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Appendix H - Deployment Into Microsoft Environments
Polycom®, Inc. 1002
Call Admission Control
Call Admission Control (CAC) can be enabled if the RealPresence Collaboration Server system is
configured with a Microsoft Edge Server. Call Admission Control (CAC) is enabled by manually adding the
flags to the system Configuration and setting their values as follows:
● To enable the Call Admission Control implementation in the Collaboration Server:
CAC_ENABLE=YES
● In addition, to ensure that endpoints such as HDX remain connected to the conference for its duration
when the Collaboration Server is configured with FQDN address and the Lync server is working with
load balancing and holds more than one address, the following two flags must be manually added
and set to:
MS_KEEP_ALIVE_ENABLE = YES
Note: Since the Keep Alive is only required when the Lync server is working with load balancing
and holds more than one address, the default value is NO.
SIP_TCP_PORT_ADDR_STRATEGY = 0
● When Call Admission Control is enabled in the local network, by default the local the ICE channel is
closed after applying CAC bandwidth management.
To change and preserve the ICE channel open throughout the call:
PRESERVE_ICE_CHANNEL_IN_CASE_OF_LOCAL_MODE=YES.
Conferencing Behavior
Continuous Presence Conferences
In Continuous Presence conference, Lync clients connect with any allocated bandwidth.
Video Switching Conferences
In Video Switching conferences, Lync clients must connect with the same line rate as the conference,
otherwise they will be connected as Secondary (Audio Only) participants.
Mitigation of the line rate requirement can be effected by modifying the system flag:
VSW_RATE_TOLERANCE_PERECENT.
This system flag determines the line rate tolerance.
Possible values are: 0 - 75.
Setting this flag to 0 (0% - default) determines no line rate tolerance and the participant must connect at the
conference line rate.
Setting this flag to a value between 1 and 75 determines the percentage of bandwidth that can be deducted
from the required bandwidth to allow participants to connect to the conference.
For example, if you enter 20 (for 20%) as the flag value, the participant will be able to connect to the
conference if the allocated line rate is up to 20% lower than the conference line rate (or between 80% and
100% of the required bandwidth). If the conference line rate is 1024Kbps, participant with a line rate between
819Kbps and 1024Kbps will be able to connect to the conference.
When a Tolerance is set, the Highest Common mechanism is enabled for the conference line rate. When a
participant with a lower line rate connects to the conference, the line rates of all other connected participants
are reduced accordingly. When the participant with the low line rate disconnects from the conference, the