QoS tagging of the media is performed by the Lync client itself, so it must be provisioned in a way that it understands what ports to use for each type of traffic. By default, no tagging is done and all traffic uses the port range 5350–5389. The Lync client supports using different port ranges for the following types of traffic and recommends using a minimum of 20 ports per modality. This roughly translates to 20 concurrent calls per modality, which should be more than enough for any single endpoint.
First, to enable separate port ranges for each media type, run the following command:
Set-CsConferencingConfiguration -ClientMediaPortRangeEnabled $true
Next, define a unique port range for each type of traffic. As an example, ...