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

SIP UniverseFree University

Home / SIP core: messages, transactions, dialogs / Methods and status codes

Methods and status codes

The core methods are INVITE, ACK, OPTIONS, BYE, CANCEL, and REGISTER, and status codes fall into six classes.

Learn in 5 minutes

  1. Place a code in the 1xx through 6xx classes
  2. Match ACK and CANCEL to the INVITE they belong to
  3. Separate 401 from 407

Visual

Busy is final · study drawing · cyphermonkeylabs.com UAPeer INVITE 100 180 486 ACK

SVG HTML PNG

The reason phrase is a hint. The code is the rule.

Worked example

Class the code Dissect the final response in this lab message, which is the 486.

  1. Dissect the 486.
  2. Read the CSeq.
  3. Note that a 4xx is final.

Fault

The caller hears ringing and the trace shows BYE with no To tag, then 481.

There is no confirmed dialog to end. The INVITE is still outstanding, so CANCEL matches that transaction.

Quiz

CANCEL applies to


486 Busy Here is


401 differs from 407 because


OPTIONS is used to


487 Request Terminated is the usual final response


603 Decline 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.

Glossary · Ecosystem map · Ports · Troubleshooting

Sources and go deeper