| CPC H04W 12/106 (2021.01) [H04L 1/1671 (2013.01); H04L 5/0055 (2013.01); H04L 47/32 (2013.01); H04L 69/22 (2013.01); H04W 12/0433 (2021.01); H04W 36/00698 (2023.05); H04W 76/30 (2018.02)] | 20 Claims |

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1. A method performed by a terminal in a wireless communication system, the method comprising:
receiving, from a base station, a radio resource control (RRC) message including information indicating a change from a first packet data convergence protocol (PDCP) entity for a bearer to a second PDCP entity for the bearer, the first PDCP entity and the second PDCP entity being in the terminal;
identifying whether the first PDCP entity for the bearer is changed to the second PDCP entity for the bearer based on the information indicating the change;
processing data with a PDCP sequence number for the first PDCP entity as new data for the second PDCP entity, in case that the first PDCP entity for the bearer is changed to the second PDCP entity for the bearer;
releasing the first PDCP entity;
configuring a new PDCP header associated with the data; and
encrypting the data with a new security key,
wherein the PDCP sequence number for the first PDCP entity is greater than or equal to the PDCP sequence number of data for which successful transmission is not acknowledged from a radio link control (RLC) entity.
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