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How MME notify to LTE UE for CS call to perform CSFB when UE is in connected mode or idle mode?

+1 vote

Suppose MME is getting CS call notification for MSC then How MME will notify to UE when
1. UE is idle mode. ?
2. UE is in connected mode?

posted May 29, 2015 by Veer Pal Singh Yadav

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2 Answers

+2 votes
Best answer

1) UE is in Idle Mode: First send the Paging with CN Domain : CS. After that UE will send the RRC Request then try to send the CS Service Notification for MT CSFB Call.

2)UE is in connected mode? : If UE is already in Connected Mode there is no need of paging. Just directly send CS Service Notification Message to Initiate a MT CSFB Call.

answer Jun 2, 2015 by Anand Yadav
+2 votes

There are two different scenario when UE is in ECM-CONNECTED and another state i.e. ECM-IDLE.
- when UE is in ECM-CONNECTED (UE is registered and holds radio connection with eNodeB), MME sends UE Context Modification Request message with "CS Fall back Indicator" to eNodeB for particular UE . On receiving "UE Context Modification Request" message, eNodeB issues RRC connection release with "redirected carrier info".

  • When UE is ECM-IDLE state (state when UE doesn't have rrc connection with eNodeB), MME issues paging message for UE with CS indicator. On receiving paging message, UE initiates "Extended Service Request" towards MME and MME sends "CSFB indicator" in Initial Context Setup Request message to eNodeB and ask re-direct to UE.
answer May 30, 2015 by Vikram Singh
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+3 votes

What happens for an UE at MME, which gets triggered "UE Context Modifcation Procedure" for "CS fall back" ?

+3 votes

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At this point, does the HSS sends CANCEL-LOCATION (CLR Diameter s6a) to the MME?

In the same context, when the UE returns to LTE, does the MME set the "Skip Subscriber Data" flag (part of the ULR flags to indicate that the HHS may skip the subscription data in the ULA?