Why would RTP traffic that is sent from the originating endpoint fail to be received on the far endpoint?

Why would RTP traffic that is sent from the originating endpoint fail to be received on the far endpoint?
A. The far end connection data (c=) in the SDP was overwritten by deep packet inspection in the call signaling path.
B. Cisco UCM invoked media termination point resources.
C. The RTP traffic is arriving beyond the jitter buffer on the receiving end.
D. A firewall in the media path is blocking TCP ports 16384-32768.