R4. IMS Registration signalling flow —
P-CSCF subscription for registration state event package
R4-3a. SIP NOTIFY request:
from S-CSCF1 to P-CSCF1
(8 of 10)
: The tag of this field matches that of the "To" field in the received 200 (OK) response for the SUBSCRIBE request.
: Set to the value of the Accept header received in the SUBSCRIBE request or "application/reginfo+xml" if the Accept header was not present in the SUBSCRIBE request.