Which interface is used in a handover between two cells managed by different MMEs?

Question

Can someone please share the MME pool concept ? How MMEs are kept in different different pools and what achieves doing so ?

Answer 1

when source eNodeB and target eNodeB is handled by different MMEs then in that case S10 interface comes into pictures. and of course both the enodeB would not have direct communication so S1 interface will involve.

Please find the call flow in the following diagram:

Source eNodeB           Source MME                         Target MME                     Target eNB
---> handover required ----->    Forward Relocation Request  ---> Handover Request     --->
<--- handover Command  <-----    Forward Relocation Response <--- Handover Request Ack  <--

Some more messages exchanged while handling handover with MME relocation.

Answer 2

In this case there should be 2 EnodeB and MME, so it will use X2/S11 interfaces.

Answer 3

The promoted answer is correct although cells can also communicate over the X2 interface, which is between eNB and eNB.

Handover over X2 is little bit less involving for Network/MMEs in signaling.