IMS R1-4a. SIP 200 OK response: from S-CSCF1 to I-CSCF1

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IMS R1 signalling flow - Registration: User not registered - IMS R1-4a. SIP 200 OK response: from S-CSCF1 to I-CSCF1

S-CSCF1 sends a 200 (OK) response to I-CSCF1 indicating that Registration was successful.
S-CSCF1 inserts the Service-Route header that includes its own URI including a character string in the user part to differentiate mobile originating requests from mobile terminating requests.