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Recent advances in technology have made the cost of videoconferencing
low enough--in terms of both dollars and communications bandwidth--that
it is growing rapidly in usage and deployment. Two basic modes of
videoconferencing are currently in use within ER, ISDN-based conference-room
videoconferencing (see Figure 6-5) and packet-based desktop videoconferencing.
The Video Conferencing Service (VCS) provides a full range of ISDN-based
videoconferencing services to the ESnet user community. Users can
check for available time slots and book conferences by accessing
the Video Conferencing Service Scheduler (VCSS), an on-line automated
reservation system. The VCSS tracks available resources,
Figure 6-5. Conference-room videoconferencing
schedules conferences, generates reports, and sends electronic
mail notification. The Video Conferencing Service also provides
the bridging equipment, multiplexers, and ISDN circuits necessary
to host multiway videoconferences. In addition, a Help Desk has
been established to assist VCS users with operational issues.
Other video conferencing services provided by this group include
support of open standards and an interoperability gateway for
conferencing with outside organizations.
The ISDN-based architecture currently in use within the ER community
employs VTEL videoconferencing equipment in ordinary meeting rooms.
Communications requirements are met via point-to-point circuits,
either dedicated or dial-up, operating at speeds of 128 kbps and
up. In order for two sites to share a two-way videoconference,
a communications channel must be established between them for
the duration of the conference. Multiway videoconferences (i.e.,
with three or more participants) require the use of an MCU (Multiway
Conference Unit) that essentially acts as a meeting chairman,
deciding who is "given the floor," that is, who is allowed to
speak to and be seen by the other parties at any given time during
the conference.
Desktop videoconferencing uses the participant's workstation monitor
for display of the incoming video, while the outgoing video is picked
up by a small camera that is typically mounted on or near the monitor.
The video and audio data are "packetized" into IP packets and "multicast"
over the Internet/ESnet. Within the ER community, the most commonly
used desktop video facilities employ a combination of publicly available
software packages developed in part at LBL.
A multicast is basically a selective broadcast in which data
are sent from one source to specified multiple destinations in
a way that minimizes redundant traffic over the intervening links.
To achieve this end, a virtual network called the Mbone
(for Multicast backbone) has been constructed on top of
the existing IP network. ESnet implemented its own segment of
the Mbone during 1993, constructing multicast routers from workstations
and locating them at strategic locations around the ESnet perimeter.
The ESnet Mbone is currently an experimental service provided
to the community to make it possible to share multicast data.
Present uses of this technology allow audio, video, images, and
raw data to be sent simultaneously to many users worldwide. However,
as of this writing wide-area desktop videoconferencing still has
some significant performance problems. Frame rates as low as a
few seconds per frame and frequent audio breakups are still typical.
Another problem is that packet-based videoconferencing generates
an enormous amount of traffic on a steady basis. For ESnet, this
creates a very large traffic load on an already heavily loaded
network. Even with the sophisticated compression schemes being
used, a single multicast "meeting" may generate more than 100
kbps of traffic continuously for hours.
While desktop videoconferencing is still an experimental service,
its deployment is growing steadily, and it promises to become
a mature offering within the next several years. ESnet-wide desktop
videoconferences have been held, allowing participants to contribute
to meetings without ever leaving their offices. In addition, the
ESnet Mbone is connected to the larger Internet Mbone, giving
our users the capability to interact in real time with colleagues
around the globe.
Go to other ESnet services:
Network Operations Management
Network Infrastructure Services
Information Services
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