Comedia - SIP:Connection-Oriented Media (Comedia)

In Asterisk:

Comedia mode means that Asterisk will ignore the IP and port in the received SDP from the peer and will wait for incoming RTP. This RTP should arrive to the port that Asterisk replied in the "200 OK" SDP. After that, Asterisk already knows where to send its RTP.
This makes communication possible with UA's behind NAT which don't solve NAT problem in client side (STUN, ICE, ALG enabled router, etc). This option works properly in conjunction with qualify=yes option in order to keep open the connection from Asterisk to the peer behind NAT.

Cisco Comedia Enhancements:

The Connection-Oriented Media (Comedia) Enhancements for SIP feature allows the gateway to check the media source of incoming Real-time Transport Protocol (RTP) packets and allows the endpoint to advertise its presence inside or outside. of Network Address Translation (NAT). Using this feature enables symmetric NAT traversal by supporting the capability. to modify and update an existing RTP session remote address and port.