3.1.5.4.3 Renegotiation of Data Collaboration Encryption

It is theoretically possible to renegotiate the encryption level in a session by sending a reINVITE message that has a different encryption level from what was negotiated when the session was created. However, renegotiation of the encryption level is not supported by the Session Initiation Protocol Extensions, and any such reINVITE SHOULD be rejected.