LTE : When does eNodeB trigger handover cancel message to MME ?

Question

What could be the scenario in which source eNodeB triggers "handover cancel" procedure towards the MME ?

Answer 1

ENB can trigger HO cancel to target eNB when source eNB is performing HO preparation after getting HO meas from UE then if eNB receive A1 event from UE .

Another scenario cab be - suppose eNB has send HO command to UE and then UE is not able to perform HO complete at target eNB. Now UE comes back to source eNB by performing rrc Connection reestablishment the source eNB trigger HO cancel.

Comments

If I right, you have explained the things considering X2 connection in place between source and target eNodeB. What about when X2 connection is not available between source and target eNodeB ? I have not seen any message from MME to target eNodeB in case of handover cancel procedure ? Is it UE Context Release command or some other message that is used ?

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If HO cancel is send by source eNB to MME for HO cancel then MME sends UE Context Release to target eNB.

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Thanks to clarify my doubt.

Answer 2

It is not the normal case when source eNodeB trigger Handover Cancel towards MME for an UE. This handover cancel procedure can be initiated by source eNodeB either during the handover preparation or after the handover preparation is done but before the handover gets completed.
Source eNodeB is solely responsible to trigger this message based on the internal decision or based on the UE reported event (A1) .
I never simulated or observed this scenario is lab testing.
If someone has executed this procedure then please share the experience. This will help larger audience.