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SDP and offer/answer
How to read an SDP body, and how RFC 3264 matches offers to answers without reordering streams.
7 rooms42 quiz items
Rooms
- The lines in an SDP body
Read v, o, s, c, t, m, and a lines as a session description. RFC 8866 is the current SDP specification.
- Same m-lines, same order
RFC 3264 matches streams by position. The answer has the same number of m-lines, in the same order.
- rtpmap names and fmtp parameters
Match codecs by the rtpmap encoding name. The G.722 rtpmap clock stays 8000.
- Direction attributes and hold
sendrecv, sendonly, recvonly, and inactive are per stream. Hold is commonly sendonly or inactive.
- Port 0 rejects a stream
Port 0 refuses the stream in that slot. The m-line stays, with a protocol and a format list.
- Early media and 183
183 Session Progress with SDP is the usual early-media pattern. 180 means ringing. A 183 does not always have SDP.
- Offer/answer pitfalls in RFC 6337
RFC 6337 is the usage document for offer/answer mistakes: order, version, delayed offer, and hold.
Ecosystem
SIP does not replace workforce management, quality monitoring, CRM, emergency policy, or a messaging registry. It is the session seam those systems hang from. Compliance notes on this page are educational and are not legal advice.