What does Server Assignment Request (SAR) achieve?

Interview
1

Q. What does Server Assignment Request (SAR) achieve?

a) Triggers policy update
b) Reserves media resources
c) Allocates bearer QoS
d) Getting IFC

Check 🔎

:arrow_right: Correct answer: Letter d.

Server Assignment Request (SAR) is a Diameter Sh-interface message used in IMS networks, sent from the S-CSCF to the HSS. Its primary function is to retrieve the Initial Filter Criteria (IFC) — a set of rules that tell the S-CSCF how to route SIP messages and which application servers to invoke for a subscriber.

Q. What does Server Assignment Request (SAR) achieve?

a) :x: Triggers policy update
→ Incorrect. Policy updates are typically handled by the PCRF via interfaces like Gx, not SAR.

b) :x: Reserves media resources
→ Incorrect. Media resource reservation is managed by resource control protocols or at the bearer level, not by SAR.

c) :x: Allocates bearer QoS
→ Incorrect. QoS allocation is the responsibility of the access and core networks (e.g., eNB, MME, PGW), not the SAR message.

d) :white_check_mark: Getting IFC
→ Correct. The SAR is used to retrieve the IFC from the HSS so the S-CSCF can trigger services correctly based on SIP message criteria. SAR/SAA update the user s S-CSCF binding and download iFCs.