Residual Echo Return Loss measured at this endpoint, or at the terminating endpoint of this RTP session. This relates to the echo level from the network beyond the terminating endpoint and may be interpreted as either line echo in the case of a gateway or acoustic echo in the case of a handset. Note that this echo affects conversational quality as perceived by the user at the originating end of this RTP session. A value of 127 indicates that this parameter is not available. In midpoint applications this parameter may not be available. If this is a midstream device and call quality metrics were calculated using the value of this parameter reported from the endpoint in an RTCP XR payload then the value used in this calculation MAY be reported.