Bug during a handover in a simple asymmetric Dual Connectivity scenario

Hello,

I have encountered a bug in the NSA handover procedure, and during my research, I think I came across a similar open issue: https://github.com/Unipisa/Simu5G/issues/112.

The issue arises in a simple scenario where an UE moves eastward and sends UL packets to the server node without any interference. Initially, the UE is connected to eNB1/gNB1 through NSA coupling and later switches to eNB2 during the handover approximately at the 29th second. However, after the handover, the UE stops sending any packets to the server. The message dialogue shows that the UE sends airframes to eNB2, but there is no further progress. This issue persists regardless of the value of the tos parameter (three different configurations in ini file for LTE, NR and SB were tested).

I would appreciate your insights into the possible cause of this bug. I have limited knowledge about the inner workings and the whole idea of the handover procedure and dual connectivity management. Could you shed some light on the source of this issue and provide guidance on how to address it?

Thank you and best regards,
Nikita

P.S. I have attached the scenario in the archive, and the network topology is illustrated in the picture below. The scenario is expected to be extracted in simu5G/simulations/NR folder

dc_bug.zip

Start by extracting dc_bug.zip into simu5G/simulations/NR and run the simple asymmetric Dual Connectivity scenario described; inspect the handover around 29 seconds and its message dialogue. Done means the UE resumes sending UL packets to the server after switching from eNB1/gNB1 to eNB2, with behavior checked across the stated tos configurations.