-to-point and multipoint applications.

Since the current Ethernet network was not designed for streaming audio and video traffic, when a DVC system is implement on an existing Ethernet LAN, bandwidth may be a problem. The new ISDN-ISO 10BaseT Ethernet network technology can make DVC less stressful. This new technology allows the 10BaseT Ethernet and ISDN signals to be separated, so connecting video over the ISDN channels has no effect on the Ethernet. The fast Ethernet technology (100BaseT or 100VG-AnyLAN), which provides more bandwidth, can also make a DVC system to operate easier on a LAN. Finally, Asynchronous Transfer Mode (ATM) will eventually be the standard for transporting multimedia communication in both the local and wide areas.

Today, local distribution of the video-conferencing information over a LAN is technically feasible but is not recommended. Under heavy loading conditions such as the transport of video, the LAN would become overloaded, with the eventual result being a significant degradation in the quality of service with the possibility of total system failure.  Today, the Internet can connect various LANs together. Various DVC applications that operate over the Internet primarily use User Datagram Protocol (UDP) for video and audio data transmission over the Internet. Network Video (nv) designed by Xerox/PARC, and Cornell University CU-SeeMe are two video-conferencing tools that are widely used for DVC over the Internet.

Switched 56 Kbps Desktop Video-Conferencing

Switched 56 is a digital service that delivers the 56 Kbps bandwidth. The use of the SW56 service for a DCV system requires an installation of two 56 Kbps lines to each DVC user. In addition, a Channel Service Unit (CSU)/ Digital Service Unit (DSU) (with either an RS-449 or RS-530 data Terminal Equipment (DTE) interface and dialing support) for each line must be installed.

A SW56 based DVC system can be implemented using a SW56 capable video hub (e.g., the Teleos NetworkHub), which allows point-to-point DVC without using the public telephone facilities. A video hub system has combined functions of a dynamic circuit switch, a digital access cross-connect system, a drop and insert multiplexer, and an inverse multiplexer, thus eliminating the need to have a separate device to send/receive video-conferencing signals over a 56 Kbps WAN. The advantage of video hub system is to allow both dynamic circuit switched connection and static digital cross connection to operate simultaneously. A video hub system enables a DVC system to operate between two service sites, SW 56 T1 and ISDN-BRI/PRI. Figure 2 shows a typical implementation configuration of a Desktop Video-conferencing over a LAN-WAN-LAN network.


                    Figure 1. - A Typical Implementation Configuration of a DVC over a LAN-WAN-LAN Network

  ISDN-BRI Desktop Video-Conferencing

Most of the leading desktop vendors support the ISDN BRI DVC solution using the public ISDN service that incurs a fixed monthly charge and a recurring usage charge. The RBOCs offerred various ISDN services; most SDN services are available in a large metropolitan area, but iare not currently tarriffed everywhere. An ISDN-based DVC subnetwork can be implemented in each LAN using a video hub, which provides the ISDN BRI. Local video-conferencing is facilitated without access line
and usage charges from the LEC.  Figure 2 shows a DVC system configuration using ISDN service over a 56 Kbps/T1/FTS2000 network.

                     Figure 2. - Desktop video-conferencing Network Configuration Using ISDN Service

B-ISDN Desktop Video-Conferencing

Broadband Integrated Services Digital Network (B-ISDN) provides an integrated transport of voice video, data, and image information using scalable bandwidths from 51 Mbps to 622 Mbps. B-ISDN uses Asynchronous Transfer Mode (ATM) as the transport mechanism for its integrated multimedia payload. A B-ISDN DVC solution would imply the use of the public infrastructure. B-ISDN is still an immature technology that is not yet available. Implementing a B-ISDN based DVC solution today is technically feasible but is not economically viable. There is a strong interest in B-ISDN/ ATM from all sectors of the telecommunications community; however, the B-ISDN cost constraints and technology maturity makes the technology unattractive at this time.


DVC is quickly emerging as a viable technology for small or one-on-one communication from a distance. Most commercially available DVC systems allow users to send and receive video, audio, and computer files. A DVC system typically provides five to 30 frames per second (fps) of color motion video, audio, file transfer, whiteboarding, and possibly application sharing. As of today, a DVC system only talks with another DVC system that has the same standard (e.g., H.320).

The DVC technology offers solutions for a wide range of educational uses and business applications. Individuals or small groups can participate in distance courses or cooperate training using DVC. A DVC system is a good tool for staff meetings, project meetings, trouble shooting/crisis resolution meetings, financial planning meetings, product development meetings and customer support and training sessions. The DVC capability is crucial to businesses that have to analyze visual information rapidly. As a result, better decisions can be made with lower expenditure of resources. The DVC technology reduces costs that are easy to identify. Business exchanges can occur between executives or staff at different locations, thus reducing the expense and time delays inherent in travel.  DVC will never replace face-to-face contact. However it will add enough to a client meeting or a call home from a business trip to make it very promising.


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