this patch refactors the SDU queuing and dropping policy of the RLC and PDCP layer.
the previous design had issues when packets have been generated at a higher
rate above the PDCP than they could be consumed below the RLC.
When the RLC SDU queues were full, we allowed two policies, one to block on the write
and the other to drop the SDU. Both options are not ideal because they either
lead to a blocking stack thread or to lost PDCP PDUs.
To avoid this, this patch makes the following changes:
* PDCP monitors RLC's SDU queue and drops packets on its north-bound SAP if queues are full
* a new method sdu_queue_is_full() has been added to the RLC interface for PDCP
* remove blocking write from pdcp and rlc write_sdu() interface
* all writes into queues need to be non-blocking
* if Tx queues are overflowing, SDUs are dropped above PDCP, not RLC
* log warning if RLC still needs to drop SDUs
* this case should be avoided with the monitoring mechanism
previously PDCP security (integrity and ciphering) could only
be enabled for both Rx and Tx at the same time.
this, however, caused an issue during the conformance testing in which,
in TC_8_2_1_1() for example, the eNB sends a SecModeCommand and a
RRC Reconfiguration in the same MAC TB. In this case, the eNB
needs to be able to enable DL security right after sending the SecModeCmd
in order to send the RRCReconfig encrypted. However, enabling UL security needs
to be postponed until after the SecModeComplete is received.
This patch allows to enable PDCP security for rx/tx independently if
that is needed. The default way is like before, enabling it for tx/rx at
the same time.
David Rupprecht
Codebot
Pedro Alvarez
faluco
Francisco
Andre Puschmann
Francisco Paisana
Xavier Arteaga