Combined attach with cause #2 (IMSI unknown in HSS)

Hello all,

I`m trying to understand the UE behavior when receiving a “Combined attach successful for EPS services only” with cause “#2 (IMSI unknown in HSS)”. This is a voice centric UE.

The UE will stay in LTE with no-CS/VoLTE services but able to use PS data? Meaning the voice domain would only work for emergency calls and regular PS data would be ok.


The UE will move to another to another RAT (3G for example) in order to fully obtain voice services since it is a voice centric UE?

Thanks for your feedback.

When Attach type only EPS, the UE initiate ESR message for CSFB tune to UTRAN for voice services.

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Will the UE normally generate voice calls, or the dial will be somehow disabled?

When CSFB enabled in network , UE will automatically switch to Voice call in legacy network to provide Voice services in both way MOC/MTC.

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Second option.

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That means there is a problem in TAC definition between eNodeB and Core side, so UE successfully attached in PS only not successfully in combined attached.

Here UE will repeat for specific times, then leave LTE toward CS domain 3G or 2G.

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