5.1. Retransmission Session Sharing

In the case of session-multiplexing, a retransmission session MUST map to exactly one original session; i.e., the same retransmission session cannot be used for different original sessions.

If retransmission session sharing were allowed, it would be a problem for receivers, since they would receive retransmissions for original sessions they might not have joined. For example, a receiver wishing to receive only audio would receive also retransmitted video packets if an audio and video session shared the same retransmission session.