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Ti+  for  TS 24.228§7.2.2§7.3.2§7.4.2
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IMS S1 signalling flow - Session Initiation: Mobile origination and termination roaming, with different network operators - IMS S1-1a. SIP INVITE request (UE1 to UE2): from UE1 to P-CSCF1
  • UE1 builds an SDP offer containing bandwidth requirements and characteristics for each set of codecs that it is capable of supporting for this session. It assigns local port numbers for each possible media flow. UE1 is willing to establish a multimedia session comprising a video stream and an audio stream. The video stream supports two codecs, either H.263 or MPEG-4 Visual. The audio stream supports the AMR codec.
  • Request-URI: contains the international E.164 number from the user.
  • Via: contains the IPv6 address or FQDN (fully qualified domain name) of the originating UE.
  • Route: Contains the P-CSCF address learnt during P-CSCF discovery, plus the elements from the Service-Route header from registration. The P-CSCF URI contains the port number learnt during the security agreement negotiation.
  • P-Preferred-Identity: The user provides a hint about the identity to be used for this session.
  • P-Access-Network-Info: The UE provides the access-type and access-info, related to the serving access.
  • Privacy: The user does not require privacy, therefore the Privacy header is set to the value "none" as specified in RFC 3325 and RFC 3323.
  • Security-Verify: Contains the security agreement as represented by the received Security-Server header.