Desktop Video Conference
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Joined: Mar 2010
22-04-2010, 10:38 AM
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. Ideally, participants have an experience similar to watching and listening to one another on TV, with the added ability to interact, or 'talk back'.
Until recently, most videoconferencing was done with room videoconferencing systems, which require very sophisticated and expensive equipment to provide high-quality sound and video. Desktop video-conferencing is less expensive and requires personal computer.
This Project can be used in our college for various meetings that include all the department heads in our college. It is also useful for principal to talk with various staff members and with the management and get the things done at a faster rate. It is also useful to deliver online project and implimentation guidance to the students etc.
The primary use of Desktop Video-conferencing is to allow the timely exchange of information without traveling. There is no need for various persons to meet at a common place to make their conference. Most meetings that are held face-to face can be held by video-conferencing. Desktop Video-Conferencing is useful in situations of crisis management, or times when meetings are held on short notice.
Advances in computer technology such as faster processors and better data compression algorithms enabled the integration of audio and video data into the computing environment. Today videoconferencing can be achieved by adding software and relatively inexpensive hardware to standard desktop computers. Such systems, also, have the ability to easily incorporate data from other desktop computer applications into the conference.
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.
Desktop video-conferencing (DVC) is an emerging technology of video-conferencing. This technology has been around since the early Ëœ90s when Cornell University researchers wrote CU-SeeMe which 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. Our Desktop Video-Conferencing Application uses LAN for connections between DVC systems.
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 operating systemâ„¢s 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. 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 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 and graphics 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.
HOW IT WORKS
The basic process of desktop videoconferencing involves getting an image into your computer, sending the image to another computer, and displaying it to another person. Desktop videoconferencing can be done between two people at two computers, or among several people at several locations.
Let's consider how the image gets into your computer. Your computer needs a video camera in order to "see" you. The video that the camera captures is actually a series of still pictures called frames. The number of frames displayed per second is called the frame rate. A higher frame rate makes the video look smoother and more life-like. Desktop videoconferencing systems usually offer frame rates between 10 and 30 fps (frames per second).
The next step in the process is getting the images from your computer to your recipient's computer. To do this, your computers must be connected, or networked. No matter which type of connection you're using, the important thing to remember is that it takes time to send information (like images) across a network. The amount of time depends on what type of network you're using and how much information you're sending.
Now consider the importance of sending your video to its recipient instantly. In order to send the images quickly, you have to manage the image file size. You can do this by
using a lower frame rate, which sends fewer images each second. This makes motions appear less smooth.
lowering the resolution of each frame
compressing the images before sending them. In compression, your computer takes information (the data for a still picture, for example), and mathematically manipulates it so less data is needed to represent the information. Then, your recipient's computer reverses the process and displays the original information (the still picture).
In desktop videoconferencing, images are always compressed by your computer before it sends them over the network, and decompressed by the recipient's computer.
Images aren't the only information being sent during videoconferencing: sound is also compressed and decompressed. This process uses up a lot of bandwidth. A way to increase the speed of the video's transmission would be to not transmit sound (and telephone the other party, for example, to communicate verbally).
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 are discussed below.
Video Standard: H.261, also known as the ITU Px64, provides the specification for compressing real-time video at rates varying from 56/64 Kbps to 1.92 Mbps. H.261 covers both P x 56/64 Kbps (P = 1,2, ... 6) and M x 384 Kbps (M= 1,2,...5). The compressed video comes in two video quality modes (display formats), Common Intermediate Format (CIF) and Quarter-CIF (QCIF). The CIF provides for a 288 lines by 352 pixel picture and the QCIF a 144 line by 176 pixel picture. Theoretically, a CIF and a QCIF can transmit video at 30 frames per second (fps) and 5 fps, respectively. But except for dedicated wire systems, as of today, no DVC system transfers video close to 30fps over ISDN. The use of an ITU P x 64 standard-based desktop video-conferencing provides (1) interoperable DVC system; (2) multiple procurement sources facilitating competitive pricing; (3) increase product life cycle; (4) economical long term investment.
Video Framing Standard: The ITU H.221 standard is a framing protocol used for multiplexing video, audio, and control signals. It has the capability of aggregating 56/64 Kbps bandwidths to form a wider bandwidth.
