Question

How UE latch to the UTRAN in CSFB?

Answer 1

Find the call flow below:

Step
1
UE <---> SS
< Power On >
Cell 1

2
UE <---> SS
< PRACH and RACH Response >
Cell 1

3
UE ---> SS
RRC Connection Request
Cell 1

4
UE <--- SS
RRC Connection Setup
Cell 1

5
UE ---> SS
RRC Connection Setup Complete + Attach Request + PDN Conn Req
Cell 1

6
UE <---> SS
< NAS : Security Mode Establishment >
Cell 1

7
UE ---> SS
< RRC : Security Mode Establishment >
Cell 1

8
UE <--- SS
RRC Connection Reconfiguration + Attach Accept + ...
Cell 1

9
UE ---> SS
RRCConnectionReconfigurationComplete / Attach Complete / ...
Cell 1

10
UE <---> SS
< Packet Data Transaction >
Cell 1

11
SS

LTE Network Gets CS Notification from WCDMA NW

12
UE <--- SS
CS Service Notification with Paging Identity
Cell 1

13
UE ---> SS
Extended Service Request
Cell 1

14
UE <--- SS
RRC Connection Release with Redirected Carrier Info
Cell 1

15
UE <---> SS
< RRC Connection Setup with cause of terminatingConversationCall >
Cell 2

16
UE ---> SS
Routing Area Update Request
Cell 2

17
UE <---> SS
< Authentication >
Cell 2

18
UE <---> SS
< Voice Call Setup >
Cell 2

19
UE <---> SS
< End Voice Call >
Cell 2