2.2 Multi-point video conferencing

Six-way connection between Green Bank, Charlottesville, Santiago, Socorro, Tucson and AUI hosted by the VSX video hub in CV-ER230 using the NRAO frame-relay and the Internet via U.Va.

Any meeting between three or more sites requires use of a multi-conferencing unit or MCU, otherwise known as a video hub. The video hub receives all of the video and audio signals, then decides which video signal(s) to send to each site, depending on who is currently speaking.

The NRAO has several video hubs in which multi-site meetings can be hosted:

1. a six-way `VSX' hub built into the system in the main second-floor conference room at Edgemont Road in Charlottesville (CV-ER230),
2. a four-way `FX' hub built into the system in the main third-floor video conference room at Edgemont Road in Charlottesville (CV-ER311),
3. a four-way 'FX' hub built into the system in the third-floor conference room (SO-conf) at the AOC in Socorro, and
4. a four-way `FX' hub built into the system in the Charlottesville Edgemont Road Auditorium (CV-Aud.)

Video conferencing between Tucson, Socorro and the VLA Site hosted by the FX video hub in the SO-conf system. Note the use of the frame-relay path via Charlottesville to connect Tucson and Socorro.

The VSX hub in Charlottesville conference room ER-230 can host up to a six-way video meeting, i.e., between that conference room and up to five other video systems at the NRAO or elsewhere. The FX hubs in Charlottesville's room ER-311 or Auditorium, or in the third-floor conference room in Socorro can provide three- or four-way conferencing between these systems and others at the NRAO or elsewhere.

The multi-conferencing capabilities of these hubs are activated simply by placing more than one video call simultaneously from or to them. Multi-site calls can be initiated either by these hubs calling out, or by far sites calling in.) The FX hubs can support three-way meetings at bandwidths up to 512 kbps, and four-way meetings at bandwidths up to 384 kbps. The hubs cannot be used independently of the video systems in their rooms, i.e., to use the hubs you must also reserve the rooms.

Note that the four-way hub in the Charlottesville Auditorium is used mainly for NRAO-wide meetings, colloquia and workshops with a large audience in the Charlottesville Auditorium, and which require the use of auxiliary microphones and cameras. It may however be used for small meetings by rearranging seating and microphones in the Auditorium.

Five- and six-way meetings are also possible using multiple FX hubs, if one of the FX hubs calls the other as part of a multi-site call, then the second FX hub calls out to further sites.

During a multi-site conference, all audio channels are continuous and the video hubs use voice-activated video switching to decide which video signal(s) to send to each site. The video hubs are normally configured in a video mode which lets all sites see each other in a ``Hollywood Squares" format during multi-way discussion, but which switches to full-screen mode after 15 seconds if only one site is speaking. It is also possible to configure these hubs to send only the full-screen video from the site that is sending the strongest audio, or to stay in all-site discussion mode no matter who is speaking. It is always good etiquette for sites to mute their microphones while listening to a presentation during a multi-point conference, to ensure that other sites will receive uninterrupted full-screen video from the presenting site, and to prevent side-conversations at a listening site from distracting other meeting participants.

The inter-site time delay through any video hub is more noticeable than in point-to-point calls, so participants in multi-site meetings need to be aware that it takes a little longer to get an answer to a question, or to break into a discussion, than it is during a telephone meeting or a point-to-point video meeting. Also, when sites are connected through a video hub, only local (i.e. near) camera control is available through the Polycom hand=held remote controls. Each site must then be responsible for steering its own camera unless an arrangement has been made for camera control through the remote camera API (application programming interface), see Section 5.4..

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