RTCP, RTP Control Protocol

Description Glossary RFCs Publications Obsolete RFCs


Protocol suite: TCP/IP.
Protocol type:Application layer protocol.
Related protocols: RTP, Real-Time Transport Protocol.
Ports:5005 (UDP).
MIME subtype:
Working groups: avt, Audio/Video Transport.
Links: IANA: RTP parameters.
RTP page at Columbia University.

MAC header IP header UDP header RTCP header Data :::

RTCP header:

0001020304050607 0809101112131415 1617181920212223 2425262728293031
Version P Count Type Length
Data :::

Version. 2 bits.
The version of RTP which is the same in RTCP packets as in RTP data packets.

P, Padding. 1 bit.
If set, this RTCP packet contains some additional padding bytes at the end which are not part of the control information. The last byte of the padding is a count of how many padding bytes 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. 5 bits. 0 to 31.
The number of reception report blocks contained in this packet.

Type. 8 bits.
RTCP packet type.

192FIR, full INTRA-frame request. RFC 2032
193NACK, negative acknowledgement. RFC 2032
194SMPTETC, SMPTE time-code mapping.RFC5484
195IJ, extended inter-arrival jitter report. RFC 5450
200SR, sender report. RFC 3550
201RR, receiver report. RFC 3550
202SDES, source description. RFC 3550
203BYE, goodbye. RFC 3550
204APP, application defined. RFC 3550
205RTPFB, Generic RTP Feedback. 
206PSFB, Payload-specific. 
207XR, RTCP extension. RFC 3611
208AVB, AVB RTCP packet.IEEE 1733
209RSI, Receiver Summary Information.RFC 5760

Length. 16 bits.
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.



[RFC 2032] RTP Payload Format for H.261 Video Streams.

[RFC 3158] RTP Testing Strategies.

[RFC 3550] RTP: A Transport Protocol for Real-Time Applications.

[RFC 3551] RTP Profile for Audio and Video Conferences with Minimal Control.

[RFC 3605] Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP).

[RFC 3611] RTP Control Protocol Extended Reports (RTCP XR).

[RFC 3711] The Secure Real-time Transport Protocol (SRTP).

[RFC 5450] Transmission Time Offsets in RTP Streams.


Obsolete RFCs:

[RFC 1889] RTP: A Transport Protocol for Real-Time Applications.

[RFC 1890] RTP Profile for Audio and Video Conferences with Minimal Control.

Description Glossary RFCs Publications Obsolete RFCs