Cx-Query, or Diameter UAR: User-Authorization-Request:
I-CSCF1 makes a request for information related to the Subscriber registration status by sending the
private user identity ("email@example.com"), public user identity ("firstname.lastname@example.org")
and visited domain identifier ("Visited Network Number 1") to the HSS.
Cx-Query response, or Diameter UAA: User-Authorization-Answer:
The HSS returns S-CSCF required capabilities and I-CSCF1 uses this information to select a suitable S-CSCF.