When the resource reservation is completed, UE1 sends the UPDATE request to the terminating
endpoint, via the signalling path established by the INVITE request.
Request-URI:
Takes the value of the Contact header of the received 183 Session Progress response.
Via:
Takes the value of either the IP address or FQDN of the originating UE.
CSeq:
Takes a higher value than that in the previous request.
Security-Verify:
Contains the security agreement as represented by the received Security-Server header.
SDP:
Indicates that the resource reservation was successful in the local segment.