Article ID: 2251445 - View products that this article applies to.
Microsoft Unified Communications Managed API (UCMA 2.0) based trusted applications can transfer calls by using the BeginTransfer method in the Call class. In this situation, the transfer operation is unsuccessful if call authorization is performed by Office Communications Server (OCS) 2007 R2. This usually happens when the transfer target is a telephone number that is outside of the enterprise.
This issue occurs because the UCMA platform does not support the Referred-By header signing feature. OCS 2007 R2 authorizes calls to the Public Switched Telephone Network (PSTN) that results from a transfer by verifying the permissions of the transferor. This is done by verifying the Referred-By header in the Invite request. For a trusted application, this Referred-By header has to be signed by the application itself by using its certificate when the transfer operation starts. OCS 2007 R2 does not authorize calls to the PSTN if the Referred-By header is not signed or if the signature cannot be verified. Therefore, the call transfer is unsuccessful.
To fix this problem, follow these steps:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.