Question

Is it mandatory that X2 connection established between cell have single MME ? ie If enb X is connected with mme 1 and other eNB Y is connected with MME2 then Is X2 possible between mme1 and mm2?

Answer 1

If x2 is available between two eNBs and both eNBs are connected with different MMEs then S1 HO will be performed and data forwarding will be done via direct tunneling (via x2).

Comments

Thanks for sharing your answer.

Answer 2

If handover is being supported between any two eNodeBs over the X2 link, it is mandatory for both the eNodeBs to be connected to same MME in order to support the change data path direction from SGW to new eNodeB.
If handover is not mandatory for the X2 link then it is not necessary that both eNodeB should have connection with same MME.

Comments

Hi Harshita,
Thanks for response Harshita.  
How data path will impact If enb X is connected with MME 1 and other eNB Y is connected with MME2 There is X2 link between eNB1 and eNB2.
Since, mme can communicate with other mme through  s10 interface.

Please, explain in detail if possible

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Hi Rakesh, I mentioned in my first sentence that if X2 handover is being supported between two eNodeBs then only it is required for both eNodeBs to be connected to same MME. The reason behind is "X2 handover signalling between eNodeBs is unknown to MME". If SGW is not updated with the new target eNodeB downlink tunnels, downlink data will keep delivering to source eNodeB which is incorrect. To update the downlink tunnels at SGW, target eNodeB sends "S1-AP Path switch request to MME" after handover completion. During the handover execution, forwarded tunnels will be used to forward data from source eNodeB to target eNodeB.