Configuring Peer-to-Peer Video Options

Not only did Microsoft introduce enhanced video functionality in Lync Server 2013, but in Lync Server 2013 administrators are able to have greater control over Lync video functionality through in-band provisioning.

In Lync 2010 video bandwidth could be controlled through two key policies: the conferencing policy assigned to users, and the media configuration. In addition to these policies, Call Admission Control (CAC) could be used to control video bandwidth across sites.

In Lync 2013 the conferencing policy and CAC configurations remain, but the media configuration policy is no longer used by Lync 2013 servers and users.

Although it is called a conferencing policy, in Lync 2013 the conferencing policy still is the place where administrators will control video bandwidth for peer-to-peer and conference calls. The Lync Server 2013 conferencing policy includes new attributes that relate to peer-to-peer video and conferencing calls. These settings can be managed using the following:

• Get-CSConferencingPolicy

• Set-CSConferencingPolicy

• New-CSConferencingPolicy

The new attributes introduced with Lync 2013 are as listed here:

• VideoBitRateKb—This setting specifies the maximum video bit rate in Kbps for video that is sent by a user.

• TotalReceiveVideoBitRateKb—This setting specifies the maximum allowed bit rate in Kbps for all the video streams that the client receives. It specifies a combined total of all video streams, except for any panoramic video streams.

• MaxVideoConferencingResolution—This setting is for legacy clients only, but it does apply to Lync 2013 conferences. In scenarios with coexistence with Lync 2010 or older clients, administrators should consider configuring this setting as well.

The listed features are used in parallel with CAC, if both are deployed. The conferencing policy will specify how much bandwidth can be used for video irrespective of the path, while CAC will set a bandwidth limit specifically on the media path. For example:

• If the VideoBitRateKb is set to 500Kbps, and the CAC policy for the media path is set to 250Kbps, the limit will be set to 250Kbps.

• If the VideoBitRateKb is set to 250Kbps, and the CAC policy for the media path is set to 500Kbps, the limit will bet set to 250Kbps.

The preceding examples are pretty straightforward; the lowest limit will always take effect, which should be the desired behavior. It is important to carefully plan your conferencing policies and CAC configuration together.

A common question asked is how Lync enforces the bandwidth limits for media streams. Lync does not buffer packets because it can cause issues with the real-time media stream. However, Lync does dynamically adjust attributes of the codec to keep in line with the bandwidth rate that is enforced. This can also happen irrespective of any policies or CAC configuration. With video, there are much fewer tweaks that can happen when compared to audio streams; however, it is common for the frame rate and resolution of a video stream to dynamically adjust to respect policy enforcement, or real-time bandwidth congestion.

The “Lync Server 2013 Video Conferencing” section explains how these policies can impact conferencing scenarios.