Audio callers in Microsoft Office Communications Server 2007 R2 who are located outside the corporate network firewall cannot connect to the back-office audio conference of the Microsoft Unified Communications Managed API (UCMA) 2.0 SDK's Automatic Call Distributor sample application.
This problem occurs when the application connects a remote user to an audio conference by using a back-to-back user agent. The ms-edge-proxy-message-trust header that is stamped by the Access proxy is dropped by the back-to-back user agent. This causes Focus (the active conference) to indicate that the caller is inside the corporate network. The Audio Video multipoint controller unit (AVMCU) uses this indication to decide whether to perform the Interactive Connectivity Establishment (ICE) connectivity checks. In this case, the AVMCU collects no ICE candidates when it should have. This causes the connectivity failure.
To resolve this problem, apply the following update:
974007 Description of the Cumulative Update for Office Communications Server 2007 R2, Unified Communications Managed API 2.0 Core Redist 64-bit: October 2009
To work around this problem, writers of the UCMA 2.0 application have to supply the ms-edge-proxy-message-trust header. If the header is included in the first incoming call in the FrontOfficeConversation property on the ConferenceJoinInformation object that is supplied as a parameter of the BackOfficeConversation.ConferenceSession.BeginJoin() method, Focus marks the caller as an outside caller. This causes the AVMCU to perform the ICE connectivity checks.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information about the Microsoft Unified Communications Managed API 2.0 SDK, visit one of the following Microsoft Download Center Web sites:
Microsoft Office Communications Server 2007 R2 Enterprise Edition, Microsoft Office Communications Server 2007 R2 Standard Edition, Microsoft Unified Communications Managed API Software Development Kit