Recently, I was doing some tests with Exchange Unified Messaging, but when I tried to connect to Exchange Voice Mail using Communicator R2, I got the following error:
"Incompatible security setting. The call could not be completed because security levels do not match"
An Exchange UM dial-plan supports three different security levels: Unsecured, SIP Secured, and Secured. The following table shows the differences in terms of Mutual TLS and SRTP for the various security levels.
When integrating Exchange UM with Office Communications Server 2007, consider the following when selecting the dial plan security level:
The registry key PC2PCAVEncryption (REG_DWORD) can be used to specify whether encryption is supported, required, or not supported when making and receiving audio and video calls. The supported values are:
BTW, if you're playing around with this registry key (or any other), you may find useful to know that Communicator uses the following precedence, when applying settings:
Further investigation revealed the following error on Communicator logs:
"SIP/2.0 415 Unsupported Media Type"
After this, it seemed quite obvious that the problem had to do with encryption, more specifically to the SRTP setting. The solution? There are 2 possible ones:
One final note: the problem didn't affect Office Communicator 2007, only the R2 client, so we can assume the R2 clients will be more secure than its predecessors.