Registering Values of the SDP 'proto' Field for Transporting RTP Media over TCP under Various RTP Profiles
Extracted elements (13)
The new SDP transport protocol identifiers are primarily intended for use by the SDP offer/answer model (RFC3264) to negotiate and establish RTP-based media over TCP. The existing protocol identifier set lacked entries for the combination of TCP transport with the various RTP security and feedback profiles, motivating these registrations.
All seven new TCP-based RTP transport identifiers uniformly use the RFC4571 framing method for encapsulating RTP/RTCP (and STUN in the ICE case) over connection-oriented TCP, ensuring a consistent framing baseline across all profile variants.
When ICE TCP candidates are set up per RFC6544, the RFC4571 framing mechanism MUST be used for framing STUN packets (for keepalives and consent checks), as defined in Section 3 of RFC6544.
TCP/DTLS/RTP/SAVP describes Secure RTP (RFC3711) using DTLS-SRTP (RFC5764) over TCP. Key establishment follows RFC5764 procedures and framing follows RFC4571 for transporting DTLS-SRTP packets over TCP.
TCP/DTLS/RTP/SAVPF describes Secure RTP with RTCP-based feedback (RFC5124) using DTLS-SRTP over TCP. Key establishment follows RFC5764 and framing follows RFC4571.
TCP/RTP/AVPF describes RTP media with RTCP-based feedback (RFC4585) over TCP. The RTP/AVPF stream is realized using the RFC4571 framing method.
TCP/RTP/SAVP describes Secure RTP (SRTP, RFC3711) media over TCP. The RTP/SAVP stream is realized using the framing method defined in RFC4571.
TCP/RTP/SAVPF describes Secure RTP media with RTCP-based feedback (RFC5124) over TCP. The RTP/SAVPF stream is realized using the framing method defined in RFC4571.
TCP/TLS/RTP/AVP describes RTP media on top of TLS over TCP. RTP/AVP packets are framed using RFC4571 and transported as TLS application data messages per the RFC4572 TLS association setup procedures.
TCP/TLS/RTP/AVPF describes RTP media with RTCP-based feedback (RFC5124) on top of TLS over TCP. Packets are framed per RFC4571 and transported over a TLS association established per RFC4572.
The SDP 'm=' line specifies transport protocol via the 'proto' field. This document defines seven new 'proto' identifiers for transporting RTP media over TCP: TCP/RTP/AVPF, TCP/RTP/SAVP, TCP/RTP/SAVPF, TCP/DTLS/RTP/SAVP, TCP/DTLS/RTP/SAVPF, TCP/TLS/RTP/AVP, and TCP/TLS/RTP/AVPF.
IANA registered seven new 'proto' identifiers in the 'proto' subregistry of the 'Session Description Protocol (SDP) Parameters' registry: TCP/RTP/AVPF, TCP/RTP/SAVP, TCP/RTP/SAVPF, TCP/DTLS/RTP/SAVP, TCP/DTLS/RTP/SAVPF, TCP/TLS/RTP/AVP, and TCP/TLS/RTP/AVPF, all referencing RFC 7850.
The new 'proto' identifiers do not introduce additional security considerations beyond those specified by the individual transport protocols they identify and those detailed in Section 7 of RFC4566 (SDP). Security properties are inherited from the underlying transport (TLS, DTLS-SRTP, SRTP) referenced in each identifier.