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In Microsoft Office Communications Server 2007, Mediation Server will reject an Invite that contains a MIME message in which the Session Description Protocol (SDP) is more than two levels deep. In this case, Mediation Server generates a "488" response.
This behavior currently causes no known problems when Mediation Server interacts with Office Communications Server 2007 components on the proxy side of Mediation Server. However, it may cause problems in environments that contains new Communication Server components.
To resolve this issue, install the update package for Communications Server 2007 Mediation Server that is dated August 2008. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
952780 Description of the update package for Communications Server 2007 Mediation Server: August 2008
The next release of Office Communication Server 2007 will send Invites that contain a MIME type in which the SDP is more than two levels deep. This means that Invites that contain such a MIME type will be rejected in mixed environments that consist of Communications Server 2007 Mediation Server and new Communication Server components. A "488" response rejection means that Communications Server network components do not retry the call.
After you install this hotfix, Mediation Server returns a "415" response instead of a "488" response. The Accept header in the "415" response does not contain "multipart." Therefore, the "415" response causes the new Communications Server network components to retry the call without the MIME type.
This hotfix prevents problems in future mixed environments in which Mediation Server must interact with the new Communication Server components.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.