A data processing method, performed by a data sending apparatus, comprising: receiving, at a Radio Link Control, RLC, layer, a data packet from a Packet Data Convergence Protocol, PDCP, layer, wherein the data packet is used as an RLC service data unit, SDU; and encapsulating, at the RLC layer, the RLC SDU into at least one RLC protocol data unit, PDU, wherein each of the at least one RLC PDU encapsulated at the RLC layer comprises a header and a payload, the header comprises a segment indicator, SI, field with two bits, a first value of the two bits indicates that what is encapsulated into an RLC PDU where the SI field is located is a complete RLC SDU, a second value of the two bits indicates that what is encapsulated into an RLC PDU where the SI field is located is a first segment of an RLC SDU, a third value of the two bits indicates that what is encapsulated into an RLC PDU where the SI field is located is a middle segment of an RLC SDU, and a fourth value of the two bits indicates that what is encapsulated into an RLC PDU where the SI field is located is a last segment of an RLC SDU, and the payload is used to carry data from a single RLC SDU, the RLC SDU is encapsulated into a plurality of RLC PDUs, the headers of the plurality of RLC PDUs comprise sequence number, SN, fields, and SNs in the SN fields are the same; and the plurality of RLC PDUs comprise a first RLC PDU with a first segment of the RLC SDU and a second RLC PDU with a last segment of the RLC SDU, wherein the header of the first RLC PDU comprises an SN field with the same SN and an SI field with the second value, and has no segment offset, SO, field, and the payload of the first RLC PDU comprises the first segment of the RLC SDU; the header of the second RLC PDU comprises an SN field with the same SN, an SI field with the fourth value, and an SO field indicating a byte offset, of a first byte of the payload of the second RLC PDU, within the RLC SDU, and the payload of the second RLC PDU comprises the last segment of the RLC SDU. receiving, at a Radio Link Control, RLC, layer, a data packet from a Packet Data Convergence Protocol, PDCP, layer, wherein the data packet is used as an RLC service data unit, SDU; and encapsulating, at the RLC layer, the RLC SDU into at least one RLC protocol data unit, PDU, wherein each of the at least one RLC PDU encapsulated at the RLC layer comprises a header and a payload, the header comprises a segment indicator, SI, field with two bits, a first value of the two bits indicates that what is encapsulated into an RLC PDU where the SI field is located is a complete RLC SDU, a second value of the two bits indicates that what is encapsulated into an RLC PDU where the SI field is located is a first segment of an RLC SDU, a third value of the two bits indicates that what is encapsulated into an RLC PDU where the SI field is located is a middle segment of an RLC SDU, and a fourth value of the two bits indicates that what is encapsulated into an RLC PDU where the SI field is located is a last segment of an RLC SDU, and the payload is used to carry data from a single RLC SDU, the RLC SDU is encapsulated into a plurality of RLC PDUs, the headers of the plurality of RLC PDUs comprise sequence number, SN, fields, and SNs in the SN fields are the same; and the plurality of RLC PDUs comprise a first RLC PDU with a first segment of the RLC SDU and a second RLC PDU with a last segment of the RLC SDU, wherein the header of the first RLC PDU comprises an SN field with the same SN and an SI field with the second value, and has no segment offset, SO, field, and the payload of the first RLC PDU comprises the first segment of the RLC SDU; the header of the second RLC PDU comprises an SN field with the same SN, an SI field with the fourth value, and an SO field indicating a byte offset, of a first byte of the payload of the second RLC PDU, within the RLC SDU, and the payload of the second RLC PDU comprises the last segment of the RLC SDU.