RTP, codecs, and DTMF

Rooms

1. The RTP header

   RTP version 2 carries a sequence number, a timestamp, an SSRC, and a marker bit. SIP does not carry those fields.

2. Static and dynamic payload types

   RFC 3551 assigns static payload types. Dynamic types are named by rtpmap, and G.722 stays at clock 8000.

3. G.711, G.729, and Opus

   Choose a codec both sides named. Read RFC 6716 and the Opus license before you draw any legal conclusion.

4. RTCP sender and receiver reports

   RTCP sender reports and receiver reports describe the RTP flow. A SIP 200 OK does not report loss.

5. telephone-event and other digit paths

   telephone-event is RFC 4733, a dynamic payload. Events 0 through 15 are DTMF. INFO and KPML are different tools.

6. ptime, packet rate, and EF

   ptime is SDP. Twenty milliseconds of G.711 is 50 packets per second and 160 bytes of payload, plus headers. Voice sits in the EF class.

7. One-way audio

   A 200 OK can be perfect while one RTP direction is missing. Read direction, c=, and who is actually sending.

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.

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