Handover handling
A system is proposed to provide handover in a mobile telecommunications environment, particularly applicable to 3GPP networks, which does not increase signalling overhead but minimises user data loss during handover. In the modified system, PDCP SDUs with Sequence numbers are buffered and retransmitted as necessary. At the time of handover, SDUs not received by the user device are forwarded to the target base station for forward transmission to the UE. The handover procedure is designed to minimise packet loss whilst keeping to a minimum the duplication of packet transmission over the air interface.
1. A method performed by a source node which communicates with a target node, the method comprising:
receiving uplink Packet Data Convergence Protocol (PDCP) Service Data Units (SDUs);
transmitting, to the target node, a handover request;
receiving, from the target node, a handover response;
providing, to the target node, a status message, wherein the status message is configurable to include information for identifying at least a PDCP Sequence Number (SN) of a first missing uplink PDCP SDU; and
forwarding, to the target node, out-of-sequence uplink PDCP SDUs after sending the status message, wherein each forwarded uplink PDCP SDU is a data unit formed by processing at least one PDCP Protocol Data Unit (PDU) received at a PDCP entity.
2. The method according to claim 1 , wherein the method further comprises forwarding, to a gateway, uplink PDCP SDUs successfully received in-sequence upon handover.
3. The method according to claim 1 , wherein the out-of-sequence uplink PDCP SDUs are forwarded in case RLC Acknowledge Mode (AM) is applied.
4. The method according to claim 1 , wherein the handover response is transmitted, by the target node, in response to the handover request.
5. The method according to claim 1 , wherein the method further comprises transmitting, to a mobile station, a handover command after receiving the handover response.
6. The method according to claim 1 , wherein each PDCP SDU of the uplink PDCP SDUs comprises at least one RLC PDU.
7. The method according to claim 1 , wherein the source node is a source base station and the target node is a target base station.
8. The method according to claim 1 , wherein the status message is configurable to include further information for identifying out-of-sequence PDCP SDUs that need to be transmitted in a target cell.
9. A source node which communicates with a target node, the source node comprising:
a transceiver configured to:
receive uplink Packet Data Convergence Protocol (PDCP) Service Data Units (SDUs);
transmit, to the target node, a handover request;
receive, from the target node, a handover response;
provide, to the target node, a status message, wherein the status message is configurable to include information for identifying at least a PDCP Sequence Number (SN) of a first missing uplink PDCP SDU; and
forward, to the target node, out-of-sequence uplink PDCP SDUs after sending the status message, wherein each forwarded uplink PDCP SDU is a data unit formed by processing at least one PDCP Protocol Data Unit (PDU) received at a PDCP entity.
10. The source node according to claim 9 , wherein the transceiver is further configured to forward, to a gateway, uplink PDCP SDUs successfully received in-sequence upon handover.
11. The source node according to claim 9 , wherein the out-of-sequence uplink PDCP SDUs are forwarded in case RLC Acknowledge Mode (AM) is applied.
12. The source node according to claim 9 , wherein the handover response is transmitted, by the target node, in response to the handover request.
13. The source node according to claim 9 , wherein the transceiver is further configured to transmit, to a mobile station, a handover command after receiving the handover response.
14. The source node according to claim 9 , wherein each PDCP SDU of the uplink PDCP SDUs comprises at least one RLC PDU.
15. The source node according to claim 9 , wherein the source node is a source base station and the target node is a target base station.
16. The source node according to claim 9 , wherein the status message is configurable to include further information for identifying out-of-sequence PDCP SDUs that need to be transmitted in a target cell.