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.
The problem is the following (as reported by an user):
"one UE is attached to OAI system. UE is near the antenna. Try to detach
the UE and attach again. Repeat this procedure for 5-6 times. OAI system
does not work and any the UE can not attach to this system. I use TEMS
software and I can see MIB signaling on this UE but UE can not decode SIB1
and SIB2."
What happens is that the DCI for SIB1 and SIB2 is not cleared before
use. That is the bits in the 'padding' field keep the values that were
set before. If the structure has been used to transmit other DCIs
(eg. for UEs) in the past, it may be reused with some of those bits set
to 1. When receiving this DCI, the UE won't accept it because it
gets some bits at 1 where it expects them to be 0.
The short-term/quick solution is to clear the 'padding' field.
A better solution would be to rewrite this part of the code,
which is way too complicated for what it does. But this takes
too much time.
In dci.h the field 'dummy' of some structures was renamed to 'padding'.
The fields 'padding32' and 'padding64' were also renamed to 'padding'
for consistency.
Some structures (DCI2B_1_5MHz_TDD, DCI2B_10MHz_FDD, DCI2D_1_5MHz_FDD,
DCI2D_5MHz_FDD, DCI2D_10MHz_FDD) had a 'padding' field at the end, which
was renamed to 'padding0'. I don't know if this field should be here at all.
To me this field looks very suspicious. When we test DCIs 2B and 2D we
should be careful.
(cherry picked from commit c5ca2bd862)
Summary of changes:
- fix dlsim/ulsim
- fix centOS compilation
- Move the accounting phase of the DL pre-processor in a separate procedure
and fix some issues
- additional Mac stats and Improvements
- minor fix in test setup v2
Wang Tsu-Han