πSDP
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., itβs a request for others to send data.
Fields:
- v
protocol version (0)
- o
originator information
- s
session description
- c
connection info
- t
timestamps (NTP) for start and end of session
- m
media (type, RTP port, profile, payload types)
m=video 5004 RTP/AVP 96 97
(RTP/AVPβaudio/video profile)- a
additional attribute
- a=rtpmap:
define new RTP Payload Type (
a=rtpmap:97 H264/90000
)- a=fmtp:
format parameters (
a=fmtp:97 profile-level-id=42001f
)- a=rtcp:
set RTCP port explicitly (
a=rtcp:53020
). If not specified, RTP port+1 is assumed (RFC 3605)- a=rtcp-mux
RTP/RTCP multiplexing (same port) (RFC 5761)
- a=rtcp-rsize
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)βRTP packets are send and received on the same port (important for NAT traversal?)
See also:
Backlinks
- π SDP BUNDLE
- π Signaling
- π RTSP
- π SDP Offer/Answer model
- π WebRTC
- π Streaming