LTE S1-AP handover : How does a source mme find out the target mme as part of MME relocation based handover ?

Question

As part of S1-AP procedure with MME relocation, Handover Required message sent to source MME. Target eNodeBId is present within the handover required. How source MME figure out target cell is being served by XYZ MME and sends "Forward relocation Request" message to XYZ MME.

Please provide reference also if it is there ?

Comments

Source MME selects the target MME based on the target TAI and ENb  Identity received in Handover required message..(TAI information of target MME should be configured in source MME)..

Answer 1

The source eNB forwards the decision about HO to source MME by sending the "Handover Required" message.
In this message the target eNB identity and target TAI is shared.
If there is no direct connection (like over X2 interface) the target TAI is used by source MME to facilitate the selection of a suitable target MME. (Check second link)
If the TAI is served by other MME the Forward Relocation Request message to the target MME, basicly containing the information sent to source MME in "Handover Required" message, plus information about UE Context handled by source MME.

Check here for the whole Handover procedure here
http://www.lteandbeyond.com/2012/03/s1-interface-based-handover.html

The MME selection based on TAI is in my opinion the same as the one that has place during the Initial Attach, but in this case DNS req is performed by MME not eNB. Please check here
http://www.lteandbeyond.com/2013/03/how-mme-is-selected-mme-selection-procedure.html

Comments

Thanks Bart, to share this valuable info as well as references.

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My pleasure, always here to help