Question: Upon expiration of the `t-Reordering` timer in a 5G NR PDCP (Packet Data Convergence Protocol) entity, what action(s) are taken with stored PDCP SDUs (Service Data Units) having COUNT values less than RX_REORD?
Option 1: Deliver to upper layers after header decompression, and update RX_DELIV to the COUNT value of the first undelivered PDCP SDU with a COUNT value >= RX_REORD.
Option 2: Discard all stored PDCP SDUs with associated COUNT values < RX_REORD, and reset RX_REORD to RX_NEXT if RX_DELIV < RX_NEXT.
Option 3: Only deliver PDCP SDUs with consecutively associated COUNT values starting from RX_REORD, without updating RX_DELIV until all are delivered.
Option 4: Suspend delivery of new PDCP SDUs until the next `t-Reordering` timer expiration, to prioritize reordering.
Explanation: Upon `t-Reordering` expiration, the receiving PDCP entity delivers stored PDCP SDUs with COUNT values < RX_REORD (in ascending order, after decompression if needed) and updates RX_DELIV to the first undelivered PDCP SDU's COUNT value (>= RX_REORD), ensuring in-sequence delivery to upper layers while managing reordering boundaries. This aligns with efficient packet handling and reordering principles in wireless communications, particularly in 5G NR networks where maintaining sequence is crucial for data integrity.