Sharing Content During Conferences
Polycom®, Inc. 104
Content Transmission Methods
There are two methods used for content transmission:
●Content Video Switching
●Multiple Content Resolution

Content Video Switching

When using this method, content sent by endpoints is transmitted as-is to all content-capable participants.
The content rate is determined using one of the following methods:
●Highest Common
●Fixed Rate

Highest Common

The Highest Common method is applied in a few levels:
●Within the same protocol - The highest common content rate
●Between protocols - H.263 and H.264
In this method, the content rate is negotiated to highest common capabilities supported by the endpoints
connected to the conference. Therefore, if the conference includes participants supporting both lower and
higher content capabilities, the content is sent to all endpoints using the lowest endpoint capabilities.
Note, that when content is currently shared using H.263, the MCU determines the content rate, and the
endpoint sharing the content determines the resolution and frame rate. However, when content is shared
using H.264, the MCU determines content rate, resolution and frame rate (depending on endpoints
capabilities and conference settings).
When a new endpoint with lower content capabilities joins while content is shared, content sharing
parameters are downgraded to this endpoint capabilities:
●If downgrade affects the protocol (from H.264 to H.263), content sharing is terminated, protocol
automatically downgrades to H.263, or in H.264, and content sharing should be manually resumed.
●If downgrade affects only the content rate, resolution or frame rate (in H.264), the relevant content
parameters automatically downgrade during content sharing.
Once this endpoint leaves the conference during content sharing, no change occurs in the protocol or
content rate. In H.264 content, resolution or frame rate may automatically upgrade.
Content Setting Highest Common Calculation
For Graphics, Hi-res Graphics and Live Video (see Content Settings), the highest common content is
calculated for the conference each time an endpoint connects. Highest Common content bit rate is
calculated using line rate (the only factor for H.263), resolution, and frame rate (additional factors for H.264).
Therefore, if an endpoint connects to an ongoing conference at lower values of these parameters, content
parameters are re-calculated and decreased accordingly.
This method is applied for single MCU conferences.