Which Diameter command is used by the S-CSCF to retrieve authentication vectors from the HSS?

Interview
1

Q. Which Diameter command is used by the S-CSCF to retrieve authentication vectors from the HSS?

a) RAR
b) LIR
c) MAR
d) UAR

Check 🔎

:arrow_right: Correct answer: Letter c.

The Multimedia-Authentication-Request (MAR) is the Diameter command used by the S-CSCF to obtain authentication vectors from the HSS during IMS registration.

  • It is part of the Cx interface between the S-CSCF and the HSS.
  • MAR is followed by a Multimedia-Authentication-Answer (MAA) containing the required authentication vectors (RAND, AUTN, XRES, etc.).

Q. Which Diameter command is used by the S-CSCF to retrieve authentication vectors from the HSS?

a) :x: RAR
→ Incorrect. Re-Auth-Request is related to the Gx interface (PCRF and PCEF), not used in IMS registration.

b) :x: LIR
→ Incorrect. Location-Info-Request is used by the I-CSCF to query the HSS for the user’s S-CSCF assignment, not for auth vectors.

c) :white_check_mark: MAR
→ Correct. Multimedia-Authentication-Request is used by the S-CSCF to request IMS authentication vectors from the HSS. MAR obtains IMS AKA vectors from the HSS.

d) :x: UAR
→ Incorrect. User-Authorization-Request is also used on the Cx interface but by I-CSCF for user authorization—not for retrieving authentication vectors.