SSRC_n (source identifier): 32 bits
The SSRC identifier of the source to which the information in
this reception report block pertains.
fraction lost: 8 bits
The fraction of RTP data packets from source SSRC_n lost since
the previous SR or RR packet was sent, expressed as a fixed
Schulzrinne, et al Standards Track [Page 25]
RFC 1889 RTP January 1996
point number with the binary point at the left edge of the
field. (That is equivalent to taking the integer part after
multiplying the loss fraction by 256.) This fraction is defined
to be the number of packets lost divided by the number of
packets expected, as defined in the next paragraph. An
implementation is shown in Appendix A.3. If the loss is negative
due to duplicates, the fraction lost is set to zero. Note that a
receiver cannot tell whether any packets were lost after the
last one received, and that there will be no reception report
block issued for a source if all packets from that source sent
during the last reporting interval have been lost.
cumulative number of packets lost: 24 bits
The total number of RTP data packets from source SSRC_n that
have been lost since the beginning of reception. This number is
defined to be the number of packets expected less the number of
packets actually received, where the number of packets received
includes any which are late or duplicates. Thus packets that
arrive late are not counted as lost, and the loss may be
negative if there are duplicates. The number of packets
expected is defined to be the extended last sequence number
received, as defined next, less the initial sequence number
received. This may be calculated as shown in Appendix A.3.
extended highest sequence number received: 32 bits
The low 16 bits contain the highest sequence number received in
an RTP data packet from source SSRC_n, and the most significant
16 bits extend that sequence number with the corresponding count
of sequence number cycles, which may be maintained according to
the algorithm in Appendix A.1. Note that different receivers
within the same session will generate different extensions to
the sequence number if their start times differ significantly.
