Here source eNB will send “RRC Connection Reconfiguration” to UE. This is because, the source eNB can forward packets received from SGW to target eNB.īelow image gives high level idea of steps performed during HO preparation. Now source eNB will create a bearer towards target eNB. It will send all the ID’s created in previous step. These 2 details will be shared to source eNB and then source eNB will share to UE. Target eNB will create “DRB ID”, “C-RNTI: Identifier for UE in a cell”, “X2 Target eNB TEID”. But till now downlink is not established. Now only UL has been established from Target eNB to SGW. It will have target eNB cellID, details of ERAB (QCI, ARP, S1 SGW TEID (UL)) to be established.Īs source eNB is sharing “S1 SGWTEID”, target eNB will make a uplink bearer to SGW with the help of “S1 SGWTEID”.

Source eNB will send a “HandoverRequest” message to TargeteNB. It will include “rsrpResult” and “rsrqResult”. Now, UE will move towards Target eNB, then UE will send measurement report to source eNB. Based on these configuration, UE will make the decision. It will have measObjectId, reportConfigId (A1, A2…). Signaling (dotted line) is shared between UE eNB MME and data (solid line) is shared between UE eNB SGW.ĭuring initial attach request, eNB will send “RRCConnectionReconfiguration” request.

SGW is connected to PGW.īoth source eNB and target eNB are connected to each other with help of X2 interface. We have 2 eNB, source eNB and Target eNB.

As we discussed in previous chapter, handover is based on 3 steps as below:

Step enb