Communications Server 2007 R2 remote users cannot make public switched telephone network (PSTN) calls when Communications Server 2007 servers or proxies are in the call path

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SYMPTOMS

In Microsoft Office Communications Server 2007 R2, remote users cannot make public switched telephone network (PSTN) calls when Communications Server 2007 servers or proxies are in the call path.

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This issue occurs because Communications Server 2007 servers or proxies do not add the Record-Route header in the 183 (early media) responses. Therefore, Communications Server 2007 R2 clients cannot generate the Provisional Response Acknowledgement (PRACK) method.

Note For more information about the PRACK method, see the following Microsoft MSDN Web site:

http://msdn.microsoft.com/en-us/library/bb759215.aspx (http://msdn.microsoft.com/en-us/library/bb759215.aspx)

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RESOLUTION

To resolve this issue, install the update package for Communications Server 2007 that is dated November 2008. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

956389 (http://support.microsoft.com/kb/956389/ ) Description of the update package for Communications Server 2007: November 2008

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