sr_t Struct Reference

#include <MNRTPNetTypes.h>

Collaboration diagram for sr_t:

[legend]List of all members.

Public Attributes
u_int32	ssrc
u_int32	ntp_sec
u_int32	ntp_frac
	NTP timestamp (fractions).
u_int32	rtp_ts
u_int32	psent
u_int32	osent
rtcp_rr_t	rr [1]

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Detailed Description

RTCP SR (sender report) packet.
Memory representation of an RTCP SR (sender report) packet's special part. Contained in rtcp_t. Special meanings of the common header's fields rtcp_common_t} (cut-and-paste from RFC1889):

• version: Identifies the version of RTP, which is the same in RTCP packets as in RTP data packets. The version defined by RFC1889 specification is two (2).
• p: If the padding bit is set, this RTCP packet contains some additional padding octets at the end which are not part of the control information. The last octet of the padding is a count of how many padding octets should be ignored. Padding may be needed by some encryption algorithms with fixed block sizes. In a compound RTCP packet, padding should only be required on the last individual packet because the compound packet is encrypted as a whole.
• count: The number of reception report blocks contained in this packet. A value of zero is valid.
• pt: Contains the constant 200 to identify this as an RTCP SR packet.
• length: The length of this RTCP packet in 32-bit words minus one, including the header and any padding. (The offset of one makes zero a valid length and avoids a possible infinite loop in scanning a compound RTCP packet, while counting 32-bit words avoids a validity check for a multiple of 4.)

See also:

rtcp_t

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Member Data Documentation

u_int32 sr_t::ntp_frac

NTP timestamp (fractions).

u_int32 sr_t::ntp_sec

NTP timestamp (seconds). 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 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.

u_int32 sr_t::osent

Octets sent. 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.

u_int32 sr_t::psent

Packets sent. 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.

rtcp_rr_t sr_t::rr[1]

Variable-length list of reception report blocks. 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. See also: rtcp_rr_t

u_int32 sr_t::rtp_ts

RTP timestamp. 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.

u_int32 sr_t::ssrc

Sync source identifier. The synchronization source identifier for the originator of this SR packet.

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The documentation for this struct was generated from the following file:

• MNRTPNetTypes.h

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