What is RTP on the network

RTP - Realtime Transport Protocol

Like TCP and UDP, RTP (Realtime Transport Protocol) is a transport protocol. RTP was designed by the IETF and ensures the continuous transport of data in real time. Especially for audio and video data where, depending on the codec, 1 to 20% packet loss can be tolerated. However, RTP does not guarantee the quality of service of the transmission.

Unfortunately, UDP has no functions to detect packet loss. And with TCP every lost packet has to be sent again. RTP is based on UDP so that the recipient has at least the possibility of detecting packet loss. RTP is about the fact that packet loss is acceptable to a certain extent.

The Realtime Transport Protocol (RTP) in the TCP / IP protocol stack

layerTransmission / protocol
sessionRTP
transportUDP
InternetIP (IPv4 / IPv6)
Network accessEthernet, ...

Structure of the RTP header


With RTP, the media stream is divided into data packets. Various information is contained in the header of the data packets.

  • Codec
  • Sequence number
  • time stamp
  • synchronization
  • Encryption (e.g. SRTP for VoIP)

This avoids unnecessary protocol overhead.

SRTP - Secure Realtime Transport Protocol

After the connection has been established with SIP, SIPS or H.323, the voice data is transmitted with RTP. These data packets can be recorded or cut out by a third party. As a result, the conversation connection can be eavesdropped or manipulated. The voice data is encrypted with SRTP. Eavesdropping is then no longer possible.

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