RFC 8866 / START HERE
SDP, before the details
SDP: Session Description Protocol
SDP is a text format describing a multimedia session, including media types, addresses, and supported formats. Despite its name, it is a description format, not the media transport itself.
The idea in one picture
An app describes media capabilities
SDP carries the description
Participants can agree on media
A simplified picture of the idea; the chapters explain the actual mechanisms.
Why it exists
Before exchanging media, participants need compatible descriptions of what they can send and receive.
A familiar example
A calling app describes an audio stream and supported codecs so another participant can select compatible settings.
Helpful background
You can start here without reading another RFC. If these ideas are unfamiliar, these short introductions may help.
What you’ll learn next
Begin with chapter one, or choose a topic.
- A description is ordered linesSDP is a structured sequence of single-letter fields, not a negotiation or transport protocol.→
- Session scope and media scopeSome session-level values apply to media descriptions unless overridden at the media level.→
- An m line describes transportThe media line declares media type, transport port, protocol, and format identifiers.→
- Time and direction are independentA session schedule and a media direction attribute answer different questions.→
- A description is not authorizationUntrusted session descriptions can direct traffic to addresses and ports the reader did not intend.→
This introduction explains RFC 8866 (2021). Read the original RFC ↗