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IMS R4 Registration signalling flow - P-CSCF subscription for registration state event package - sequence chart for IMS R4-1. SIP SUBSCRIBE request
  • This example describes the subscription procedure for the network initiated deregistration event, whereby the P-CSCF requests to be notified by the S-CSCF when the event has occurred.
  • It is assumed that the user has registered prior to initiating subscription of an event. For this example the trigger point at the P-CSCF for sending out the SUBSCRIBE request is the 200 (OK) response of the user's registration.
  • P-CSCF1 performs the DNS queries to locate the I-CSCF in the home network. The look up in the DNS is based on the address specified in the Request URI.