Q. What does Server Assignment Request (SAR) achieve?
a) Triggers policy update
b) Reserves media resources
c) Allocates bearer QoS
d) Getting IFC
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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) Triggers policy update
→ Incorrect. Policy updates are typically handled by the PCRF via interfaces like Gx, not SAR.
b) Reserves media resources
→ Incorrect. Media resource reservation is managed by resource control protocols or at the bearer level, not by SAR.
c) 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) 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.
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