This post will introduce the difference between the inter-eNodeB handover and the intra-eNodeB handover.
Firstly, the key information elements in the inter-eNodeB handover signaling procedure are the same as those in the intra-eNodeB handover signaling procedure.
Compared with intra-eNodeB handovers, inter-eNodeB handovers use handover request and acknowledgment messages between the source eNodeB and eCNS and between the target eNodeB and eCNS.
The source eNodeB transmits the Handover Required message to the eCNS. The message carries information such as MME UE S1AP ID, eNB UE S1AP ID, Handover Type, Cause, Source ID, Target ID, and Intra-LTE HO Information ListRequest (Source eNodeB to Target eNodeB Transparent Container).
The target eNodeB receives the Handover Request message from the eCNS. The message is reassembled and transmitted by the eCNS. After the message is received, the target eNodeB is triggered for handover preparation. For example, new SAE bearers are established in a new cell for the user.
The target eNodeB performs admission control first and then transmits the Handover Request Acknowledge message to the eCNS based on the EPS bearer information after the L1 or L2 configuration is complete. The key IE in the message is Intra-LTE HO Information ListResponse in which the Target eNodeB to Source eNodeB Transparent Container information is carried and used as the key part of the HANDOVER COMMAND message to notify the UE through the source eNodeB.
When the source eNodeB receives the Handover Command message from the eCNS, the target eNodeB is ready for the handover. Therefore, the source eNodeB is required to transmit an RRC message to the UE and instructs the UE to hand over.
The source eNodeB is required to respond. For example, the SAE bearer is released based on the SAE bearer release list in the message.
