Cedric Roux
d262d152ec
The necessity of SOstart/SOend was understood after email exchanges with David Breaux <davidbreaux67@gmail.com>. See openair2/LAYER2/rlc_v2/tests/test46.h for some details. Basically if we NACK without SOstart/SOend then the other end of the RLC channel will consider all the bytes as NACKed and will have to resend them all. If another status is then reported before all the bytes are sent, and because we don't use SOstart/SOend this status will NACK all the bytes again, then all the bytes are to be sent again. And the cycle repeats. It will end with a max retx reached (which triggers RLF, Radio Link Failure). The function put_bit in openair2/LAYER2/rlc_v2/rlc_pdu.c has been changed too, maybe introducing some performance issues.
50 lines
1.5 KiB
C
50 lines
1.5 KiB
C
/*
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* rlc am test ack/nack reporting with segmented SDUs
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* eNB sends SDU in big PDU, not received
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* eNB retx with smaller PDUs, not received except a few
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* after some time, RX works again, UE should NACK with SOstart/SOend
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*
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* this test was written because in the past we didn't generate NACKs with
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* SOstart/SOend, potentially leading to infinite retransmissions, even with
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* good radio conditions (well, there will be max ReTX reached at some point).
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* The scenario is as follows:
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* the eNB transmits many many PDUs segments and asks for status
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* report at some point (but before sending all the segments). The UE then
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* generates a (wrong) NACK without SOstart/SOend, and then the eNB has to
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* resend everything from start (all bytes of the PDU have been NACKed because
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* there is no SOstart/SOend). Then the eNB will again ask for status report
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* before sending everything and the process repeats all over again.
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*/
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TIME, 1,
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ENB_AM, 100000, 100000, 35, 0, 45, -1, -1, 4,
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UE_AM, 100000, 100000, 35, 0, 45, -1, -1, 4,
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UE_RECV_FAILS, 1,
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ENB_RECV_FAILS, 1,
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ENB_SDU, 0, 300,
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ENB_PDU_SIZE, 500,
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UE_PDU_SIZE, 1000,
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TIME, 2,
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ENB_PDU_SIZE, 7,
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TIME, 50,
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UE_RECV_FAILS, 0,
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TIME, 51,
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UE_RECV_FAILS, 1,
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TIME, 60,
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UE_RECV_FAILS, 0,
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TIME, 61,
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UE_RECV_FAILS, 1,
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TIME, 70,
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UE_RECV_FAILS, 0,
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TIME, 71,
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UE_RECV_FAILS, 1,
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TIME, 80,
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UE_RECV_FAILS, 0,
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TIME, 81,
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UE_RECV_FAILS, 1,
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TIME, 140,
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UE_RECV_FAILS, 0,
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ENB_RECV_FAILS, 0,
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TIME, 150,
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ENB_PDU_SIZE, 200,
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TIME, -1
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