Below shows a schematic diagram of PDCP duplication:
If PDCP duplication is not enabled, a PDCP packet will be transmitted to an RLC entity and RLC entity will send to MAC layer.
If PDCP duplication is enabled, PDCP packet will be transmitted to 2 RLC entities, i.e Primary RLC entity and Secondary RLC entity.
They both will process independently and transmit the processed packet to MAC layer.
From MAC perspective , they both are different independent packets.
This is done to enhance reliability and reduce time delay.
PDCP duplication Procedure
Activation/Deactivation of PDCP duplication
If a PDCP entity is configured with pdcp-Duplication, the transmitting PDCP entity shall:
-> Activate PDCP duplication for SRB and DRB.
If the deactivation of PDCP duplication is indicated then: Deactivate the PDCP duplication.
Duplicate PDU discard
If a PDCP entity is configured with pdcp-Duplication, the transmitting PDCP entity shall:
If there is a successful delivery of the PDCP data PDU is confirmed by one of two associated AM RLC entities then:
– indicate to the other AM RLC entity to discard the duplicated PDCP Data PDU;
– if the deactivation of PDCP duplication is indicated:
– indicate to the secondary RLC entity to discard all duplicated PDCP Data PDUs.
Source TS 38 323