RTP Protocol Référence
Référence pour Real-time Transport Protocol: packet formater, payload types, et RTCP feedback.
Packet Format
RTP (RFC 3550) carries real-time media over UDP. The 12-byte header contains version, padding, extension, CSRC count, marker, payload type, sequence number, timestamp, and SSRC. The payload type identifies the codec (e.g., 0 for PCMU/G.711). Sequence numbers detect packet loss and reorder. Timestamps convey sampling time for jitter buffer and synchronization. SSRC identifies the synchronization source. CSRC lists contributing sources for mixers.
- payload type
- Codec identifier
- timestamp
- Sampling time
- SSRC
- Source identifier
0=PCMU, 8=PCMAjitter buffer32-bit randomRTCP and Extensions
RTCP (RTP Control Protocol) provides feedback on quality, packet loss, and jitter. Sender Reports (SR) and Receiver Reports (RR) convey statistics. NACK, FIR, and PLI messages request retransmission or keyframes. RTP extensions (header extensions) carry additional metadata like audio levels or orientation. RFC 5285 defines one-byte and two-byte extension headers. SFUs (Selective Forwarding Units) route RTP without mixing. Simulcast sends multiple quality layers.
- RTCP
- Quality feedback
- extensions
- Header extensions
- simulcast
- Multiple layers
SR, RR, NACKRFC 5285adaptive quality