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Role of X2 interface in Handover

+2 votes

Want to know why X2 interface exist in LTE and more importantly what is the role of it in Handover process.

posted Jul 27, 2013 by Deepankar Dubey

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1 Answer

+2 votes

LTE introduces inter eNodeB interface i.e X2 in order to decongest the EPC from handover related signaling. The decongestion is significant as most of the handovers occur between enodeBs who are connected to the same MME/SGWs. X2 is comprised of controlplane(X2-AP) and data plane(X2-U).
It is also useful in,
-Direct forwarding in order to minimize data loss during the S1 handover process
-Configuration info and updates such as Served cell information, Number of Antenna Ports
-Load info such as Inter Cell Interference Coordination (ICIC)

When the user moves to the target-enb, it sends Path switch request to the MME to indicate the UEs movement. The MME sends Modify bearer req to SGW which sends End marker request to the source-enb making sure that the dataplane switch has occurred and the source-enb can release the radio resources(source-enb sends Resource release to the UE thus completing the handover.

answer Jul 27, 2013 by Chandra Javalkar
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+1 vote

In case of hub-and-spoke topology, X2 messaging can travel all the way back to an aggregation point, which may be co-located with EPC. In such scenario both X2 and S1 traverses same physical path (a.k.a X2 over S1). Please consider both Intra-MME and Inter-MME handover scenarios. Would X2 based handover in such a case yield advantage over S1 based handover. Thanks.