What is DL and UL PDCP aggregation in NR?
To use PRBs from both RATs simultaneously.
The basic principle of split bearer in DC is that one PDCP with two RLC entities. One RLC entity for each of LTE & NR and the RLC SDUs from both of these RLC entities will aggregate at PDCP layer. This is called PDCP aggregation. In case of SN terminated split bearer in ENDC, PDCP aggregation happens at gNB and in case of MN terminated split bearer, PDCP aggregation happens at LTE.