the RTCP packet contains below items
8 bytes of UDP header
12 bytes min of RTCP header
Variable, with 32 bit boundary of of RTCP data
RTCP is delivered over RTP UDP port number + 1
(usually one port number per multi media session)
Usually, RTCP packets are bundled and may contains several packets which is encapsulated in the same UDP data gram (to reduce the overhead due to headers)
The RTCP header has the following components
version - 2 bits
Padding bit - 1 bits
RR count - 5 bits
Packet Type - 8 bits
Message Length - 16 bits
The following are the possible packet types possible in the RTCP data
192 - FIR => Full INTRA frame request
193 - NACK => Negetive Acknowledgement
200 - SR => Sender report for transmission and reception statistics from active senders (periodically transmitted)
201 - RR => Receiver report for reception statistics from participants that are not active senders (periodically transmitted)
202 - SDES => Source Description items (including CNAME - canonical name)
203 - BYE => Good bye indicates end of participation
204 - APP => Application specific functions
207 - XR => RTCP extension
References:
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