1，Point-to-point video conferencing
Video-enabled meetings happen in two distinct ways: either point-to-point or with multi-point. In point-to-point, the simplest scenario is where one person or group is connected to another. The physical components (i.e. microphone and camera) that enable the meeting to take place are often integrated in to desktop computing solutions like a laptop or tablet, or can be combined into dedicated, room-based hardware solutions.
Where desktop solutions tend to be used by individuals, room-based solutions utilize dedicated video conferencing technology where groups of people can be seen, heard and can naturally participate in the meeting.
2，Multi-point video conferencing
In multi-point video calls, three or more locations are connected together, where all participants can see and hear each other, as well as see any content being shared during the meeting.
In this scenario, digital information streams of voice, video and content are processed by a central, independent software program. Combining the individual participant’s video and voice traffic, the program re-sends a collective data stream back to meeting participants in the form of real-time audio and video imagery.
Individuals can participate in a meeting in an “audio only” mode, or combine audio with video images of the meeting on screen. Depending upon the technical capability of the video conferencing system being used, images seen by participants are either classified as “active speaker” or “continuous presence.”
In “active speaker” mode, the screen only provides an image of the person that is speaking at any point in time. In more advanced solutions with “continuous presence” mode, the bridge divides the image on the screen into a number of different areas. The person speaking at any point in time is presented in a large central area, and other meeting participants are shown displayed around the central image.
The “continuous presence” mode thus allows meeting participants to view and interact with all meeting participants in a ‘virtual meeting room.’
The software program which creates the “virtual meeting room” and the digital processing hardware on which it resides, is often called a video bridge, or “bridge”, for short. Another term for a bridge which is often used is a video conferencing “multi-point control unit” or “MCU.”
Whereas point-to-point video conferencing is relatively simple, the creation and management of multi-point video conferences can be complex. An MCU must be able to create, control and facilitate multiple simultaneous live video conferencing meetings. A further complexity is added when different locations may connect to the meeting over digital or analogue streams at different speeds, with different data transport and signalling protocols employed to facilitate the communication.
To link these users into a common, virtual meeting, the MCU must therefore be able to understand and translate between several different protocols (i.e. H.264 for communication over IP, and H.263 for ISDN). The MCU will also allow those joining the video bridge to do so at the highest speed and the best possible quality that their individual system can support. Although there are two separate processes taking place here, this is often jointly referred to as “transcoding.”
It is important to note that not all bridges provide such transcoding capability, and failure to do this can seriously impact the quality and experience of video calls. When transcoding is not provided and users dial into a bridge over a range of different connection speeds, it is possible that the bridge may only be able to support the video meeting by establishing the connections at the lowest common denominator. To illustrate the negative effect of this, consider a meeting that takes place with most users joining the bridge from the high-speed corporate network, but where one or two individuals dial into the meeting from home on low-bandwidth DSL or ISDN. In this case the experience of the many corporate users is downgraded to the lowest common denominator of the home-users, potentially making the video call ineffective. Where effective transcoding is supported by the MCU, those on the corporate network will continue to enjoy HD video quality, while remote users receive quality commensurate with their connection speeds.
In summary, when an MCU is designed well, integrating easily with multiple vendors and allowing users to call in at the data rate and resolution they want or need to—the result is an easy, seamless experience for all users, allowing people to focus on the meeting, not the technology.
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