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Static and dynamic payload types

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

Learn in 5 minutes

  1. List static types 0, 8, 9, and 18 with their clocks
  2. Require rtpmap for payload types 96 through 127
  3. Refuse a G.722 clock of 16000

Visual

Static types need no guess · study drawing · cyphermonkeylabs.com AliceCarrier INVITE 100 200 ACK

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Dynamic types 96 through 127 take their meaning from rtpmap on that m-line only.

Worked example

Read static types The offer lists PCMU and PCMA on separate m-lines. Confirm the clocks are 8000.

  1. Press Negotiate.
  2. Read payload 0.
  3. Read payload 8 and its clock.

Fault

Both sides use payload type 96 and there is no audio. The rtpmap lines name different encodings.

Dynamic types match on the rtpmap encoding name, not on the number.

Quiz

Payload type 8 is


Payload type 9 is


Payload types 96 through 127


PCMU and PCMA


20 ms of G.722 advances the timestamp by


Payload type 18 is


Ecosystem

Glossary, sister systems, and the integration seam for this room.

Quality management and recording QM scores interactions. The standardized way an SBC forks a session to a recorder is SIPREC.

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