Video conferencing uses telecommunications of audio and video to bring people at different sites together for a meeting. This can be as simple as a conversation between two people in private offices (point-to-point) or involve several sites (multi-point) with more than one person in large rooms at different sites. Besides the audio and visual transmission of people, video conferencing can be used to share documents, computer-displayed information, and whiteboards. Improvements are being made in collaborative tools that allow people at different sites to electronically manipulate a common document or computer application.
IEEE standards guide the development of video conferencing. The H.320 standard describes how video conferencing operates over ISDN telephone circuits (The ISDN communications standard specifies how a single wire or optical fiber can carry voice, digital network services, and video. Typically, an ISDN circuit has more bandwidth than a regular analog telephone circuit.) H.323 describes how video conferencing operates over the Internet (TCP/IP or just IP). Multipoint Conferencing Units (MCUs) handle the traffic flow in multi-point video conferences and typically include gateway capabilities to bridge H.320 and H.323 sites together in a conference.
The quality of a video conference primarily depends on the characteristics of the circuit between the conferencing sites. In the H.323 world, a high-quality conference (excellent audio and video) needs about 768Kbs (KiloBits/Second) of bandwidth. On campus, this is usually possible since most data connections are at least 10Mbs (MegaBits/Second). It’s also possible when the other sites have Internet 2 capabilities (the next-generation Internet which is in use at virtually all R1 research universities and some business and government sites).
When a conversation includes a site off-campus, then bandwidth and type of connection between campus and the other site must be considered. If this path travels across the commodity Internet, then you are at the mercy of the activity on this public utility at the time of the conversation. Here are some general rules of thumb for bandwidth:
- 786 Kbs – On campus or another Internet 2 site (excellent quality)
- 384 Kbs – Maximum good connection across the commodity Internet (IP) or through an ISDN connection
- 256 Kbs – Audio OK; video barely full-motion (not smooth); use only if 384 Kbs is not possible
- 128 Kbs – Audio marginal; not full-motion video; use only if 256 Kbs is not possible
ISDN or IP? If you have a choice of having an ISDN versus an IP connection with the off-campus site, you have two issues to consider: quality and cost. In many cases, there will be additional charges (for you or the site you are connecting to) for ISDN. In general, there are no additional charges for IP (based on the current funding model for data connections on campus). You will get consistent quality with an ISDN connection, but over the commodity Internet you do not have guaranteed bandwidth (i.e., quality). Do a test video conference well before the actual session to validate your choice.