RTCConfiguration - Web APIs
rtcpmuxpolicy optional the rtcp mux policy to use when gathering ice candidates, in order to support non-multiplexed rtcp.
... the value must be one of those from the rtcrtcpmuxpolicy enum.
... rtcrtcpmuxpolicy enum the rtcrtcpmuxpolicy enum defines string constants which specify what ice candidates are gathered to support non-multiplexed rtcp.

RTCPeerConnection() - Web APIs
rtcpmuxpolicy optional the rtcp mux policy to use when gathering ice candidates, in order to support non-multiplexed rtcp.
... the value must be one of those from the rtcrtcpmuxpolicy enum.

RTCPeerConnection - Web APIs
rtcrtcpmuxpolicy enum the rtcrtcpmuxpolicy enum defines string constants which specify what ice candidates are gathered to support non-multiplexed rtcp.