Quality of Service (QoS) Overview


Topic Last Modified: 2012-10-17

The quality of the service associated with synchronous traffic like audio or video can be affected by delay, jitter, and packet loss in the IP network. Although Microsoft Lync Server 2010 has been designed to work without any Quality of Service (QoS) framework, it can be deployed in IP networks with QoS implemented by using Differentiated Services (DiffServ). 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.

A network enabled for Differentiated Services (DiffServ) provides class-level prioritization based on Differentiated Services Code Point (DSCP) marking of the IP packets. Each DSCP value corresponds to a class of service for forwarding packets from the sender or intermediary router to the next router or receiver in the network. The forwarding behaviors can be implemented by using a variety of techniques, including priority queuing, weighted fair queuing, or conventional leaky bucket-based techniques. Relevant classes for the delivery of audio and video media streams are the Expedited Forwarding (EF) and Assured Forwarding (AF) classes, respectively. For details about the Type of Service byte, see IETF RFC 2474.

In Lync Server 2010, DSCP marking can be enabled by using Windows policy-based QoS to specify port ranges for each communication type. For operating system s that do not support policy-based QoS, you can use the DSCP marking policy in Lync Server. By default, policy-based QoS and DSCP marking are disabled.

The marked packets can then be recognized by network entities (end systems and routers) 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).

With Windows Server 2008 R2, Windows Server 2008, Windows 7, and Windows Vista, there is a new way to configure QoS profiles, called policy-based QoS. With policy-based QoS, you configure QoS policies in a Group Policy object. You can create Group Policy objects that give priority to, or manage bandwidth of, network traffic according to local application name, remote IP addresses, local/remote ports, and protocol type (UDP/TCP), and you can assign a Group Policy object to a user, group, or computer. For details about policy-based QoS, see "Overview of Policy-Based QoS" at https://go.microsoft.com/fwlink/p/?LinkId=206005.

You can enable QoS for the following Lync services, server roles, and applications:

  • A/V Conferencing service

  • A/V Conferencing Server

  • A/V Edge service

  • Application Sharing service

  • Mediation Server

  • Response Group application

  • Conference Announcement service

  • Applications based on the Unified Communications Managed API (UCMA)

You can also enable QoS for the following Lync clients. For policy-based QoS, the client must be running on the Windows 7 or Windows Vista operating system:

  • Microsoft Lync 2010

  • Microsoft Lync 2010 Attendant

  • Microsoft Lync 2010 Phone Edition

To enable QoS, perform the following tasks:

  1. Gather information for planning. Specify a nonoverlapping port range for each of the following communication types for which you want to enable QoS: audio, video, application sharing, and file transfer. By default, these port ranges do not overlap on Lync Server, but they overlap on the Lync client.

  2. Configure these port ranges on the servers and clients that will use them.

  3. For each service, server role, application, and client for which you want to enable QoS, create a Group Policy object that associates the communication type with a port range and assigns a priority to each communication type.

  4. Assign each Group Policy object to the services, server roles, applications, and clients that it will apply to.


For clients that run on operating systems other than Windows 7 and Windows Vista, policy-based QoS is not supported. You can still use QoS by modifying the Lync Server DSCP marking policy as described later in this paper.

The topics in this section explain these tasks in detail.