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IMS SIP Section Hub

IMS SIP Messages

IMS SIP messages are used for registration, session establishment, call progress, media negotiation, session updates, and call release in IMS networks. This page is the main hub for SIP requests, SIP responses, and procedure-based call-flow references used in VoLTE, VoNR, and IMS troubleshooting.

Primary section navigation

SIP Requests

Browse IMS SIP request methods such as REGISTER, INVITE, ACK, BYE, CANCEL, PRACK, UPDATE, MESSAGE, and REFER.

 SIP Responses

Explore SIP response codes used in IMS, including provisional, success, and failure responses for registration and call flows.

How to use this section

  • Requests initiate or modify actions.
  • Responses show progress, success, or failure.
  • Use the child index pages for message-type browsing, or the procedure groups below for practical call-flow navigation.

Browse by IMS procedure

Section overview

  • Requests page = all SIP request methods
  • Responses page = all SIP response codes
  • Procedure links = practical call-flow navigation
  • Related pages = IMS, SDP, VoLTE, VoNR, and troubleshooting references

FAQ

What are IMS SIP messages?

IMS SIP messages are the request and response transactions used for registration, call setup, session progress, media negotiation, updates, messaging, and release inside IMS-based services such as VoLTE and VoNR.

What is the difference between SIP requests and SIP responses?

Requests initiate or modify actions such as registration, call setup, update, or release. Responses show what happened to that request, including progress, success, authentication challenge, rejection, or failure.

Which SIP messages are most important in VoLTE call setup?

The most important messages are INVITE, 100 Trying, 180 Ringing, 183 Session Progress, PRACK when reliable provisional signaling is used, 200 OK, and ACK.

Why are 183 Session Progress and PRACK important in IMS?

183 Session Progress is often where early media and early-session SDP appear, while PRACK confirms reliable provisional signaling so the session can continue in a controlled way.

What is the difference between BYE and CANCEL?

BYE releases an already established dialog. CANCEL stops a pending INVITE transaction before the call setup reaches final answer.