Description
The Real-time Transport Control Protocol (RTCP) operates in conjunction with the Real-time Transport Protocol (RTP) to manage the delivery of real-time data like audio and video over IP networks. While RTP handles the actual media payload transmission, RTCP uses separate, periodic control packets sent to all participants in a session. These packets carry sender and receiver reports that contain vital statistics such as packet count, octet count, jitter, round-trip time, and packet loss fraction. This feedback allows applications to monitor the quality of service (QoS) and network congestion, enabling adaptive mechanisms like codec switching or bitrate adjustment. RTCP also carries source description items (SDES), including the canonical name (CNAME) for participant identification, which is crucial for synchronizing multiple media streams (e.g., audio and video from the same source) across different RTP sessions. Furthermore, RTCP can convey bye packets for session termination and application-defined packets for extended control. The protocol is designed to scale by dynamically adjusting the reporting interval based on the number of session participants to prevent control traffic from overwhelming the network; typically, RTCP traffic is limited to 5% of the total session bandwidth. In 3GPP architectures, especially for IMS-based services like VoLTE, RTCP reports are used by the UE and network elements to assess bearer quality and may trigger radio layer adjustments or codec mode requests. The protocol is defined by the IETF in RFC 3550, and 3GPP profiles its use, specifying mandatory support for certain report types and the Secure RTCP (SRTCP) extension for confidentiality and message authentication in media planes.
Purpose & Motivation
RTCP was created to address the lack of feedback and control mechanisms in real-time data delivery using RTP. Pure RTP provides no inherent way for senders to know if receivers are getting the stream, or for receivers to report on network conditions like loss and delay. This made it difficult to implement adaptive streaming, diagnose problems, or manage multi-party sessions. RTCP solves these problems by providing a standardized, low-overhead control channel. Its primary purposes are QoS monitoring, allowing endpoints to adapt to network conditions; media synchronization, using the CNAME identifier; and minimal session management. In the context of 3GPP, the adoption of RTCP was motivated by the need for carrier-grade telephony over IP (VoIP), where monitoring call quality is essential for service assurance and user experience. It provides the technical means for the network and devices to implement quality reporting features mandated by regulatory or service-level requirements.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (68 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-5, normative work from Rel-15.
In Release 15, the RTCP function was enhanced to support multi-talker scenarios, introducing new floor control server procedures towards the participant and updates for non-controlling MCPTT functions. These changes included the coding of floor control messages to support functional aliases and updates to the QoS Notification Control description and data model. Furthermore, the release updated the floor control server state transition diagram for general floor control operation.
- Multi-Talker floor control server TS 24.380CR0178
- Mutli-talker – floor control towards the participant TS 24.380CR0179
- Updates to Non-controlling MCPTT function for Multi Talker TS 24.380CR0183
- Floor Control Server towards participant TS 24.380CR0187
- Coding of floor control messages to support functional alias TS 24.380CR0192
- Procedures for floor control messages to support functional alias TS 24.380CR0193
+ 2 more changes
In Release 16, the RTCP function was enhanced to support the transport of Time-Sensitive Networking (TSN) information and TSC assistance information between the Policy Control Function (PCF) and the Application Function (AF). Additionally, specific procedures were corrected and refined, including Off-Network and On-Network Floor Control procedures, and support for RTCP flows was added in IMS-related P-CSCF procedures.
- IMS related P-CSCF procedures, support of RTCP flows TS 29.514CR0120
- Transport of TSN information and containers between PCF and AF TS 29.514CR0145
- Transport of TSC assistance information between PCF and AF TS 29.514CR0146
- Incorrect reference to table for MBMS Subchannel Control TS 24.581CR0038
- Minor corrections in transmission control state machine TS 24.581CR0066
- New instance creation and release for basic / general reception control state m/c. TS 24.581CR0073
+ 9 more changes
In Release 17, specific corrections and updates were made to RTCP-based floor control procedures for mission-critical services. These included corrections to the floor indicator for On-Network Floor Control, handling of messages for upgrading or downgrading a broadcast call, and updates to the floor control server state transition diagram for basic operations. Additionally, corrections were made for scenarios involving call setup over a pre-established session and for floor control when groups are regrouped.
- Support of e2ae security using DTLS-SRTP for non WebRTC sessions TS 23.334CR0178
- MCVideo Functional Alias usage in Transmission Control TS 24.581CR0079
- Support of e2ae security using DTLS-SRTP for non WebRTC sessions TS 29.334CR0148
- AF Session for control of MPS for DTS TS 29.514CR0293
- Slice data rate control in N5 interface TS 29.514CR0366
- Corrections to floor indicator of On-Network Floor Control procedures TS 24.380CR0274
+ 9 more changes
In Release 18, key RTCP-related enhancements focused on supporting multiplexing for Mission Critical services over 5G Multicast/Broadcast Service (5MBS). Specifically, the release introduced clarified rules for using Synchronization Sources (SSRCs) in RTCP signaling, as well as for RTP audio and RTCP floor control streams in MCPTT, and for RTP media and RTCP transmission control streams in MCVideo, when these streams are multiplexed over a 5MBS channel.
- Add timers and counters in the participating MCPTT function for MBS channel control TS 24.380CR0347
- MCPTT support of multiplexing - SSRC used in RTCP signalling over 5MBS TS 24.380CR0363
- MCPTT support of multiplexing - SSRCs used for RTP audio and RTCP floor control TS 24.380CR0356
- Add timers and counters in the participating MCVideo function for MBS channel control TS 24.581CR0111
- MCVideo support of multiplexing - SSRCs used for RTP media and RTCP transmission control TS 24.581CR0117
- MCVideo support of multiplexing - SSRC used in RTCP signalling over 5MBS TS 24.581CR0122
+ 15 more changes
In Release 19, the RTCP function was enhanced to support IMS restoration procedures after PCRF/PCF failure by adding a trigger procedure for RTCP Receiver Report (RR) packets. Furthermore, support was added for reporting network Quality of Service (QoS) monitoring control and for conveying QoS notification control information in both uplink and downlink directions.
