LTE: What does mean by Timer based discard and how it works ?

Question

In PDCP layer, there is functionality of timer based discard. Can anyone please elaborate on this functionality of PDCP layer.

Answer 1

Every bearer has it's own QoS requirements like delay budget etc. Due to such requirement, when PDCP layer receives a PDCP SDU it starts a timer of each received packet since If this received PDCP SDU can't be transmitted in reasonable time frame, it will be too late for receiver application to accept this packet. in such scenario re-transmission will occur at application level.

Answer 2

The transmitting side of each PDCP entity for DRBs shall maintain the timers.
DiscardTimer:
The duration of the timer is configured by upper layers . In the transmitter, a new timer is started upon reception of an SDU from upper layer.