RealTime Control Protocol

from Wikipedia, the free encyclopedia

The Real Time Control Protocol ( RTCP , and RTP Control Protocol called) the negotiation and compliance functions of parameters of quality of service (Engl. Quality of Service, QoS) by the periodic exchange of control messages between sender and receiver. A

  1. Feedback of the previously provided quality of service, whereby an adaptation of the data transmission rate can take place;
  2. Identification of all session participants, whereby semantically coherent but separately sent media streams can be synchronized;
  3. Control of the data transmission rate used for RTCP packets so that the exchange of RTCP messages does not interfere with the transmission, which could happen in sessions with many participants.

The RealTime Control Protocol is used together with the Real-Time Streaming Protocol (RTSP), which is responsible for controlling the transmission, and the Real-Time Transport Protocol (RTP), which is responsible for the actual transmission .

Typically, RTCP is based on the User Datagram Protocol (UDP) as the transport protocol. The port number used is not statically fixed, but is determined anew for each RTP session. RTP uses an even port number and RTCP the following uneven port number.

RTCP header

Byte 0 Byte 1 Byte 2 Byte 3
Bit 0 1 2 3 4th 5 6th 7th Bit 0 1 2 3 4th 5 6th 7th Bit 0 1 2 3 4th 5 6th 7th Bit 0 1 2 3 4th 5 6th 7th
V = 2 P RC PT Length
Version (V), 2 bit
Version status of the RTCP protocol (currently V.2)
Padding (P), 1 bit
The fill bit is set if one or more fill octets are appended to the end of the packet that do not belong to the actual data content (payload). The last fill octet indicates the number of fill octets added. Fill octets are only required if subsequent protocols require a specified block size, e.g. B. Encryption Algorithms.
Report Counter (RC), 5 bit
Indicates the number of reports contained in this package.
Packet Type (PT), 8 bit
This field describes the format of the RTCP packet.
Type abbreviation ID
Sender report SR 200
Receive report RR 201
Source Description SDES 202
Goodbye (end of participation) BYE 203
Application defined APP 204
Length, 16 bit
This field describes the length of the entire RTCP packet.

See also

Individual evidence

  1. RFC 3550 : RTP: A Transport Protocol for Real-Time Applications. Chapter 6: RTP Control Protocol - RTCP

Web links

  • RFC 3550 - RTP: A Transport Protocol for Real-Time Applications
  • RFC 3556 - Session Description Protocol (SDP) Bandwidth modifiers for RTP Control Protocol (RTCP) Bandwidth
  • RFC 3605 - Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP)
  • RFC 3611 - RTP Control Protocol Extended Reports (RTCP XR)
  • RFC 4585 - Extended RTP Profile for Real-time Transport Control Protocol (RTCP) -Based Feedback (RTP / AVPF)
  • RFC 5506 - Support for Reduced-Size Real-Time Transport Control Protocol (RTCP): Opportunities and Consequences