- Add RTCP RR packets trigger procedure to support IMS restoration procedures after PCRF/PCF failure TS 23.334CR0186
- [5G_RTP_Ph2] RTCP SDES Item for MID TS 26.522CR0020
- Add RTCP RR packets trigger procedure to support IMS restoration procedures after PCRF/PCF failure TS 29.334CR0419
- Report of network support of Qos Monitoring control TS 29.514CR0664
- QoS notification control in UL and DL direction information TS 29.514CR0768
- RAN-Controlled UL Bitrate Recommendation Indication TS 29.514CR0809
+ 3 more changes
Explore further
Broader topics and technologies where RTCP plays a role.
Defining Specifications
3GPP specifications that define or reference RTCP, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 23.333 vj00 | MRFC-MRFP Mp Interface Requirements | Rel-19 |
| TS 23.334 vj00 | IMS-ALG to IMS-AGW Interface (Iq) Stage 2 | Rel-19 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 24.380 vj10 | MCPTT Media Plane Control Protocol | Rel-19 |
| TS 24.581 vj00 | MCVideo Media Plane Control Protocol Specification | Rel-19 |
| TS 25.410 vj00 | Iu Interface Introduction for UTRAN | Rel-19 |
| TS 25.414 vj00 | UTRAN Iu Interface User Plane Transport Protocols | Rel-19 |
| TR 25.993 vj00 | UTRA RAB Examples and Radio Interface Mapping | Rel-19 |
| TS 26.114 vj10 | IMS Multimedia Telephony Media Handling | Rel-19 |
| TS 26.234 vj00 | 3GPP PSS Protocols and Codecs Specification | Rel-19 |
| TS 26.235 vc00 | Default Codecs for 3GPP IP Multimedia Subsystem | Rel-12 |
| TS 26.281 vj00 | MCVideo Codecs and Media Handling | Rel-19 |
| TS 26.348 vj00 | xMB Interface Specification | Rel-19 |
| TS 26.522 vj30 | RTP for XR in 5G Systems | Rel-19 |
| TS 26.804 vj10 | 5G Media Streaming Extensions Study | Rel-19 |
| TS 26.822 vj20 | 5G RTP Configurations Study Phase 2 | Rel-19 |
| TS 26.880 ve00 | MBMS Enhancements for Mission Critical Video | Rel-14 |
| TR 26.902 vj00 | Video Codec Performance for 3GPP Packet Services | Rel-19 |
| TR 26.910 vj00 | MTSI enhancements for RAN delay budget reporting | Rel-19 |
| TR 26.923 vj00 | Study on IMS-based Telepresence Media Handling | Rel-19 |
| TR 26.924 vj00 | MTSI QoS Improvement Study | Rel-19 |
| TR 26.926 vj00 | Traffic Models & Quality Evaluation for Media/XR in 5G | Rel-19 |
| TR 26.935 vj00 | Speech Codec Performance for Packet Switched Multimedia | Rel-19 |
| TR 26.937 vj00 | 3GPP PSS Characterization | Rel-19 |
| TR 26.962 vj00 | ITT4RT Operation and Usage Guidelines | Rel-19 |
| TS 29.162 vj00 | IMS-IP Network Interworking | Rel-19 |
| TS 29.163 vj00 | Interworking between 3GPP IM CN and CS networks | Rel-19 |
| TS 29.238 vj00 | H.248 Profile for IBCF-TrGW Interface | Rel-19 |
| TS 29.292 vj00 | IMS Centralized Services (ICS) Interworking | Rel-19 |
| TS 29.332 vj00 | MGCF-IM-MGW Interface Protocol (Mn) | Rel-19 |
| TS 29.334 vj00 | IMS-ALG to IMS-AGW Interface Protocol | Rel-19 |
| TS 29.380 vj00 | MCPTT-LMR Interworking Media Plane Control | Rel-19 |
| TS 29.414 vj00 | Nb Interface Bearer Transport & Control Protocols | Rel-19 |
| TS 29.424 v801 | H.248 Profile for Trunking Media Gateways | Rel-8 |
| TS 29.514 vj40 | 5G System; Policy Authorization Service; Stage 3 | Rel-19 |
| TS 29.582 vj00 | MCData Interworking with LMR Systems | Rel-19 |
| TS 29.866 vj00 | IMS Disaster Prevention & Restoration Enhancement | Rel-19 |
| TS 33.303 vj00 | ProSe Security Specification for EPS | Rel-19 |
| TS 33.879 vd10 | MCPTT Security Study | Rel-13 |
| TS 34.229 vj21 | IMS SIP/SDP UE Conformance Testing for 5GS | Rel-19 |
| TS 36.750 ve10 | Study on enhancement of VoLTE | Rel-14 |
| TS 37.579 vi40 | Mission Critical services conformance testing | Rel-18 |
| TS 43.318 vj00 | Generic Access Network (GAN) Stage 2 | Rel-19 |
| TR 43.901 vj00 | Generic Access to A/Gb Interface Feasibility Study | Rel-19 |
| TR 43.902 vj00 | GAN Enhancements Feasibility Study | Rel-19 |
| TS 44.318 vj00 | Generic Access Network (GAN) Interface Procedures | Rel-19 |
| TS 48.103 vj00 | A Interface User Plane Transport Protocols | Rel-19 |