Appendix A: Implementing in a QoS Environment
Microsoft Office Communications Server 2007 and Microsoft Office Communications Server 2007 R2 will reach end of support on January 9, 2018. To stay supported, you will need to upgrade. For more information, see Resources to help you upgrade your Office 2007 servers and clients.
If you are deploying Office Communications in an environment with existing QoS policies, Office Communications Server 2007 is designed to work within this framework. Office Communications Server applications based on synchronous traffic like audio or video streams are highly sensitive to delay, jitter and packet loss. QoS policies are typically deployed to give more bandwidth to synchronous audio and video streams compared to the asynchronous traffic like instant messaging, application sharing data or file downloads.
QoS Policy Implementations
The implementation of QoS policies in a network can be done according to several approaches such as:
Differentiated Service (DiffServ).
Integrated Services (IntServ).
Call Admission Control (CAC).
Differentiated Service (DiffServ)
Differentiated Service (DiffServ) provides a class-level prioritization based on Differentiated Services Code Point (DSCP) marking of the IP packets. See IETF RFC 2474 for a description of the 6-bit DSCP field values in the Type of Service byte of any IP packet. Each 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 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 stream are the Assured Forwarding (AH) and the Expedited Forwarding (EF) classes.
Integrated Services (IntServ)
Integrated Services (IntServ) is a framework provides strict Quality of Service guarantees and requires that routers maintain per stream state information for that purpose.
Call Admission Control (CAC)
Call Admission Control (CAC) is a framework for authorizing or rejecting calls based on available bandwidth or types of calls.
Although Office Communicator Server 2007 has been designed to work without any QoS framework, it is possible to configure the media stack to mark the IP traffic conveying the real time audio and video IP traffic according to well established classes of services.
The marking may be enabled or disabled by means of registry keys. If enabled, the marking of the IP packets is done by the QoS Packet Scheduler service. The resulting marked packets can subsequently 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 whether the audio/video traffic is delivered over the Real Time Protocol (RTP; see IETF RFC 3350) or the Secure Real Time Protocol (SRTP; see IETF RFC 3711). Because QoS policies are often tied to UDP or TCP ports, Office Communicator Server 2007 also includes a registry setting to specify the port range for the UDP and TCP ports used in delivering media streams.