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Chapter 5 - Monitoring Conferences
5-28
Dynamic Highest Common Mechanism (in Video Switching)
In Video Switching conferences, the Highest Common mechanism enables
the MCU to select the optimal video parameters for the conference according
to the highest video capabilities that are common to all the endpoints
participating in the conference. The Highest Common mechanism improves
the connectivity between endpoints, eliminates Secondary connections, and
facilitates Entry Queue Access and participant’s moves during conferences.
The Highest Common mechanism is applied to these video parameters:
• Video Protocol
• Video Format
• Video Frame Rate
• H.263 Annexes - N, F, T and I
• ProMotion
The selected common video is dynamically adjusted with each participant
connection to and disconnection from the conference. The Highest Common
mechanism is available with both H.320 and H.323 endpoints.
When the conference line rate is lower than 384 Kbps, the system first tries to
connect the participants using the H.264 video protocol. Only if the endpoint
does not support H.264, the system tries to connect the participants using
H.263 or H.261. For example, if all the connected endpoints support the
H.263 video protocol, the conference video protocol is set to H.263. When an
endpoint connects to the conference using H.261, the conference Video
Protocol changes to H.261, and all the endpoints will now connect to the
conference using H.261. When this endpoint leaves the conference, the Video
Protocol changes back to H.263, followed by the endpoints changing to video
protocol H.263. In this example, if the Video protocol was set to H.263, the
endpoint connecting using H.261 would have been connected as Secondary
(without the video channel) as it could not meet the conference settings.
When monitoring Video Switching conferences, the participant’s video
parameters can change during the conference, reflecting changes in the
conference video settings according to participant connections and
disconnections during the conference. Sometimes, lower video quality is
viewed during the conference as a result of changes in the video protocol (for
example changing from H.263 to H.261) or video resolution (for example,
from CIF to QCIF) and other video parameters.