Handling Video-conferencing System

A video-conference (also known as video teleconference) is a set of telecommunication technologies which allows two or more locations to interact via two-way video and audio transmissions simultaneously. It is also called visual collaboration and is a type of group ware.

VTC system

There are basically two types of VTC system :

1. Dedicated system : This system has all required components packaged into a single piece of equipment, usually a console with a high quality remote controlled video camera. These cameras can be controlled at a distance to pan left and right, tilt up and down, and zoom. They are known PTZ cameras. The console contains all electrical interfaces, the control computer, and the software or hardware-based code. Omni directional microphones are connected to the console, as well as TV monitor with loudspeakers and/or a video projector. There are several types of dedicated VTC devices.

2. Desktop system : This is add- on (hardware board) to normal PCs, transforming them into VTC devices. A range of different cameras and microphone can be used with the board, which contains the necessary codec and transmission interfaces. Most of the desktop system works with H. 323 system. Video conferences carried out via dispersed PCs are known as e-meetings.

Technology employed

The core technology used in a videoteleconference (VTC) system is digital compression of audio and video streams in real time. The hardware and software that performs compression is called codec (coder/decoder). Compression rates of upto 1:500 can be achieved. The resulting digital stream of 1’s and O’s is subdivided into labeled packets, which are then transmitted through a digital network of some kind usually ISDN or IP.

The other components required for a VTC system include :

• Video input : Video camera or webcam

• Video output : Computer monitor, television or projector

• Audio input : Microphones

• Audio output : Usually loudspeakers associated with the display device or telephone

• Data transfer : Analog or digital telephone network, LAN or internet.

Multipoint Video conferencing

1. Multi Control Unit (MCU) : This is a bridge that interconnects calls from several sources. All parties call the MCU unit, or the MCU unit calls all the parties which are going to participate, in sequence. An MCU is characterized according to the number of simultaneous calls it can handle, its ability to conduct transposing of data rates and protocols, and features such as continuous presence, in which multiple parties can be seen on the screen at once.

2. ITU H. 323 Standard : There is no need of MCU if ITU H. 323 standard is used. This technique is known as “decentralized multipoint”, where each station in a multipoint call exchanges video and audio directly with the other stations with no central ‘manager’ or other bottleneck. The quality of audio is better but it requires high bandwidth.

Standards for VTC

The International Telecommunications Union (ITU) has three unbrellas of standards for VTC.

1. ITU H. 320 : It is the standard for public switched telephone networks (PSTN) or VTC over integrated services digital networks (ISDN), basic rate interface (BRI) or primary rate interface ( PRI). It is also used on dedicated networks such as TI and satellite-based networks.

2. ITU H. 323 : It is known as the standard for video over Internet Protocal (IP). This same standard also applies to voice over IP (VolP).

3. ITU H. 324 : It is the standard for transmission over Plain Old Telephone System (POTS) or audio telephony networks.

Application of VTC

The VTC has application in various fields for general and specific purposes such as:

1. Video telephony

2. Distance education

3. Telemedicine and telenursing

4. Telebusiness and telecommuting

5. e-meeting with farmers

6. On-line counseling to the farmers

7. Virtual field trips for farmers