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A method of transmitting PDCP (Packet Data Convergence Protocol) status reports, is performed by a mobile terminal by receiving, from an upper layer, a request for PDCP (Packet Data Convergence Protocol) re-establishment; detecting whether there are any out-of-sequence PDCP SDUs (service data units)

A method of transmitting PDCP (Packet Data Convergence Protocol) status reports, is performed by a mobile terminal by receiving, from an upper layer, a request for PDCP (Packet Data Convergence Protocol) re-establishment; detecting whether there are any out-of-sequence PDCP SDUs (service data units) stored; and if there is at least one out-of-sequence PDCP SDU stored, allocating a bitmap field of length in bits equal to the number of PDCP SNs from and not including the first out-of-sequence PDCP SDU up to and including a last out-of-sequence PDCP SDU.

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1. A method comprising: processing, by a PDCP (Packet Data Convergence Protocol) entity located between upper layers and lower layers of a radio interface protocol stack, PDCP data units received from the lower layers after a PDCP re-establishment is requested from the upper layers;compiling, by the

1. A method comprising: processing, by a PDCP (Packet Data Convergence Protocol) entity located between upper layers and lower layers of a radio interface protocol stack, PDCP data units received from the lower layers after a PDCP re-establishment is requested from the upper layers;compiling, by the PDCP entity, a PDCP status report by,setting an FMS (First Missing Sequence number) field to a PDCP sequence number (SN) of a first missing PDCP SDU (Service Data Unit),if there is at least one out-of-sequence PDCP SDU stored, allocating a bitmap field of length in bits equal to the number of PDCP SNs from and not including the first missing PDCP SDU up to and including a last out-of-sequence PDCP SDUs, rounded up to the next multiple of 8,indicating a ‘0’ in corresponding positions of the bitmap field for all PDCP SDUs that have not been received as indicated by the lower layers, andindicating a ‘1’ in corresponding positions of the bitmap field for all other PDCP SDUs; andsending, from the PDCP entity to the lower layers, the PDCP status report as a PDCP PDU (Protocol Data Unit) for transmission to a peer PDCP entity at a receiving side. 2. The method of claim 1, wherein the compiling step is performed if a radio bearer is configured by the upper layers to send the PDCP status report via uplink transmission. 3. The method of claim 1, wherein the step of indicating a ‘0’ in corresponding positions of the bitmap field is optionally also performed for PDCP SDUs for which decompression has failed. 4. The method of claim 1, wherein the steps are performed for an RLC (Radio Link Control) AM (Acknowledged Mode). 5. The method of claim 1, wherein the PDCP re-establishment occurs for handover (HO) situations. 6. The method of claim 1, wherein the PDCP status report as the PDCP PDU is a PDCP Control PDU with a format including a D/C (Data/Control) field of 1 bit, followed by a PDU Type field of 3 bits, followed by the FMS field of 12 bits, and optionally followed by the bitmap field of 8 bits or a multiple thereof. 7. A method comprising: receiving, by a PDCP (Packet Data Convergence Protocol) entity located between upper layers and lower layers of a radio interface protocol stack, a PDCP status report as a PDCP PDU (Protocol Data Unit) transmitted from a peer PDCP entity at a transmitting side,said PDCP status report generated in the peer PDCP entity at the transmitting side by,processing PDCP data units received from the lower layers at the transmitting side after a PDCP re-establishment is requested from the upper layers at the transmitting side,compiling the PDCP status report bysetting an FMS (First Missing Sequence number) field to a PDCP sequence number (SN) of a first missing PDCP SDU (Service Data Unit),if there is at least one out-of-sequence PDCP SDU stored, allocating a bitmap field of length in bits equal to the number of PDCP SNs from and not including the first missing PDCP SDU up to and including a last out-of-sequence PDCP SDUs, rounded up to the next multiple of 8,indicating a ‘0’ in corresponding positions of the bitmap field for all PDCP SDUs that have not been received as indicated by the lower layers at the transmitting side, andindicating a ‘1’ in corresponding positions of the bitmap field for all other PDCP SDUs; andsending the PDCP status report from the peer PDCP entity at the transmitting side; andprocessing the PDCP status report received from the peer PDCP entity at the transmitting side. 8. The method of claim 7, wherein the compiling step is performed by the peer PDCP entity at a transmitting side if a radio bearer is configured by the upper layers to send the PDCP status report via uplink transmission. 9. The method of claim 7, wherein the step of indicating a ‘0’ in corresponding positions of the bitmap field is optionally also performed by the peer PDCP entity at a transmitting side for PDCP SDUs for which decompression has failed. 10. The method of claim 7, wherein the steps are performed for an RLC (Radio Link Control) AM (Acknowledged Mode). 11. The method of claim 7, wherein the PDCP re-establishment occurs for handover (HO) situations. 12. The method of claim 7, wherein the PDCP status report as the PDCP PDU is a PDCP Control PDU with a format including a D/C (Data/Control) field of 1 bit, followed by a PDU Type field of 3 bits, followed by the FMS field of 12 bits, and optionally followed by the bitmap field of 8 bits or a multiple thereof. 13. An apparatus comprising: a PDCP (Packet Data Convergence Protocol) entity at a transmitting side;upper layers located above the PDCP entity in a radio interface protocol stack; andlower layers located below the PDCP entity in the radio interface protocol stack,wherein the PDCP entity at the transmitting side is configured to perform,processing PDCP data units received from the lower layers after a PDCP re-establishment is requested from the upper layers;compiling a PDCP status report by,setting an FMS (First Missing Sequence number) field to a PDCP sequence number (SN) of a first missing PDCP SDU (Service Data Unit),if there is at least one out-of-sequence PDCP SDU stored, allocating a bitmap field of length in bits equal to the number of PDCP SNs from and not including the first missing PDCP SDU up to and including a last out-of-sequence PDCP SDUs, rounded up to the next multiple of 8,indicating a ‘0’ in corresponding positions of the bitmap field for all PDCP SDUs that have not been received as indicated by the lower layers, andindicating a ‘1’ in corresponding positions of the bitmap field for all other PDCP SDUs; andsending, to the lower layers, the PDCP status report as a PDCP PDU (Protocol Data Unit) for transmission to a peer PDCP entity at a receiving side. 14. An apparatus comprising: a PDCP (Packet Data Convergence Protocol) entity at a receiving side;upper layers located above the PDCP entity in a radio interface protocol stack; andlower layers located below the PDCP entity in the radio interface protocol stack,wherein the PDCP entity at the receiving side is configured to perform,receiving a PDCP status report as a PDCP PDU (Protocol Data Unit) transmitted from a peer PDCP entity at a transmitting side,said PDCP status report generated in the peer PDCP entity at the transmitting side by,processing PDCP data units received from the lower layers at the transmitting side after a PDCP re-establishment is requested from the upper layers at the transmitting side,compiling the PDCP status report bysetting an FMS (First Missing Sequence number) field to a PDCP sequence number (SN) of a first missing PDCP SDU (Service Data Unit),if there is at least one out-of-sequence PDCP SDU stored, allocating a bitmap field of length in bits equal to the number of PDCP SNs from and not including the first missing PDCP SDU up to and including a last out-of-sequence PDCP SDUs, rounded up to the next multiple of 8,indicating a ‘0’ in corresponding positions of the bitmap field for all PDCP SDUs that have not been received as indicated by the lower layers at the transmitting side, andindicating a ‘1’ in corresponding positions of the bitmap field for all other PDCP SDUs; andsending the PDCP status report from the peer PDCP entity at the transmitting side; andprocessing the PDCP status report received from the peer PDCP entity at the transmitting side.