[srsran-users] [ZMQ][TB Decode]

[Nikolaos Apostolakis]

Hello all,

I am using srsENB that interacts with srsUE through the zMQ driver. I am 
trying to emulate a scenario that due to bad conditions srsENB can't 
decode the TB of the PUSCH, which are sent by the UE. Theoretically, eNB 
should send NACK messages 3ms after the UL grant has been sent provoking 
retransmissions from the UE side and consequently yielding 0 throughput.

To simulate this, I implement a 10ms delay within the 
/srsRAN/lib/src/phy/phch/sch.c#srsran_ulsch_decode.

srsENB is connected to the srsEPC where an iperf server is running 
(everything running within Docker containers on the same host). On UE, I 
execute iperf tests towards this iperf server. I have appropriately set 
the routing table of the NS of the UE, so that it sends the traffic 
towards the tun_srsue interface.

While expecting near to 0 throughput, I still keep receiving close to 
4.5Mbps throughput after several executions. Even with higher > 10ms 
delay, I still observe considerable throughput.

What I would like to ask if it's my theoretical consideration of the 
NACK mechanisms is false or there is a technical detail that I am missing.
Is the zMQ driver skipping some of the High-PHY procedures? (reading 
through the code, I have seen it doesn't).

Thanks a lot,

Nikos Apostolakis
PhD Student
IMDEA Networks Institute