Video Conferencing









Typical Videoconference Setup

The typical videoconference setup consists of the codec with camera inputs, PC inputs (DVI / VGA), display outputs (DVI / VGA), mic inputs and audio outputs. Two projections or flat panels are used to display the persons of the far end and computer graphics that is transferred via the second videoconference channel (data channel).



Echo Cancelling

Because of loudspeakers and open microphones on both sides, plus audio transmission delay, audible echoes will occur if no further processing is included. The microphone feed from the near side is transmitted to the far side and amplified in the room via loudspeakers. The microphones in the far end room pick the signal up and transmit it back to the near side. Here it will be audible in the loudspeakers with the amplified far end signal. Because of the transmission delay audible delays will be between some milliseconds up to several hundred milliseconds.
A processing is needed that cancels the far end signal out of the backward transmitted signal to make sure that signal is not fed back to where it came from.

See: Echo Cancelling.

Echo cancellation makes it possible to communicate fully duplex in real time without audible echoes.



Videoconference Room Design

Location
As the perfect location a room should be chosen that is isolated from noise distractions such as lift shafts, air conditioning and all other audible machinery. Also make sure that outside traffic noise is not audible in the room. The nearby corridor should be carpeted to avoid loud steps of hard shoes (high heels?).
The room should have one or two doors that are outside of the camera angle to not have the image distracted by entering or leaving persons. The door(s) should have an adequate sound proofing and should shut silently!
If possible avoid any daylight in the room to make sure you have the same color temperature for the camera image all day long.

Lighting
The best lighting is indirect fluorescent lighting with an asymmetric design. The light should come in the direction of the camera 'look' from an angle between 45 and 60 vertical. This will avoid shadows in the eye sockets and under nose and chin. Horizontally the lighting should be very smooth and wide.



main lighting angle




wide horizontal dispersion for smooth lighting to avoid face shadows


  

asymmetrical light source

The optimal lighting level is between 450 and 600 Lux measured on the faces (measured horizontally in front of the face not vertically). The color temperature should be 3000K to 3500K. All lamps must have the same color temperature!
The lighting should be controllable in groups. For regular meetings in the room and for video conferencing different settings can be programmed.

Walls and Decor
Wall colors should be in lighter shades of blue or grey. These are the best choices for background colors and better than white. Especially the rear wall should never be white or very dark colored. A neutral grey tone is the best choice. Definitely any shiny surfaces and strong bold colors should be avoided in the area of possible camera angles. All finishes should be free from any patterns that may distract camera images.
Specific backdrop blinds could be considered. These can be changed if required.

Furniture
All furniture should have a matt surface. Any shiny metal parts should be avoided because it can cause reflections.

Room Acoustics
Walls and ceiling should be treated to reduce noise and acoustic reflections. The reverberation time should be very short (0.3 .. 0.5 sec). Ambient noise levels should as low as possible. Ideally an NC-30 noise rating should be achieved. The floor should be carpeted with a heavy underlay to provide additional acoustic damping.

Audio
The distance between microphone and loudspeaker should be at least five times the distance between microphone and talking person. Good quality loudspeakers should be used to ensure good speech intelligibility of the far end. for a one-person-conference a lavallier mic is always the best choice. Boundary mics should be positioned carefully to avoid accidental putting papers onto it. For a larger setup in a room with good acoustic conditions ceiling microphones can be a good choice.

Videoconference Table The table should fit to the number of persons that will participate normally on a video conference. For more that three persons a trapezoidal table form is suggested to get approximately the same camera distance for all persons. Also no person should be covered or blocked by another person in the camera image.



trapezoidal table



Camera Position
The camera position should be (if possible) in eye height in the middle between two displays. If only one display or one projection is used, the camera is mostly better positioned under the displays then on top. A camera height of approximately 1.2m fits best in most cases. If the camera is positioned beneath the display, in the transmitted camera image the persons look over the camera and it looks as if they 'look up'. If the camera is on top of the display, in the camera image they 'look down'. Both situations create a uncomfortable feeling for the persons at the far end because they don't look 'in the eyes'. Using two displays and putting the camera in the middle between them creates a better image because persons will look for and back between the two displays in the same height as the camera, giving the impression that they look 'in the eyes' of the far end people.


Tandberg
Lifesize
Sony
Polycom
Aethra
Radvision
Dialcom


Standards:

H.320 - Videoconferencing on ISDN, this standard has been in place for a decade and videoconferencing today is most commonly implemented on ISDN, providing high quality because its synchronous nature with very low delay and delay variation. ISDN is able to implement videoconferencing at transmission rates from 64Kbps up to 2Mbps. At 128Kbps, videoconferencing on ISDN is only of marginal quality and cannot really be considered suitable for most business uses. ISDN-based videoconferencing at 384Kbps can be considered the baseline of business quality videoconferencing and provides a high quality transmission of videoconferencing. The implementation of ISDN at speeds of 384Kbps and above is costly and a complex undertaking. Three 128Kbps Basic Rate ISDN (BRI) interfaces must be used for every videoconferencing device. Using a device called an IMUX, these three BRI lines must be bonded together to form a single communications channel.

H.321 - Videoconferencing over ATM, business quality

H.323 - Videoconferencing over TCP/IP Protocol, videoconferencing on frame based networks (Ethernet, Token Ring, FDDI, ATM) using TCP/IP protocol, allows for 2-way voice and video connection over the Internet (IP).
There are two basic types of H.323 videoconferencing connections: Point-to-point Videoconferences and Multipoint Videoconferences
when 3 or more systems conference together by calling a video bridge.

H.324 - Videoconferencing over POTS, Low Quality

H.310 - Videoconferencing MPEG-2 over ATM, Broadcast Quality, MPEG-based videoconferencing, different from H.320 and H.323. Two-way MPEG2 videoconferencing, requires up to 15Mbps of bandwidth, hardware costs are higher. Very good quality.

H.239 - Dual Stream Videoconferencing is the standard for the transmission of two streams at the same time, used for video and data (PC) transmission. The data transmission (usually in the XGA format) is used to carry additional PC presentations, Excel files etc. parallel to the video conferencing video stream.