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TS 24.228 – §6.6   List   Prev   Next
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IMS R4 Registration signalling flow - P-CSCF subscription for registration state event package - IMS R4-1a. SIP SUBSCRIBE request: from P-CSCF1 to I-CSCF1
  • From: This header is populated with the SIP URI that identifies the P-CSCF.
  • Contact: This is where the NOTIFY requests for this subscription will be sent.
  • Event: This field is set to the value 'reg' to specify the use of the reg event package.
  • I-CSCF1 sends a query to the HSS to find out the S-CSCF of the called user. The HSS responds with the address of the current S-CSCF for the terminating subscriber.