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During CSFB voice call if any Packet data arrives for the UE then what will be the scenario ?

+6 votes

How Circuit Switch Fallback works?

posted May 14, 2014 by Vishal

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1 Answer

+3 votes

When CSFB is triggered, the UE is released from eNodeB and redirect to target legacy cell. while the UE continue voice call in CS side.

PS side works as following:

  1. In case of GSM or WCDMA
    the UE perform RAU procedure. EPS bearer is taken over to SGSN and converted to PDP context. Packet communication continues via GSM/WCDMA/HSPA.

  2. In case of CDMA2000 1x/HRPD
    after the UE is released from LTE, EPS bearer is preserved. Packet communication is paused in EPC side.

  • after CSFB is finished, the UE perform Cell reselection or released from legacy RAN side. come back to LTE again by TAU procedure.

  • in case of GSM/WCDMA, PDP context is taken over to MME and converted to EPS bearer. Packet communication continues.

  • in case of CDMA, preserved EPS bearer is resumed.

answer May 16, 2014 by Hiteshwar Thakur
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+4 votes

If UE doesn't have any PS session and any CSFB call initiated then UE redirected to WCDMA or GSM and after ending CS session UE moved to LTE network by performing Tracking area update.

But in case PS session is on going and CS call have to be initiated then Handover to WCDMA will be performed. But when CS call finished and PS session is also still ongoing then which procedure will be performed to move again LTE Network? If its Handover then how measurement reporting will be done.

+1 vote

I want to know what happens in the network w.r.t signalling call flow as well as user experience ?

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