Video / Web conferencing

Video conferencing can be broken down into four basic types, described in the following sections.

Basic Web communication

At its most basic, Web-based video conferencing is communication between two computers in different locations, either on or off a corporate network.  Each computer has a low-cost webcam (e.g., those from Creative, Logitec, Sony or Apple’s iSight) for video, and a microphone/speaker for audio.  There is usually a "chat" capability, to exchange text messages. 

Such conferencing requires the use of a "middle-ware" application installed on each computer, such as AOL Messenger (AIM), Google Chat, iChat, MSN Messenger or Yahoo Messenger.  This middle-ware communicates back to a core/host system that manages the voice/video session. 

Web conferencing/collaboration

As with desktop conferencing, the end-points are computers that have low-cost webcams and audio.  However, this kind of conferencing relies on a more robust middle-ware platform to establish the connection and to share information. 

Multiple participants (more than two) can speak to and view each other, conduct chat sessions, upload and share documents, display their own computer's activity or take control of another user’s computer.

The middle-ware acts as a central "portal" into which users log in, and then activate their cameras, share files or other information.  Guests can be invited to the meeting by the system, and will get to the session through an email containing a special hyperlink developed for that session alone.   (In the physical world, meetings take place in a particular physical space; for a Web-based meeting, the "location" is a virtual space that the hyperlink specifies.)

NetMeeting, WebEx, and elluminate are examples of such a service.  For Medical Center affiliates, we offer this capability via the WebMeeting service based on Acrobat Connect (Macromedia Breeze).

"Conference room" conferencing

This is a further step up in quality -- and expense.  The communication is between two or more conference/meeting rooms, typically employing higher-resolution video conference cameras and higher-quality audio equipment (vendors in this product space LiveStream, Polycomm, and Sony).

In a two-way (also known as point-to-point) video conference of this kind, the cameras communicate with each other over a network (using TCP/IP) or by using older telephone ISDN technology.  (ISDN is still prevalent in Europe.)

In a video conference with three or more participating sites, a Multipoint Control Unit (MCU) or video "bridge" is required.  The MCU/bridge combines the video streams from the multiple cameras, and presents them in one view that is in turn presented on the television or computer screen of each participant.  It also provides an audio bridge that mixes the audio from all the end points.

In "voice switch" mode, an MCU determines who is the predominant speaker and automatically switches the video of that person to all the screens.  In "continuous presence" mode, it splits the screens and sends the video from each site to every screen.  In "chair mode," someone can manually control who is on screen at any given time.

The MCU typically has a scheduling utility, nowadays accessible from an Internet browser, to identify the physical locations to be connected and when to connect them.  From the video conference camera / TV setup, the user usually has the ability to pick from a drop down list of options (once populated with IP address, ISDN or DNS information) to further configure the meeting connection.

Purpose-built conferencing

This refers to the use of high-end video conference cameras and audio for particular applications.  Examples include:

• Telemedicine remote consultation services, allowing clinical diagnosis and treatment at a distance.  Implementations may be built on mobile carts or come with the ability to be hand-carried, and can include accessories like a "tele-stethoscope," "tele-otoscope," etc.
• Distance learning remote classrooms typically have a classroom environment established with a live video feed.  Some of these setups have an actual physical  classroom with professor in front, a live video feed coming for the session, and remote students listen/watch from off-site somewhere.
• Display of real-time research or clinical procedures, such as a camera connected to a microscope or placed above an operating room table.  On the other end, a classroom may be watching, a consultation being conducted, or it may be recorded for distribution later.

Quality and quantity issues

One quality variable should be obvious: the better the video and audio equipment, the better will be the images and sound that can be transceived.  Another variable relates to physical location: lighting and camera placement affect image qualify, as does the location of microphones in a room.   For high-end applications, a dedicated setting may be necessary.

The other variable is the speed and reliability of the connection between/among the connecting parties.  Unsurprisingly, you want the fastest connection possible for video conferencing solutions.  This way, you can maximize throughput and video will appear less choppy or pixilated.   (Audio consumes considerably less bandwidth than video.)

ISDN connections using the telephone network are relatively slow (rated at 128kbps unless your service "teams" multiple ISDN connections together for higher bandwidth).  As a rule of thumb, for high-quality video conferencing you need a minimum sustained connection of 384kbps.  This type of connection sustains a high-quality video and audio stream among the sites connecting.  And, for that, you need a high-speed Internet connection.

Standards for video conferencing

Like most aspects of information technology, video conferencing is associated with an oft-bewildering set of protocols and standards.  It's possible to use video conferencing happily and successfully without remembering any of them.  But, for the curious, these are some of the ones you will commonly hear referenced:

• H.263 and H.264 are ITU standards for compressing videos.
• H.320 is the ITU standard for dial-up networks, ISDN, T1 and Switched 56 services.  H.324 is used with regular phone lines and analog modems.
• H.323 is the ITU standard for voice and video over digital packet networks, which today means IP LANs and the public Internet.  SIP is the IETF standard for voice and video over IP.  MCUs may handle H.323 clients only or both H.323 and SIP clients. Most traditional IP video clients are H.323, but SIP is gaining ground.
• H.350 is the ITU standard for a video/conferencing directory.
• T.120 is the ITU standard for whiteboards, application sharing and application viewing, all of which can be used with or without videoconferencing.

More information

Video conferencing (Wikipedia)
Overview of the topic and links to additional information