The a=encryption:optional tag is a Microsoft extension held over(Snom has removed it in recent beta builds I have). We do not support it and will not. Grandstream uses RTP/SAVP, Snom will be doing RTP/SAVP in 7.1.33 (in beta), Polycom does the dual m= line for RTP/SAVP and RTP/AVP. Offering crypto in an RTP/AVP is wrong please refer to RFC3711 where it clearly states "The RTP specification establishes a registry of profile names for use by higher-level control protocols, such as the Session Description Protocol (SDP), to refer to transport methods. This profile registers the name "RTP/SAVP"."
I understand. It is clear for me.
Chris,Heiko and I have had a few exchanges in email... He's a verynice guy very preceptive to the changes required to support this properly. He said he'll be trying out the two m-linemethod soon.
Great news :) Chris