| CPC H04L 5/0044 (2013.01) | 12 Claims |

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1. A method for data transmission, comprising:
determining, by a terminal device, to change a radio link control (RLC) entity for transmitting a packet data convergence protocol (PDCP) protocol data unit (PDU), wherein RLC entities associated with a radio bearer comprise at least three RLC entities; and
determining, by the terminal device, a target RLC entity for transmitting the PDCP PDU and/or a target carrier used by a logical channel of the target RLC entity, comprising:
determining a primary RLC entity or a secondary RLC entity as the target RLC entity, in response to a sum of a data volume of a PDCP layer and a total data volume of an RLC layer associated with the radio bearer being larger than or equal to a preset threshold;
wherein the target RLC entity is determined from a primary RLC entity or a secondary RLC entity, the primary RLC entity and the secondary RLC entity are indicated in configuration signaling A received from a network device, wherein the configuration signaling A contains an indication field indicative of which of the at least three RLC entities being the primary RLC entity and which of the at least three RLC entities being the secondary RLC entity, and the primary RLC entity and the secondary RLC entity are used for transmitting non-duplicated data.
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