What is X2-based handover with Serving GW relocation in LTE?

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 ?

Answer 1

This procedure is used to handover a UE from a source eNodeB to a target eNodeB using X2 when the MME is unchanged and the MME decides that the Serving GW is to be relocated. Following is the call flow -

Credit: http://www.lteandbeyond.com/2012/03/x2-based-handover-with-sgw-relocation.html

Comments

will you explain when S-gw changes in this scenario where mme is only one?

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I dont know the exact reason just making a Guess on what basis MME decides SGW to be changed -
1. Current SGW connected to  the eNB does not have connection with new eNB, which is in same MME pool area.
2. Load factor (less likely)