NTP timestamp: 64 bits
Indicates the wallclock time when this report was sent so that
it may be used in combination with timestamps returned in
reception reports from other receivers to measure round-trip
propagation to those receivers. Receivers should expect that the
measurement accuracy of the timestamp may be limited to far less
than the resolution of the NTP timestamp. The measurement
uncertainty of the timestamp is not indicated as it may not be
known. A sender that can keep track of elapsed time but has no
notion of wallclock time may use the elapsed time since joining
Schulzrinne, et al Standards Track [Page 24]
RFC 1889 RTP January 1996
the session instead. This is assumed to be less than 68 years,
so the high bit will be zero. It is permissible to use the
sampling clock to estimate elapsed wallclock time. A sender that
has no notion of wallclock or elapsed time may set the NTP
timestamp to zero.
RTP timestamp: 32 bits
Corresponds to the same time as the NTP timestamp (above), but
in the same units and with the same random offset as the RTP
timestamps in data packets. This correspondence may be used for
intra- and inter-media synchronization for sources whose NTP
timestamps are synchronized, and may be used by media-
independent receivers to estimate the nominal RTP clock
frequency. Note that in most cases this timestamp will not be
equal to the RTP timestamp in any adjacent data packet. Rather,
it is calculated from the corresponding NTP timestamp using the
relationship between the RTP timestamp counter and real time as
maintained by periodically checking the wallclock time at a
sampling instant.
sender's packet count: 32 bits
The total number of RTP data packets transmitted by the sender
since starting transmission up until the time this SR packet was
generated. The count is reset if the sender changes its SSRC
identifier.
sender's octet count: 32 bits
The total number of payload octets (i.e., not including header
or padding) transmitted in RTP data packets by the sender since
starting transmission up until the time this SR packet was
generated. The count is reset if the sender changes its SSRC
identifier. This field can be used to estimate the average
payload data rate.
The third section contains zero or more reception report blocks
depending on the number of other sources heard by this sender since
the last report. Each reception report block conveys statistics on
the reception of RTP packets from a single synchronization source.
Receivers do not carry over statistics when a source changes its SSRC
identifier due to a collision. These statistics are:
