Doç. Dr. Mr. Mustafa ALKAN / Telecommunication Authority
malkan@tk.gov.t

Hakan TEKEDERE / Gazi University

Videoconference Systems

As informatics technologies made us feel their power within this century, communication and exchange and transfer of the information gradually became a basic need. Systems that are more rapid, reliable and easy started to become prevalent. In the past, conference applications were being performed only through sound communication. Gradually, video transfer started to be performed.
Videoconference system is first realised in Bell Laboratories -USA between two places. This system is used for the transmission of a full-duplex analog television channel. In each conference room there were three cameras that see the speakers and there were voice switching system that transmit to the other side the output of the camera which comprises the speaker. Video of all participants are transmitted on the output of the fourth camera which has a wide angle of vision and which is on the side where nobody speaks.
"CONFRAVISION" of British Telecom and "Split-Screen" of Australia PTT followed the system of Bell Laboratories and NTT (Japan) and systems of other phone administrations followed the systems which are in the form of voice switching of Canada Bell's "Split Screen" systems that are at different locations. All of these systems are arranged by using the analog television transmission technology, standard television cameras and monitors. Videoconference systems that are based on digital transmission followed these studies. Canada Bell company benefited from the fiber lines of 45 Mbit/s that are between Montreal and Toronto. Commercial videoconference service of 2 Mbit/s started to be active in France in 1976. Existing Europe System is designed and standardised by 10 European countries as a network based on satellite and codec of 2 Mbit/s. Today, wireless visual communication technologies that are realised through GSM phones which directly perceive the satellite signals and transfer them -after converting into voice- on to the screen together with the data it carries, exist as the latest step of these systems.

Video Conference Unit
Video Conference Unit is an equipment which the user has direct contact. Utilisation easiness and things that can be done during a video conference session mostly depends on the capabilities of the video conference unit.
While the voice and video that are to be transmitted to the opposite side are provided by means of the camera and microphone that are connected to video conference unit, video of the other side can be watched on TV or monitor and the conversation can be heard through loudspeakers or earphones.
When selecting a video conference system, the most important point to take into consideration is the quality of the voice and video. Quality of the voice and video must be inspected on various connection rates. A qualified voice communication is a must item during a meeting. Therefore, quality of voice and its synchronisation with video must be controlled. Some products use receivers that look like earphone or telephone. However, in such a case, only the person who puts on the earphone can hear the conversation and talk. Videoconference equipment that is being used must support a loudspeaker connection. Besides, the microphone that is being used must also perceive the remote conversations. There must be a good echo-preventing system for a continuous and qualified voice.

Video Conference Architecture
Today, ISDN is the video conference communication standard which is prevalent worldwide. However, since IP will be the governing standard in the future and because ISDN infrastructure is not prevalent in Turkey, videoconference unit must support both IP and ISDN environments. In this way, protection of investment will be provided in the future.
For an active videoconference, a model possessing a mobile camera and remote control must be preferred. Since presentation during a videoconference is a prevalent application, the preferred equipment's possessing a PowerPoint presentation support will be an advantage.
Videoconference units are evaluated in two categories. They are desktop/card type and room/group type. Although they are cheap, desktop models have limited utilisation since they are not easy to use, cameras are stationary, requires a PC, have lack of harmony problems with PC hardware and their voice and video quality are usually below the required level. Desktop models may be assumed to be convenient mostly for data processing personnel or advanced PC users. Room (or group) type models have remote controls and mobile cameras. Because of their more qualified videos and utilisation easiness, they are preferred mostly by the managers and they are becoming widespread since their prices are decreasing gradually.
Most of room type systems submit TV output. This peculiarity provides addressing to many people through big televisions. PowerPoint presentation support and submittal of the presentation screen from a second television or projection equipment shall be preferred because it removes PC or big monitor necessity for the realisation of the presentation during the conference. It is possible to record the negotiations that are realised with the models that have video output.

Necessary Hardware for videoconference
Following hardware are required in the computer system which is necessary for participating in a video conference system;
Necessary Hardware for Video Conference
· A video/voice detecting card or a digital camera that can be connected to the parallel port of the computer in order to convert video into digital format by receiving the video from an analog camera and receiving the voice from a microphone,
· A voice card and a loudspeaker to repeat the received voice and a monitor to display the received video,
· A communication tool like a modem, ISDN card or a similar network interface for transmitting and receiving the information,
· A software that can realise document sharing and provide video/voice compression, multiplexing, assembling and management.
Hardware equipment that is being used in the desktop videoconference systems is also shown in the figure. Additional softwares, in other words codecs shall be used in order to provide the compression of video and voice information at the communication network inlet and the decompression of them at the network outlet.

