Appendix - Media Traffic Shaping
Polycom, Inc. 352
System Flags
Traffic shaping usage is controlled by Collaboration Server configuration system flags (for the entire bridge):
● ENABLE_RTP_TRAFFIC_SHAPING - Enables traffic shaping. When set to YES, traffic shaping is
applied to all ports, resulting in some port capacity reduction (see Capacity Reduction). When set to
NO, traffic shaping is disabled.
● VIDEO_BIT_RATE_REDUCTION_PERCENT - Indicates the percentage of actual reduction in bit
rate sent from the MCU to the endpoint (negotiated bit rate is not reduced). This flag is applicable only
when traffic shaping is enabled (ENABLE_RTP_TRAFFIC_SHAPING set to YES).
Range: 0-60; Default value: 15
● TRAFFIC_SHAPING_MTU_FACTOR - Used for the MTU (Maximum transmitting Unit - the size of
transmitted packets) dynamic calculation:
New MTU = video bit rate / TRAFFIC_SHAPING_MTU_FACTOR
where the new MTU value is guaranteed to be a minimum of 410, and a maximum of 1460
(MAX_MTU). The purpose of this calculation is to match video rate in outgoing video to call rate, yet
force lower encoder bit rates to avoid overflow.
This flag is applicable only when traffic shaping is enabled.
Range: 0-5000, where 0 signifies no change in MTU; Default value: 800
To modify any of these flags, manually add them into the MCMS user parameters section of the system
configuration flags, and then modify their value (see Manually Adding a System Flag ).
Capacity Reduction During Traffic Shaping
The table below describes the maximum capacity left after reduction due to traffic shaping in Collaboration
Servers 2000/4000. There is no capacity reduction in Collaboration Servers 1800 and Virtual Edition.
System Limitation
Currently, Traffic shaping is limited to conferences using a minimum of 384 bit rate. Under this bit rate, the
user might experience bursts of data.
Capacity Reduction
Resolution Non-mixed Mode Mixed Mode
CIF 150 * 100 *
SD 150 * 100 *
HD720p 100 66
HD1080p 50 40
Audio Only 300 150
* Assuming conference bit rate ≤ 1024 Kbps
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