From 26d68e9c5e624c3719f9d86f1ba8a9f5739c832f Mon Sep 17 00:00:00 2001
From: Cedric Roux <cedric.roux@eurecom.fr>
Date: Fri, 2 Mar 2018 12:02:06 +0100
Subject: [PATCH] hotfix: fix bad RLC UM packet creation
Running TCP DL traffic with one connected UE showed a lot of
fluctuations in throughput. After analysis it was found that
sometimes the RLC UM PDU was not correct. It contained one byte
more than it should. On the receiver side, the TCP packet
contained in the RLC packet seems to be rejected by the TCP
stack of the UE (it has one byte more than it should),
leading to a brutal reduction of the throughput, probably due
to some congestion detection in the TCP implementation.
Or something.
This hotfix seems to solve the problem. Using iperf in downlink
with a 5MHz eNB, we see no more fluctuations, the traffic is
very steady at 16.8Mb/s, as reported by the iperf server running
on the phone. (17.5 in the PHY plot of the T tracer.)
A rewrite of both the MAC and RLC UM packet generation is needed.
The code is way too complex for what it does and may contain
several similar problems that only trigger in specific rare
conditions.
---
openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_segment.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_segment.c b/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_segment.c
index f9af7c1cc2..98a44ceeeb 100644
--- a/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_segment.c
+++ b/openair2/LAYER2/RLC/UM_v9.3.0/rlc_um_segment.c
@@ -172,7 +172,7 @@ rlc_um_segment_10 (const protocol_ctxt_t* const ctxt_pP, rlc_um_entity_t *rlc_pP
test_pdu_remaining_size = 0;
test_remaining_size_to_substract = 0;
test_remaining_num_li_to_substract = 0;
- pdu_remaining_size = pdu_remaining_size - (test_li_length_in_bytes ^ 3);
+ //pdu_remaining_size = pdu_remaining_size - (test_li_length_in_bytes ^ 3);
} else if ((sdu_mngt_p->sdu_remaining_size + (test_li_length_in_bytes ^ 3)) < test_pdu_remaining_size ) {
test_num_li += 1;
num_fill_sdu += 1;
@@ -365,9 +365,9 @@ rlc_um_segment_10 (const protocol_ctxt_t* const ctxt_pP, rlc_um_entity_t *rlc_pP
sdu_mngt_p->sdu_remaining_size,
pdu_remaining_size - sdu_mngt_p->sdu_remaining_size);
#endif
-#if !EXMIMO
- assert(1!=1);
-#endif
+//#if !EXMIMO
+// assert(1!=1);
+//#endif
memcpy(data, data_sdu_p, sdu_mngt_p->sdu_remaining_size);
// reduce the size of the PDU
continue_fill_pdu_with_sdu = 0;
--
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