DL Throughput Behave differnt with RLC SN=12 & 18

[IbrahimBabiker87]

Issue Description

when using RLC configuration in QCI=9 { AM::Acknowledged mode} specifically main parameter : SN length and set it to 12 instead of the default 18; the DL physical layer throughput hit 1.54 Gbps while app layer { iperf3} is about ~900 Mbps. { snapshots attached } The SN in PDCP was 18 in both cases, this should not affect the behavior of throughput , right ?

Setup Details

SRS release_24_04

Expected Behavior

to work fine

Actual Behaviour

DL throughput {app layer : iperf3} with RLC: SN = 12 & PDCP:SN=18 is less than with RLC: SN = 18 & PDCP:SN=18

Steps to reproduce the problem

set QCI= 9 QOS configuration so that the RLC mode = AM, and with RLC: SN = 12 & PDCP:SN=18

Additional Information

below is DL physical layer throughput with RLC: SN = 12 & PDCP:SN=18

below is the app layer { iperf3} Dl throughput:

[alvasMan]

Hi @IbrahimBabiker87,

Using 12 bits may cause the RLC TX window to get full, which may explain the low application throughput, but then the high throughput at the lower layers then seems strange.

I'll try to replicate this, but in the meantime could you send some logs with RLC at info? Also, could you enable the RLC metrics with metrics --rlc_report_period=1000? This give us an overview of the tput the RLC is sending to the lower layers.

[IbrahimBabiker87]

@alvasMan ,

Thank you for your response,

here you go attched the requested data, https://drive.google.com/file/d/1LNI2AVdg1xpvyVN7xGzkfjZ4NnreGblL/view?usp=sharing

below are the results when using SN=12 in RLC layer Throughput shown by SRS 1.4 Gbps

Throughput shown by iperf3 ~500 Mbps:

[IbrahimBabiker87]

@alvasMan

its worth to mention that the above test is DL only, However, when using bidirectional traffic the DL throughput hit 1.1 ~ 1.2 Gbps

SRS output:

Iperf3: " bidirectional"