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SIP call setup with authentication

This call flow shows the SIP call setup between a SIP client ( and a SIP server ( The flow also shows the RTP message flow between the SIP client and the Media Gateway (
The example covers the following:

  1. SIP invite from the client.
  2. The SIP server challenges the client to authenticate.
  3. The client responds to the authentication challenge.
  4. The call is connected.
  5. The call enters the conversation phase with RTP traffic.
  6. The SIP call is cleared.

SIP call flow with authentication

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Voice Over LTE (VoLTE) Originating Call

Voice over LTE (VoLTE) is the standard for voice call setup in LTE networks. When VoLTE is deployed, phones will not need to fallback to 3G for voice calls.

VoLTE uses IMS SIP signaling to set up voice calls. The following VoLTE call flow describes the IMS call setup and release. An example of sending an SMS over IMS is also included. Sample RTP and RTCP messages are also shown in the flow.
Voice over LTE Call Flow

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IMS registration sequence diagram

This sequence diagram details the message interactions involved in IMS registration. IMS registration from a visited IMS network is covered. The interactions covered are:

  • Terminal attaching to the GPRS Network.
  • Terminal activates a PDP context.
  • An unauthenticated IMS registration is attempted.
  • IPSec security association is established between the User terminal and the P-CSCF.
  • Finally the terminal performs an IPSec protected registration that completes the authentication of the network and the terminal.

IMS registration sequence diagram