Scenario: A DL TBF is assigned over PCH (CCCH) and we start transmitting
DL data blocks blindly after X2002, but at the same time the MS start
packet-access-procedure to request an UL TBF.
Right now osmo-pcu correctly detects the MS is available in PDCH and
re-assigns a DL TBF using PACCH, but the LLC frames it transmitted in
the old PCH-assigned DL TBF get lost when that older TBF is freed
(because the DL blocks were removed from the GprsMs llc_queue).
This issue is now more frequent since X2002 timer was added recently to
delay starting requesting USF for a UL TBF, hence the contention
resolution in general takes more time and hence the PACCH assignment of
the DL TBF takes more time too, so more DL data blocks are transmitted
to the DL TBF assigned over PCH during that time.
This patch improves the situation to at least recover the DL blocks
transmitted if the DL TBF is freed (due to MS merge trigger by scenario
mentioned above), where no DL ACK/NACK was ever received by the MS.
Ideal solution would be to have complete tracking of which LLC PDUs from
the llc_queues were completely ACKed at RLC/MAC level, but that really
requires a lot of work and major refactoring, which are left as a future
improvement.
Change-Id: I9be4035fb2cf2b3ee56e91dcc12cc8c24028b4aa
Pau Espin
37c2f84d53