Voice Standard: The ITU P x 64 recommendations support several audio standards. G.711 describes audio transport at 64Kbps pulse code modulation (PCM) digital audio from 3.5 KHz analog, G.722 uses sub-band adaptive differential pulse code modulation (ADPCM) to provide a 48Kbps or a 56Kbps at 7KHz analog signal (almost CD quality), and G.728 provides for near-PCM quality audio at a data rate of 16 Kbps at 3KHZ for low bit rate video.
Point-to-Point Control: Point-to-point conference control is facilitated by the use of the ITU H.230 and H.242 standards. The ITU H.230 standard provides control and signaling capability. The ITU H.242 standard provides for the set up and disconnect; inband information exchange, fault and channel management.
Multi-Point Conference Control: The ITU P x 64 standards associated with multi-point conference control (MCC) are H.231, and H.243. The ITU H.231 standard describes the overall architecture of multi-point control unit (MCU) using digital channels up to 2 Mbps. The ITU H.243 standard provides the control procedures between a ITU H.231 compliant MCU and ITU H.320 codecs. Some of the MCU services include (a) meet-me conferences, where conferees get a number in advance that will connect them to the conference; (b) dial-out conferences, where the MCU calls each conferee to initiate the conference; © progressive conferences, where a conferee calls successive parties and adds them to the conference one at a time; (d) Reservation systems; (e) Remote Maintenance; (f) Attendant screening of conferees for added security.
T.120 Standard: DVC uses T.120 as an umbrella standard for data sharing. This standard, which was to have been finalized last summer, allows for the sharing of information such as whiteboard, file transfer and so on between systems that conform to this standard even if the systems are not alike.
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.
Desktop videoconferencing always involves a computer at each end of the communication. Faster computers will usually be able to compress and decompress images faster, but videoconferencing doesn't necessarily require the fastest computers on the market.
Video can't get into a computer without a video camera. Because your computer deals only in digital information, you can't use the type of video camera that you use to make videocassette recorder tapes. (VCR tapes, like audio tapes, are analog media. Compact discs and computer disks are examples of digital media.)
Not long ago, users had to open up their computers and install a special card for the video camera. Today there are three types of cameras that can connect to a computer without using a video card. These cameras use the computer's serial, parallel and Universal Serial Bus (USB) ports. While serial and parallel cameras can connect to almost any computer, USB cameras can only connect to machines that have the new USB port.
The advantage of USB cameras is that they're able to support better picture quality and more frames per second -- that's because a USB connection can move more data at a faster rate than older connections (like serial and parallel). Today's new computers are usually equipped with USBs. There are several digital video cameras on the market. Some options to look for are:
color, zoom, and wide angle settings
the ability to take still pictures
automatic adjustment for different types of light
the ability to select which type of compression to use
No matter which camera you're considering, make sure your computer meets the camera's requirements (they usually require at least 16 MB of RAM and 256 color VGA display).
Youâ„¢ll probably also want a microphone and speakers on each person's computer (otherwise you won't be able to hear each other!). You can use any microphone that is compatible with your system's sound card (which you'll also need in order to hear each other).
To desktop videoconference you need a network connection to send the images between computers. Basically there are four options:
Â¢ Plain Old Telephone Service (or POTS)
Â¢ Integrated Services Digital Network (or ISDN)
Â¢ Dedicated video lines
POTS: To use POTS all you need is a telephone hookup, which you probably already have, and a modem. This is relatively inexpensive, but it is also by far the slowest type of connection.
ISDN: ISDN is a special digital phone with a much higher bandwidth than POTS. Bandwidth is the amount of information that can be sent across a network in a second. When you use ISDN, the entire bandwidth is dedicated to you and only you, so the speed never changes.
Ethernet: Ethernet is the primary type of networking on the Internet, and has an even higher bandwidth than ISDN (but with some drawbacks). When you use Ethernet networking, the total bandwidth is split among all the people currently using it, which means the speed you send things at depends on how many people are currently using the network.
Dedicated Video Lines: The fourth networking option is to install dedicated video lines, which are special cables used exclusively for videoconferencing. This is only feasible when you want to communicate within an office or school, since you'd have to set up the cables the entire distance between the two computers (Ethernet and ISDN connections are set up by a phone company).
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