With the release of the April 14th, 2015 Lync 2013\SfB client patch (15.0.4711.1002) we introduced the idea of Multiplexed RTP\RTCP ports. This change was made to align with Web RTC standard and address NAT/FW traversal issues. What this means is that we will use a single UDP port for both RTP and RTCP when negotiating final candidates for Audio\Video modalities. This will affect all clients running the April 14th update regardless of which GUI interface is being used or against which server version is running on the backend. There is one caveat to the backend server version which I will discuss later.
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