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How N/W will notify to UE regarding incoming call?

+1 vote
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When UE is E-UTRAN attached, how N/W will notify the incoming call (MT call) in both RRC-Connected and RRC-Idle states?

In general, If UE is in RRC-Idle state, N/W will notify through paging message by indicating Domain as CS.
How it will happen in case when UE in RRC-Connected state?
Could anyone please explain on this?

posted May 7, 2018 by Manohar Venkat.ch

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1 Answer

+1 vote

Pre-condition: UE is registered with the network using Combined-Attach (CS and PS both) option. In combined attach, MME updates UE Location to MSC so that MSC can trigger paging for incoming CS calls.

Let's assume UE is in RRC-Connected/ECM-Connected and MME receives paging from MSC (over the SGs interface) for mobile terminating CS call. MME notifies UE by sending the CS service notification message. UE responds back by sending the extended service request message.
After that MME ask eNodeB to re-direct UE to UTRAN/GSM by sending "UE Context Modification Request" message. This message includes CS Fallback Indicator IE.
eNodeB triggers RRC connection release towards the UE with the re-direction Info and it also initiates UE Context Release procedure towards MME. MME performs RAB procedure towards SGW.

answer May 8, 2018 by Vimal Kumar Mishra
What will happen in case UE didn't perform Combined Attach?
It has to go through VoLTE option which involves SIP signalling. If both the parties are registered with their respective IMS network then both can establish VoLTE call.
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