2.2.11.1 RTCP Profile Specific Extension for Estimated Bandwidth

The format of the RTCP profile specific extension for estimated bandwidth is as follows.

Type (2 bytes): The extension type. Set to 0x0001 (1).

Length (2 bytes): The extension length in bytes, including this header. Set to 0x000C (12) or 0x0010 (16).

SSRC (4 bytes): The SSRC for which the bandwidth estimated is being reported.

Bandwidth (4 bytes): The estimated bandwidth in bits per second. A value of 0xFFFFFFFD (-3) means that this host does not yet have enough measurements to generate a bandwidth estimate and it also indicates the host supports packet pair receiving. A value of 0xFFFFFFFB (-5) means the host supports packet train receiving and it does not have enough measurements to generate a bandwidth estimate<22>. A value of 0xFFFFFFFA (-6) means this host supports packet train receiving and it signals the remote host to send packet train whenever possible<23>.

Confidence Level (4 bits) <24>: The confidence level of the bandwidth. A value of 0 means the estimated bandwidth is of the lowest confidence or least reliable. A value of 15 means the estimated bandwidth is of the highest confidence or most reliable. A larger confidence level value indicates a more reliable estimated bandwidth.

Reserve1 (4 bits): Reserved for future use. The sender SHOULD set it to 0. The receiver MUST ignore it.

Reserve2 (1 byte): Reserved for future use. The sender SHOULD set it to 0. The receiver MUST ignore it.

Reserve3 (2 bytes): Reserved for future use. The sender SHOULD set it to 0. The receiver MUST ignore it.

The last 4 bytes include the Confidence Level field, which is optional. The presence of the last 4 bytes MUST be consistent with the Length field. A length of 0x000C (12) indicates the last 4 bytes is not present. Length of 0x0010 (16) indicates the last 4 bytes is present. If the Confidence Level field is not present, then the confidence level of the estimated bandwidth SHOULD be treated as unknown.