S3. IMS Session Initiation signalling flow —
origination in CS Network
mobile termination in home network
S3-5. SIP UPDATE request (UE1 to UE2)
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In case the IAM had contained a continuity indication, the COT message arrives to the MGCF.
When the resource reservation is completed and the possible COT message is received, MGCF sends the UPDATE request to the terminating endpoint.