This specifies that the tools should be started in send-only mode. An example may be where a different unicast address is to be used for a traffic destination than for a traffic source. In such a case, two media descriptions may be used, one sendonly and one recvonly. It can be either a session- or media-level attribute, but would normally only be used as a media attribute. It is not dependent on charset. Note that sendonly applies only to the media, and any associated control protocol (e.g., RTCP) SHOULD still be received and processed as normal.