A student's open lab: learning and sharing, free for everyone.

SIP UniverseFree University

Home / SDP and offer/answer / The lines in an SDP body

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.

Learn in 5 minutes

  1. Name the session lines and the media lines
  2. State that RFC 8866 obsoletes RFC 4566 and where status is decided
  3. Separate the connection address from the RTP packets

Visual

SDP rides inside the INVITE · study drawing · cyphermonkeylabs.com AliceSBCCarrier INVITE 100 INVITE 200

SVG HTML PNG

Session lines apply until an m-line starts a stream. Media lines and their a-lines belong to that stream.

Worked example

Point at c= and m= Dissect the INVITE and find the connection line and both media lines.

  1. Press Dissect.
  2. Find c=.
  3. Count the m= lines and read each port.

Fault

The INVITE is present and the listener still hears silence.

SDP names the RTP destination. Silence means those packets are not in the capture.

Quiz

Which RFC is the current SDP specification?


What does the c= line name?


An a= line placed after an m= line applies to


The documentation addresses in these labs come from


o= includes


SDP itself carries


Ecosystem

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

Workforce management WFM forecasts volume and builds schedules. It consumes contact-center events. It does not parse Via headers. When a forecast is wrong, the SIP symptom is usually queue delay and 480 or carrier congestion, not a broken dialog ID.

Glossary · Ecosystem map · Ports · Troubleshooting

Sources and go deeper