Video Conference Types
Videoconference is realised in two ways; point to point conference and group conference (multipoint). In a conference between two people, computers are simply connected to each other through a videoconference program. In a group conference, many computer users may be included to the same conference.
In group videoconference system expensive equipment are used. This equipment is; big monitors, high quality cameras that are assembled automatically and follow the speaker throughout the conference, microphones without cable and other hardware. On group videoconference systems many computers may be included to the group. On desktop videoconference system there is camera, microphone, video/voice detecting card, PC and other hardware.
Today, videoconference is being carried on generally between two points. However, number of people participating in the conference session may be more than two. Among the products that are within this category are; videophones, desktop videoconference, roll-about systems that can be carried from one room to another and conference room systems.

Videophone
A two-way video transmission system on consumer level that uses existing phone lines as the transmission environment. Utilisation is limited between two people and has a small screen and video frame rate per second is between 2-10 frames. Videophone is first announced by AT&T in the year of 1964 and it was named as PicturePhone. First personal videophone system is put on the market by AT&T with the name VideoPhone 2500. Today, videophone is a telephone apparatus that has a small video camera and screen and is based on compression codecs. Dimension of its screen is 3.3 inches and the screen is coloured and its frame rate per second is between 2-10 frames. Operation quality of the system is limited with the broadband of the phone lines.

Desktop Videoconference
Desktop videoconference is a type of videoconference performed among two users or a small user group that are gathered around a single computer monitor. They establish communication with PC's that are equipped with similar systems over the PC's, special links or existing LAN's or WAN's. Video, voice and data transfer is provided between the participants of the session as if they are working side by side or having mutual conversations in the conference rooms. In these systems to keep video camera available is not a necessity and the continuity of the conference depends mostly on the voice transmission.
In from desktop to desktop conferences, real time drawings, plans, text or document images can be shared among the participants of the session. In such systems there are remote control indicators that will enable the remote people to show the details by indicating the specific points. Scanned documents, bitmap files received from databases or independent notes taken during the session can be transmitted to the opposite side.

Videoconference between multipoints
Three or more points can interact in a videoconference system that is being performed between multipoints. In such systems multimedia materials such as documents, drawings and video clips can be transmitted. These systems can be connected to equipment such as; facsimile machines, camcorders, digital cameras, scanners or portable units that are available on the area. An intelligent connection element that is on a central location and able to arrange the videoconference traffic between different units is necessary for performing multimedia conference sessions between more than two places and this element is called MCU (Multipoint Control Unit). Besides, the broadband of the network, that connects all the units to each other, shall be in such a capacity that will enable itself to carry the total multimedia traffic flow.

Multipoint Conference Unit
MCU fulfils the switching function by distributing real time voice and video signals to the participating parties of the conference. These units may be existing at any point on a videoconference network. MCU's receive the digital signs from codecs and directs them automatically towards the points that they have to go. MCU's are technological products with an extremely complicated structure and they include strong processors and complex softwares. This equipment functions as a bridge element between the products of various producers.

Multipoint Conference
As shown in the figure, MCU, that is being used in the multipoint videoconference system - which is different from a point to point videoconference-, manages the connection between the parties that are connected to videoconference system. There are two methods to provide the highest video quality and to decide by which site the video channel's control is being performed and they are;
· To select the speaking site or sites automatically and to realise the transmission priority,
· To assign one of them for manager mode and to select the site that has transmission priority.
At the same time, MCU broadcasts videoconference from one site to the other sites and provide the management and connections of the participant sites. Basic components of MCU are listed as; network interfaces, voice processing (coding-decoding) units, video switching, data processing, conference control, information invoicing and conference reservations.

Resources
1. Wu, C.H., Irwin, J. D., Multimedia Computer Communication Technologies. Prentice Hall, 1998
2. Kuo, F., Effelsberg, W., "Multimedia Communications Protocols and Applications", pp. 92, Prentice Hall
3. ITU-T Recommendation H. 320, Narrow-Band ISDN Visual Telephone Systems and Terminal Equipment, 1993.
4. ITU-T Recommendation 1.500, General Structure of the ISDN Interworking Recommendations, 1993.
5. Help, G., "Dictionary of Communications Technology", 1st Edition, ISBN 0-471-95542-6, John Wiley&Sons, Printed in Great Britain, 1995.
6. Wireless Multimedia Communications Networking Video, Voice and Data, Ellen Wesel, Addison-Wesley, ISBN 0201633949, December 1997.
7. ALKAN, M., TEKEDERE, H., Videoconference Systems, A New Dimension in Communication. Communication Broadcast Magazine, June-2000.