Lync Server has been designed to work without any Quality of Service (QoS) framework. It can be deployed with QoS implemented by using Differentiated Services (DiffServ). In Lync Server, DSCP marking can be enabled by using Windows policy-based QoS to specify port ranges for each communication type. By default, policy-based QoS and DSCP marking are disabled.The marked packets can then be recognized by network entities (end systems and routers if enabled to do so) to manage the media traffic according to the QoS priorities. The QoS marking is applied to all media ports and regardless of whether the audio/video/Application Sharing / File Transfer traffic is delivered over Real-Time Protocol (RTP; see IETF RFC 3350) or Secure Real-Time Protocol (SRTP; see IETF RFC 3711). To support the QoS environment, endpoints are configured to mark the IP traffic, thereby conveying the priority of the real-time audio and video IP traffic according to well-established classes of services that are designed to protect the real-time communication traffic from other asynchronous traffic in the IP network, including instant messaging (IM), application sharing data, and file downloads. These markings can be changed to map to different classes of services as an enterprise wants.
Also note that for clients that run on operating systems other than Windows 7 and Windows Vista, policy-based QoS is not supported.
