Desktop Video Conferencing

The basic hardware components are:

• Camera, usually attached to the top of the monitor
• Microphone
• Speakers - even where speakers are built in to a workstation, external ones will provide better quality audio. Alternatively headphones may be useful, particularly in a shared office.
• Video board - to capture the signal from the camera and convert it to digital form
• Network card - usually an Ethernet card for connection to the LAN
• The usefulness of any particular system will depend on the kind of tasks it is expected to perform, e.g., are shared applications are required, very good video, very good audio?

When using LANs, full screen full motion video (25fps) will not normally be possible. The software will incorporate some kind of codec to compress the video. The level of compression can be up to 100:1, though the higher the level of compression, the lower the quality, and the quality will be much lower if there is a lot of movement. Even at high levels of compression, full screen video may not be possible. LANs were not designed to handle the constant bandwidth necessary for good video conferencing, but more `bursty´ data, which does not require real time transmission or synchronisation, and as the traffic on the LAN increases video conferencing may become unusable.

Multicast is one solution allowing many to many conferences over bursty networks. Multicast means that data is only sent once, but can be received by every participant, so only one channel is required regardless of the number of participants. The Multicast Backbone (MBONE) allows video conferencing to take place over the Internet. MBONE is known as a virtual network because physically it shares the same media as the Internet, using routers that can support multicast. Audio and video are compressed and they must still compete with other traffic on parts of the network, so the quality of MBONE video conferencing is limited.