Video conferencing is a two-way interactive communication, based on Internet or telephone technologies, which allows two or more locations to communicate simultaneously with each other using video, audio, still images and text.
Video conference is required when:
- for two or more parties live conversation is needed
- visual information (video, still images or text) is an important component of the conversation
- the parties of the conversation are at different physical locations (are not able physically to be at the same location)
- it is necessary to reduce or eliminate travel expenses and time.
There are different types of Video Conferencing Systems:
- Telepresence that is dedicated for large audience. It creates the feeling of being there for the people that are in a different location. Some sophisticated systems are based on 3D and holographic images with virtually invisible screens.
- Room-based systems are dedicated for the audience located in meeting room. It includes large screens and speakers.
- Desktop video is dedicated for individual use based on personal computer or IP phone.
- Video conferencing systems may be direct IP based (such as Polycom, LifeSize) or free software (Skype, etc.).
Based on the switching modes, videoconferences may be voice activated switch type, where only the one person talking may be seen on the screen or a continuous presence type, where all participants are seen on the screen simultaneously.
Based on the conferencing protocol, videoconferences may be circuit switched and packet switched. Circuit switched protocol videoconferencing (H.320) is based on information represented in a single bitstream, the communication bandwidth is not shared with other services but guaranteed, and like in a phone call the circuits are brought through the network on demand. H.320 protocol is used mostly in Integrated Service Digital Networks (ISDN).
Packet switched protocol videoconference (H.323) is based on information that is sent after it is converted to a sequence of individual packets, the communication bandwidth is not shared with other services but not guaranteed, and circuits are not available on demand. Packet switched protocol H.323 operates on IP based networks. This protocol is the most used.
Videoconferencing uses the following standards:
- Video compression and encoding: H.261, H.263, H.264.
- Audio compression and encoding: G.711, G.722.x, G.728.
- Signaling protocols in H.323 based videoconferencing: H.225 and H.245.