Csfb (circuit switch fall back)

CSFB CALL FLOW & BASICS

1. CSFB (CIRCUIT switch Fall Back)

2. CSFB Network Architecture UE LTE - Uu E - UTRAN MME S1 - MME UTRAN GERAN Um Uu MSC Server Iu - CS A SGs UE LTE - Uu E - UTRAN MME S1 - MME UTRAN GERAN Um Uu MSC Server Iu - CS A SGs

3. CS Call Request in E-UTRAN, Call in GERAN/UTRAN

4. Mobile Terminating call in Active Mode - PS HO supported

5. SMS over SGs is independent from CS Fallback; meaning it does not trigger CS Fallback to UTRAN or GERAN. As no fallback takes place, SMS over SGs does not require overlapped coverage of LTE and legacy technologies. CSFB SMS-MO

6. CSFB SMS MT

7. Reference(s) -: 3GPP TS 29.118 MME – Visitor Location Register (VLR) SGs Interface Specification 3GPP TS 24.301 Non-Access-Stratum (NAS) Protocol for Evolved Packet System (EPS ) 3GPP TS 23.018 Basic Call Handling 3GPP TS 23.002 LTE; Network architecture 3GPP TS 23.272 Circuit Switched Fallback in Evolved Packet System