Bridge/Multipoint Control Unit (MCU): An MCU can handle multiple simultaneous videoconferences, each with connections to many videoconferencing endpoints. Some videoconferencing endpoints are not capable of managing connections to more than 2 locations and an MCU facilitates these videoconferences.

The MCU assembles a series of interactive video streams into a single video feed. The incoming streams are generally sourced by videoconferencing stations or individual computers and each may have a different bandwidth capability and video quality. To overcome this challenge, the videoconferencing bridge uses special software to convert the video (and, in most cases, associated audio) streams into a single, easy-to-see video output that can be directed to other conference participants.

E.164: A video telephone number that is dedicated to a specific endpoint which contains only numeric characters and has a limit of 15 single digits.

Gatekeeper: A gatekeeper is a management tool for videoconferencing. Local endpoints (inside of campus firewalls) register with the gatekeeper to access services such as local and remote dial plans and the campus videoconferencing MCU bridge services. The gatekeeper can also provide interoperability between H.323 & SIP and IPV4 & IPV6.

Mobile endpoints that are registered with the gatekeeper will no longer be negatively impacted by frequently changing DHCP IP addresses. The mobile unit can benefit from a dedicated dial string (E.164) that can be used to allow far-end endpoints to dial to the local mobile endpoint.

H.320: An international standard protocol for videoconferencing that uses telecommunication lines for connectivity.

H.323: An international standard protocol for videoconferencing that uses the Internet for connectivity.

H.239: This protocol defines how additional media channels are used and managed by videoconferencing systems. It introduces the concept of data-showing where the PC desktop graphics are converted into a separate media stream and transmitted along with the main video stream. The new common denominator is the media stream, so it does not matter if the endpoint is PC or settop based. Endpoints that support H.239 will receive the dual streams and display the desktop graphics and far-end video in separate windows. Endpoints that don't support H.239 will display the graphics instead of the far-end video in one window, which may not be full screen.

Point-to-point Videoconferencing: Any two endpoints connecting directly with each other without using any bridging services. For example:

  • two offices in the same organization
  • you and an external business partner, college, or university
  • you and an off-campus student
  • virtual meetings on a one-to-one basis
  • virtual meetings between two small groups of people who are in different locations

Each videoconferencing endpoint sends the other its video and audio streams (ie, the input from a video camera and microphone connected to the endpoint). Each location receives the video and audio from the other location and views/listens to it using a monitor and speaker connected to their own endpoint.

To initiate a videoconference, a user at one end of the call must have the contact information for the videoconferencing endpoint they wish to connect to. This contact information can be:

  • A video telephone number: a set of numbers similar to a telephone number.
  • An IP address: a 12-digit number assigned to any device connected to the internet that uniquely identifies that device; ex: 123.456.789.123.
  • A host name: a "name" assigned to a device's IP address, usually to make it easier to remember, ex: 

The contact information used depends on the settings which are enabled at each site. Each type of contact information has its advantages and disadvantages:

  • Both sites will need to have access to a videoconferencing gatekeeper supported by your organization(s) in order to register for a video telephone number for the videoconferencing endpoint.
  • You will need to program your video telephone number in your endpoint's settings, but video telephone numbers are often easier to remember than IP addresses.
  • IP addresses are usually assigned to your videoconferencing endpoint automatically which saves you some trouble, but they can be difficult to remember and can change depending on a number of factors.
  • Host names are easy to remember and can be assigned permanently to a videoconferencing endpoint, but they are often difficult to enter into a remote control when dialing another site.

The point-to-point videoconference continues until one of the users "hangs up" the call.

Extra equipment may be necessary to present more than just video and audio to your audience. For example: to show small objects such as engineering parts, you may need a visualiser or document camera or to show medical specimens you may need a microscope with a digital adaptor. 

Multipoint Videoconferencing: Videoconferencing between more than two sites is usually referred to as "multipoint videoconferencing" and requires a specialized component referred to as a Multipoint Control Unit (MCU). The MCU can be:

  • An additional piece of software included within your local VCU.

This type of multipoint videoconferencing enables you to connect between four and six other videoconferencing endpoints to your endpoint, with your unit being designated as the "master" or the originator (and consuming one of the possible connections). All the participants can see and hear all the other participant’s video and audio and all the participants can send video and audio. The number of participants who can connect to your endpoint is dependent on the brand and model of endpoint that both you and the other locations you are connecting to have and whether your brand/model includes the MCU functionality by default or as an add-on.

  • An external device (MCU) somewhere on the Internet that you need to register with and connect your videoconferencing endpoint to. 

This type of multipoint videoconferencing can usually support larger numbers of participants.  It is typically more competent at dealing with different brands and models of videoconferencing endpoints and handling the use of more advanced features such as presentation mode or document sharing. However, providing this type of service requires a significant financial investment. Participating in a service like this usually requires the participants to contact external support people or organizations in order to register their endpoints.

The MCU connects to the Internet and registers with a videoconferencing gatekeeper, another piece of hardware that provides administrative control for participating endpoints. An external MCU, depending on its design capacity, can handle a certain number of simultaneous videoconferences, with each videoconference being logically separate from the others and with each having a specified number of users.

When users want to join a particular videoconferencing session, they dial the service number/password combination. The videoconferencing gatekeeper checks to see if that service has been registered by a MCU. The gatekeeper completes the call by connecting the client to the specified videoconference on the MCU.

Once the call has been connected, the site's audio/video stream is then sent over the Internet to the MCU. Similarly, other sites connect to the session and send their audio/video streams to the MCU. The MCU selects one of the audio/video streams on the videoconference and returns that audio/video stream to all of the sites (except the site whose stream was selected).

There are several methods for selecting an audio/video stream. Audio switching and chairman control are two alternatives. Typically, the method that is chosen is audio switching where the MCU selects the stream that currently has active audio (someone is talking or is talking the loudest).

As the user(s) at one site stop talking and the user(s) at another site start to talk, they capture the MCU. The process is repeated with the video from the newly selected site now being sent to all the other sites.

Streaming a Videoconference: If a user or site wants to participate in a videoconference but does not have videoconferencing units or internet connectivity with sufficient bandwidth, they can stream the videoconference using a browser on a computer. They will be able to see and hear the conference but not interact.

To stream the videoconference, users need to enter the URL of the server which then starts the encoded audio/video stream over the Internet to the computer. Plug-ins for the browser exist that are capable of decoding both RealVideo and Windows media streams. This allows the user to see and hear the participants in the streamed videoconference in near real-time.

Alternatively, a user can connect to the server at a later date and view the archived version of the videoconference. (ie. Matterhorn captured sessions).

Videoconferencing unit (VCU): A Videoconferencing unit has all the hardware components that are required to perform a videoconference packaged into a single piece of equipment.