HO: If target ENB is not serviced by source MME then How source MME sends HO request?

Question

Is it possible, source eNodeB has received "handover command" message from MME and now it want to cancel handover procedure ?
What could be the possible reasons when source eNodeB want to cancel ongoing handover procedure ?

Answer 1

The S10 allows the source MME to talk with the Target MME who then forwards the message to the target eNB. The following is the path and link designation over which the message travels.

Source eNB ->S1MME-> Source MME =>S10=>Target MME -> S1MME-> Target eNB

Key - S1MME uses the S1AP protocol
- S10 Uses the GTPv2 protocol

Answer 2

When MME receives Handover required message with the target eNodeB Id which is not being served by it, it tries to get target MME which is serving to target eNodeB Id. I think it is vendor specific implementation how they manage this kind of resolutions in their network.
If source MME gets the details of target MME, it starts exchanging the handover signalling messages over the S10 link. Please go through 29.272 specification to get more details on S10 based handover signalling.