LTE X2 handover source eNodeB flow PDF - EventHelix.com

Source eNodeB Interfaces (Successful Handover)LTE Mobile eNodeB Network Core NetworkUE Target eNodeB SourceeNodeBSGWEventStudio System Designer 620-Apr-13 22:03 (Page 1)This sequence diagram was generated with EventStudio Sytem Designer - http://www.EventHelix.com/EventStudio/eNodeBs in LTE are interconnected with the X2 interface. If two eNodeBs are served by the same MME, handover from thesource to the target eNodeB will take place over the X2 interface.Before the handoverRRC-ConnectedThe UE and Source eNodeB are in RRC Connected state.Downlink data flow before handoverDownlink data is flowing from the SGW to the UE via theSource eNodeB.Downlink Datas1_teid_dl1Downlink Datas1_teid_dl1Uplink data flow before handoverUplink data is flowing from the UE to the SGW via theSource eNodeB.Uplink Datas1_teid_ul1Uplink Datas1_teid_ul1Handover preparationrrcRRC Measurement ControlrrcThe network sets the measurement thresholds for sendingmeasurement reports.rrcRRC Measurement ReportrrcNeighboring cell signal quality is now better than the servingcell.Signal strength of serving cell,Signal strength of neighborsRRC: Handover needs to beperformed. A cell is selected forhandover.The RRC uses the latest measurement to decide if a handoveris needed to another cell. The target cell is selected. TheeNodeB for the target cell is identified.Derive KeNB*X2AP Handover Requestx2apx2apECGI of the Target Cell(of Target eNB),UE-AMBR,UE Security Capability,KeNB*,E-RAB to be setup(E-RAB ID, QCI, ARP, S1S-GW TEIDThe Source eNodeB initiates the handover with the HandoverRequest message. Information about active E-RABs, securitykeys is included in the message. (Click on the message nameabove the arrow to see message details)

Source eNodeB Interfaces (Successful Handover)LTE Mobile eNodeB Network Core NetworkUE Target eNodeB SourceeNodeBSGWX2AP Handover Request Acknowledgex2apx2apE-RAB ID,Target X2 eNB TEID,Transparent container =Handover CommandEventStudio System Designer 620-Apr-13 22:03 (Page 2)The Target eNodeB responds back to the source eNodeB witha Handover Request Acknowledge message. This messagecarries the Handover Command message (RRC ConnectionReconfiguration Request) in a transparent container. (Click onthe message name above the arrow to see message details)X2 Bearer Esablishmentx2_teidx2_teidAn X2 GTP connection is established between the Source andthe Target eNodeBs. This channel will carry the user dataduring the handover.Handover executionRRC Connection Reconfiguration RequestrrcRACH Preamble Assignment,Target C-RNTI,Target DRB ID (UL/DL),Target eNB AS Security AlgorithmrrcX2AP SN Transfer Statusx2apx2apDownlink PDCPSequence Number,Uplink PDCP SequenceNumberThe Source eNodeB sends a handover command to the UE.The message contains a new C-RNTI and new DRB IDs. ARACH preamble is also included for contention free RACHaccess.The PDCP sequence numbers are sent from the source to thetarget eNodeB. (Click on the message name above the arrow tosee message details)Downlink data flow during handover preparationAt this point all downlink data is getting reroutedfrom the source eNodeB to the target eNode.The data is being buffered at the target as the UEis yet to connect to the target.x2_teidDownlink Datas1_teid_dl1x2_teidDownlink Datas1_teid_dl1Uplink data flow during handover preparationThe uplink data is still being sent from the UE to the SGWvia the Source eNodeB.Uplink Datas1_teid_ul1Uplink Datas1_teid_ul1The UE is now connected to thetarget eNodeB. All the queuedmessages are now transmittedtowards the UE.RRC-IdleAt this point, the UE has detached from the source eNodeB butis still not communicating with the target eNodeB. The UE is inthe RRC-Idle state.Downlink data flow during handover executionDuring handover execution the data being routed from theSGW to the UE via the source and the target eNodeBs.