Audio quality gradually decreases when many users from a Public Switched Telephone Network make a conference call by using Mediation Server to connect to a CAA server in Communications Server 2007

Consider the following scenario:

• You have installed the Conference Auto Attendant (CAA) server role on a computer that is running Microsoft Office Communications Server 2007 R2.
• A conference call between many users from a Public Switched Telephone Network (PSTN) is established by using a computer that is running the Communications Server 2007 Mediation Server role to connect to the CAA server.
• The CAA server forwards the call to a computer that is running the Communications Server 2007 A\V Conferencing Server role.
• A channel for the conference call traffic is established between Mediation Server and A\V Conferencing Server.
  
  Note CAA is a new server role that is included in Communications Server 2007 R2. Mediation Server and A\V Conferencing Server are existing server roles in Communications Server 2007.

In this scenario, the audio quality gradually decreases.

This issue occurs because the Real-Time Control Protocol (RTCP) BYE packet is continuously exchanged between the A\V Conferencing Server computer and the Mediation Server computer for each user who leaves the conference call.

To resolve this issue, install the hotfix rollup package for Mediation Server that is described in the following Microsoft Knowledge Base article:

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

For more information about Communications Server 2007, visit the following Microsoft Web site: