RTCP

RTCP provides the out-of-band control stream for RTP, delivering essential QoS feedback and participant synchronization for real-time media.

Defined in RFC 3550, the Real-time Transport Control Protocol (RTCP) acts as the diagnostic engine for VoIP and video streaming. It works alongside RTP (usually on the next consecutive UDP port) to monitor data delivery and provide reception statistics like packet loss, jitter, and round-trip time (RTT). By exchanging Sender Reports (SR) and Receiver Reports (RR), it allows endpoints to scale bitrates dynamically and synchronize audio and video streams using NTP timestamps. It is the industry standard for maintaining call quality in environments ranging from Zoom meetings to enterprise-grade SIP trunks.

https://datatracker.ietf.org/doc/html/rfc3550