SDP = Session Description Protocol. RFC 4566 (2006).
SDP is a textual format to describe sessions (usually RTP).
SDP usually refers to what participant is expected to receive. i.e., it’s a request for others to send data.
- protocol version (0)
- originator information
- session description
- connection info
- timestamps (NTP) for start and end of session
- media (type, RTP port, profile, payload types)
m=video 5004 RTP/AVP 96 97(RTP/AVP—audio/video profile)
- define new RTP Payload Type (
- format parameters (
- set RTCP port explicitly (
a=rtcp:53020). If not specified, RTP port+1 is assumed (RFC 3605)
- RTP/RTCP multiplexing (same port) (RFC 5761)
Reduced-Size RTCP (RFC 5506)
- drop some fields, making packets smaller, so there is higher chance they are delivered
- should be used with RTP/AVPF (RTP Profile for RTCP-based feedback) RFC 4585
- a=recvonly, a=sendonly, a=sendrecv
intention (RFC 4566). usage in SDP negotiation (RFC 3264)
- sendrecv is the default value
Symmetric RTP (RFC 4961)—RTP packets are send and received on the same port (important for NAT traversal?)