Sunday, 6 September 2015

LTE- S1interface


S1 Interface

The S1 interface connects the eNodeB and the mobility management entity (MME) or serving gateway (S-GW) and is classified into two planes: user plane and control plane.
The S1 interface transmits information about the following items based on the S1 Application Part (S1AP) protocol:

  • E-UTRAN management

  • Paging processing

  •  Mobility management

The S1 interface carries and transmits the service flows based on the GPRS Tunneling Protocol-User (GTPU) protocol. GPRS is short for general packet radio service.

Handover on the S1 Interface

  1.   The UE sends measurement reports to the eNodeB to instruct the eNodeB to initiate a handover.
  2. The source eNodeB sends a HandoverRequired message to the EPC
  3.  Upon receiving the HandoverRequired message, the EPC sends a HandoverRequest message to the target eNodeB
  4. Upon receiving the HandoverRequest message, the target eNodeB makes an admission decision and sends a HandoverRequestAck message to the EPC, acknowledging the handover
  5. Upon receiving the HandoverRequestAck message, the EPC sends a HandoverCommand message to request the source eNodeB to starts a handover 
  6. Upon receiving the HandoverCommand message, the source eNodeB sends the message to the UE
  7. The UE enters the target cell based on the information in the command. After successfully entering the target cell, the UE sends an RRCConnectionReconfigurationComplete message to the target eNodeB 
  8. Upon receiving the RRCConnectionReconfigurationComplete message, the target eNodeB sends a HandoverNotify message to the EPC 
  9.   Upon receiving the HandoverNotify message, the EPC sends a UEConextReleseCommand (cause = Successful Handover) message to the source eNodeB, indicating that the handover is successful and the UE can be released on the source eNodeB. After receiving the UEConextReleseCommand message, the source eNodeB waits until local data transmission is complete and then releases the UE.  

Budi Prasetyo

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