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RTP/RTCP
RTP Header Fields
The RTP header has the following format.
Field
Version
Padding
Extension
CSRC Count
Marker
Payload Type
Sequence Number
Timestamp
Synchronization Source (SSRC)
Identifier
Contributing Source (CSRC)
Identifier
Bit Length
Description
2
This field identifies the version of RTP. The version defined by this
specification is two (2).
1
If the padding bit is set, the packet contains one or more additional
padding octets at the end which are not part of the payload. The
last octet of the padding contains a count of how many padding
octets should be ignored.
1
If the extension bit is set, the fixed header is followed by exactly
one extension header.
4
The CSRC count contains the number of CSRC identifiers that follow
the fixed header.
1
The interpretation of the marker is defined by a profile. It is
intended to allow significant events such as frame boundaries to
be marked in the packet stream.
7
This field identifies the format of the RTP payload and determines
its interpretation by the application.
16
The sequence number increments by one for each RTP data packet
sent, and may be used by the receiver which detects packet loss
and restores packet sequence.
32
The timestamp reflects the sampling instant of the first octet in the
RTP data packet. The sampling instant must be derived from a
clock that increments monotonically and linearly in time to allow
synchronization and jitter calculations.
32
The SSRC field identifies the synchronization source. This identifier
is chosen randomly, with the intent that no two synchronization
sources within the same RTP session will have the same SSRC
identifier.
32
The CSRC list identifies the contributing sources for the payload
contained in this packet. The number of identifiers is given by the
CC field.
86
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